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by diagrammo

@diagrammo/dgmo-mcp

Turn a conversation into a real diagram — without leaving your AI tool.

npm version npm downloads license

This MCP server gives Claude (and any MCP-compatible AI tool) the ability to render sequence diagrams, flowcharts, ER diagrams, C4 architecture, gantt charts, and 40+ other chart types from concise text markup — then hand the result off to a full editor for refinement. Ask for a diagram in chat; get a real one back.

What you can do

Ask in plain language — "diagram the auth flow as a sequence", "chart the Q3 plan as a gantt", "draw our services as a C4 diagram" — and Claude writes the markup and renders it. The markup stays readable and diffable:

flowchart Mutiny Resolution
direction-tb

[Sail]     Set sail under the captain
{Trouble?} Discontent in the crew?
{Vote}     Crew vote called
[Mutiny]   Seize the ship

(Sail) -> (Trouble?)
(Trouble?) -Yes-> (Vote)
(Vote) -Mutiny-> (Mutiny)

→ renders to the flowchart above. All rendering happens locally — no diagram data leaves your machine.

Related MCP server: drawio

Tools

Tool

What it does

Over HTTP

render_diagram

Render DGMO markup to SVG or PNG

yes

validate_diagram

Check markup and report parse errors, without rendering

yes

suggest_chart_type

Suggest the chart types that fit a description

yes

list_chart_types

List all supported chart types, marking the beta ones

yes

get_language_reference

Get DGMO syntax documentation for accurate generation

yes

get_examples

Fetch worked examples for a chart type

yes

share_diagram

Get a shareable diagrammo.app URL — hand your diagram to the web editor

yes

open_in_app

Open the diagram straight into the Diagrammo desktop app for editing

no

check_app_installed

Report whether the desktop app is installed

no

preview_diagram

Render one or more diagrams and open an HTML preview in the browser

no

generate_report

Build a polished multi-section HTML report with ToC and optional source

no

put_space_diagram

Write a diagram into a Diagrammo Cloud space, by folder and title

yes

get_space_diagram

Read a diagram from a Cloud space, by id or by folder and title

yes

list_space_diagrams

List every diagram in a Cloud space

yes

The three space tools send the diagram to Diagrammo Cloud. They need a space API key (minted on the Diagrammo account page) as DGMO_API_KEY in the server's environment — never as a tool argument, so the key stays out of the transcript.

share_diagram and open_in_app are the bridge out of chat: a diagram Claude generates becomes something you can refine, restyle, and embed — see below.

The four marked no open a browser or launch the desktop app. Over HTTP that would happen on the machine running the server rather than on yours, so they are not offered there — see Serving over HTTP.

Beyond the MCP server

The MCP server is one entry point into Diagrammo — a whole ecosystem built on the same DGMO markup. Generate in chat, refine in a real editor, embed anywhere:

  • diagrammo.app — the desktop app. open_in_app drops an AI-generated diagram straight into it, with live preview, palettes, and export.

  • online.diagrammo.app — a full editor in the browser, zero install. share_diagram URLs open right here.

  • Docs integrations — drop DGMO fenced code blocks into your docs site: remark-dgmo, astro-dgmo, docusaurus-plugin-dgmo, fumadocs-dgmo.

  • Obsidian — the Diagrammo Diagrams community plugin renders DGMO in your vault.

  • CLI — npx @diagrammo/dgmo-cli file.dgmo -o out.png, or install it with npm install -g @diagrammo/dgmo-cli (macOS and Linux).

One markup, everywhere. A diagram you generate here renders identically in the app, in your docs, and in Obsidian — because they all speak DGMO.

→ Try it free at diagrammo.app

Setup

Easiest — one command

Install the dgmo CLI and let it wire everything up:

npm install -g @diagrammo/dgmo-cli   # macOS and Linux
dgmo install                         # auto-detects Claude Code, Codex, Claude Desktop, Cursor, …

Prefer Homebrew or pacman? See diagrammo.app/dev.

dgmo install configures each detected assistant non-interactively and points it at dgmo mcp, so there's no separate package to install or prompts to answer. Target one surface with dgmo install claude-code (or codex, claude-desktop, …).

Manual configuration

Prefer to edit configs yourself? Point any MCP client at the server via npx (no global install needed):

Claude Code — .claude/settings.local.json; Claude Desktop — ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "dgmo": {
      "command": "npx",
      "args": ["-y", "@diagrammo/dgmo-mcp"]
    }
  }
}

If you have the dgmo CLI installed, { "command": "dgmo", "args": ["mcp"] } works too. Restart the client after saving — the tools appear automatically.

Serving over HTTP

The setups above launch the server as a child process and talk to it over its standard input and output. That needs the server and the client on the same machine. Where they are not — a hosted agent platform, a container, one server shared by several people — start it as an HTTP endpoint instead:

npx -y @diagrammo/dgmo-mcp --http            # http://127.0.0.1:3333/mcp
MCP_TRANSPORT=http MCP_PORT=8080 npx -y @diagrammo/dgmo-mcp

Every option takes a flag or an environment variable, whichever your setup can express:

Flag

Variable

Default

What

--http

MCP_TRANSPORT=http

off

Serve streamable HTTP instead of stdio

--port <n>

MCP_PORT

3333

Port to listen on

--host <addr>

MCP_HOST

127.0.0.1

Interface to bind

--path <path>

MCP_PATH

/mcp

Path the endpoint answers on

--allow-host <h>

MCP_ALLOWED_HOSTS

loopback

Extra Host headers to accept, repeatable

--allow-origin <o>

MCP_ALLOWED_ORIGINS

unset

Origin headers to accept, repeatable

Each request is served independently — no sessions, nothing kept between calls — so one endpoint can serve several clients at once.

The server has no authentication of its own. It binds loopback by default and rejects requests carrying a Host header it was not told to expect, which is enough for a client on the same machine or inside the same container. Anything reachable from a wider network needs your own authentication in front of it, and --allow-host for the hostname it will be reached by. Binding a non-loopback interface without naming a host prints a warning saying so.

--help prints all of this from the installed version.

Privacy

All rendering is local. Your diagram markup and the images it produces never leave your machine, except when you explicitly call share_diagram (which encodes the diagram into a diagrammo.app URL). See the privacy terms.

Dev hub (AI-tuning tools)

pnpm hub

One command, one server, one browser tab. The hub opens a tabbed shell over the three AI-tuning dev tools — switch between them with the top tabs, no separate ports or commands to remember:

  • Trigger tuning — edit the phrase/concept vocabulary that drives suggest_chart_type, score prompts live, save back to triggers.json.

  • LLM judge — judge chart-type descriptions against prompts with claude -p.

  • Guidance studio — author the per-type styling guidance the server delivers (the <!-- TIPS --> blocks in dgmo's language-reference.md, sliced into get_language_reference): pick a type, edit how the AI is told to style it, run a prompt against a committed dataset fixture (so inputs never move between runs), and see the generated DGMO + rendered image side by side. The picker doubles as a coverage bar; "Compare 3×" renders no-guidance vs your tips for a by-eye check; Save validates and writes back to language-reference.md.

These tools are dev-only and never bundled into the published server. (The standalone pnpm harness and pnpm studio scripts still run a single tool each if you ever want one in isolation.)

Contributing & releases

Development setup and the release workflow live in CONTRIBUTING.md.

License

MIT

Available Tools

11 tools
check_app_installedA
Read-only

Check whether the Diagrammo desktop app is installed. Returns a sentence naming the output route the product prefers, plus JSON { installed, paths, platform }. Detection is macOS-only; other platforms always report not installed. The answer does not change within a session, so one call is enough before deciding how to show a diagram: when installed, the preferred route is open_in_app with filePath; otherwise share_diagram.

ParametersJSON Schema
NameRequiredDescriptionDefault

No parameters

TDQS

A4.9/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnly/non-destructive annotations, it discloses three non-obvious traits: detection is macOS-only with other platforms always reporting not installed, the result is stable within a session so caching is safe, and the return is a prose sentence plus a JSON object with named keys.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with the core purpose, then output shape, then the platform caveat and decision rule. No filler and every clause carries actionable information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description compensates by naming the return shape (sentence plus { installed, paths, platform }), and it supplies the decision context the agent needs. Nothing required to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

This tool takes zero parameters, so there is nothing to document and the baseline is 4. The mention of `filePath` refers to open_in_app's parameter, not this tool's, so it neither helps nor hurts.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource ('Check whether the Diagrammo desktop app is installed') and immediately distinguishes itself from sibling tools like open_in_app and share_diagram by naming them as the consumers of its result.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives explicit when-to-use guidance ('one call is enough before deciding how to show a diagram') and a complete decision rule: installed → open_in_app with `filePath`, otherwise → share_diagram. When-not-to-use is implied by the session-stable note, which tells the agent not to call repeatedly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

generate_reportA

Generate a polished HTML report with multiple DGMO diagrams, table of contents, and optional source blocks. Opens in browser by default. For DGMO syntax call get_language_reference.

ParametersJSON Schema
NameRequiredDescriptionDefault
openNoOpen the report in the browser
themeNoColor themelight
titleYesReport title
paletteNoColor palette for the page and every diagram. Given, it beats each diagram's own palette line; omitted, each diagram uses its own, and the page uses slate.
sectionsYesReport sections, each with a diagram
subtitleNoOptional subtitle
include_sourceNoShow DGMO source in collapsible blocks

TDQS

A4.1/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false, openWorldHint=true, and destructiveHint=false, lowering the bar. The description adds a genuinely useful side-effect disclosure ('Opens in browser by default') that the annotations do not convey, though it omits where the report file is written or returned.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the core capability, then the behavioral default, then the prerequisite pointer. Zero filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description should carry the return-value burden, but it only says the report 'opens in browser by default'. For a tool that produces a file artifact, the missing output location/path leaves the agent unable to report where the report lives.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so each parameter is already documented, giving a baseline of 3. The description lightly reinforces 'source blocks' (include_source) and browser opening (open) but adds no syntax or precedence detail beyond the schema, which already explains palette behavior better.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Generate a polished HTML report') and enumerates the distinguishing output features (multiple DGMO diagrams, table of contents, optional source blocks). This clearly separates it from single-diagram siblings like render_diagram and preview_diagram.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides one explicit routing pointer ('For DGMO syntax call get_language_reference') that resolves the likely prerequisite. However, it does not state when to choose this over render_diagram or preview_diagram, so usage context is clear but incomplete.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

get_examplesA

Get example DGMO diagrams for a chart type. Returns real-world examples from the gallery that demonstrate syntax patterns. Use these as few-shot references when generating new diagrams.

ParametersJSON Schema
NameRequiredDescriptionDefault
chart_typeNoChart type to get examples for (e.g. "sequence", "infra", "bar"). Omit to list all available example names.

TDQS

A4.1/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden. It states it returns real-world examples, but does not mention behavior when the parameter is omitted (lists all names) or any read-only implications. Adequate but not fully transparent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short, front-loaded sentences with no redundancy. Every phrase earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a tool with one optional parameter and no output schema, the description fully explains purpose, return content, and usage context. Complete for its complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the description does not need to add much. It provides example values and tells to omit for listing names, which adds slight value beyond the schema. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('get'), the resource ('example DGMO diagrams for a chart type'), and the purpose ('few-shot references'). It is specific and distinguishes from siblings like generate_report or validate_diagram.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly says 'Use these as few-shot references when generating new diagrams,' indicating when to use. It does not explicitly state when not to use or mention alternatives, but the context makes it clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

get_language_referenceA
Read-onlyIdempotent

Get the DGMO language reference. With chart_type, returns that type's section plus the universal rules every diagram follows (the closed color set, titles, categorize-and-color). Without it, returns the entire reference for all chart types, which is very large (hundreds of KB); pass chart_type whenever the type is known. Errors when the type has no documented section — call list_chart_types for the valid ids. suggest_chart_type already appends the chosen type's section, so a call here is only needed after the user picks a type or when switching types.

ParametersJSON Schema
NameRequiredDescriptionDefault
chart_typeNoOptional chart type to get reference for (e.g. "sequence", "flowchart", "bar")

TDQS

A4.8/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/non-destructive, but the description adds genuinely new behavioral context: the no-argument call returns a very large payload (hundreds of KB), an error occurs for undocumented types, and the returned content includes universal rules (color set, titles, categorize-and-color). This is exactly the kind of cost/error/redundancy disclosure annotations cannot carry.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three dense sentences, front-loaded with the core action before the conditional behavior and the sibling-avoidance note. Every clause carries information; it is slightly long but no sentence is filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, so the description must describe return values, and it does: the type section plus universal rules, or the full reference. Error behavior, alternatives, and payload-size trade-offs are all covered, leaving nothing an agent needs to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3; the description goes beyond it by explaining the effect of the parameter (returns that type's section plus universal rules), the consequence of omitting it (entire reference, very large), and the failure mode (errors for undocumented types, ids via list_chart_types). Only the absence of example id syntax keeps it from a 5.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Get the DGMO language reference') and precisely scopes the two modes of operation (with vs. without chart_type). It explicitly distinguishes itself from siblings suggest_chart_type and list_chart_types, so an agent can route correctly without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit when-to-use guidance ('pass chart_type whenever the type is known'), a when-not ('suggest_chart_type already appends the chosen type's section, so a call here is only needed after the user picks a type or when switching types'), and names the fallback tool for error recovery (list_chart_types for valid ids).

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

list_chart_typesA
Read-onlyIdempotent

List all supported DGMO chart types with descriptions.

ParametersJSON Schema
NameRequiredDescriptionDefault

No parameters

TDQS

A4/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds minimal behavioral context beyond stating the content (chart types with descriptions). It does not contradict annotations, but it also does not elaborate on traits like return format or error states.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence of 6 words, conveying the essential purpose without any extraneous information. It is front-loaded and efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the simplicity of the tool (no parameters, annotations present, no output schema), the description is largely complete. It informs the agent what the tool does and what content to expect. However, it could hint at the output structure (e.g., 'returns an array of chart type objects with name and description'). Still, it is sufficient for an agent to understand the tool's purpose.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

No parameters exist, so schema coverage is 100%. The description adds context by specifying that the list includes descriptions, which adds meaning beyond the empty schema. Baseline for 0 params is 4.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description 'List all supported DGMO chart types with descriptions' clearly states the verb (list), the resource (chart types), and the scope (all supported, with descriptions). It distinguishes from sibling tools like 'suggest_chart_type' which is for recommendations, not listing.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied: use to get a list of chart types. However, there is no explicit guidance on when to use versus alternatives such as 'suggest_chart_type', nor any exclusions or prerequisites, so the description lacks clear context for selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

open_in_appA

Open a DGMO diagram in the Diagrammo desktop app (macOS only). Falls back to browser preview if the app is not installed. Pass filePath to open a saved .dgmo file directly — the app opens THAT file, so in-app edits autosave back to it (one editable source of truth, live re-render). This is the preferred path when the app is installed: write the .dgmo source first, then open it here. Omit filePath for an ephemeral diagram (sends a deep link; the app creates its own copy).

ParametersJSON Schema
NameRequiredDescriptionDefault
dgmoYesDGMO diagram markup
filePathNoAbsolute path to an already-saved .dgmo file. When set, the app opens this exact file for live editing instead of receiving a deep-linked copy.

TDQS

A4.6/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations are minimal (readOnlyHint, destructiveHint, openWorldHint). The description adds critical behavior: macOS only, fallback to browser preview, filePath autosaving and live re-render, and the distinction between ephemeral and persistent modes.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Five sentences, front-loaded with the main action and platform. Every sentence adds essential information without redundancy or filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema, but the description explains the two modes and fallback. It covers platform restriction and file persistence. Could mention installation requirement more explicitly, but 'preferred path when app is installed' implies it.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with descriptions. The description adds value by explaining that filePath opens the exact file for live editing (source of truth) and that dgmo is the markup. This enriches the basic schema definitions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description specifies the verb 'open', the resource 'DGMO diagram', and the platform 'macOS only'. It distinguishes from sibling tools like 'preview_diagram' by noting fallback behavior and file handling.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear guidance on when to use filePath (for saved files with live editing) vs omit (ephemeral diagram). It implicitly contrasts with preview_diagram as fallback, but does not explicitly list when not to use.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

preview_diagramA

Render one or more DGMO diagrams and open an HTML preview in the browser. Supports theme toggle and optional source display. For DGMO syntax call get_language_reference.

ParametersJSON Schema
NameRequiredDescriptionDefault
themeNoColor themelight
paletteNoColor palette for the page and every diagram. Given, it beats each diagram's own palette line; omitted, each diagram uses its own, and the page uses slate.
diagramsYesOne or more diagrams to preview
include_sourceNoShow DGMO source in collapsible blocks

TDQS

A3.5/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations declare readOnlyHint=false, openWorldHint=true and destructiveHint=false, so safety is partly covered. The description usefully adds that the tool opens a browser window (an observable side effect consistent with openWorldHint) and that source display is optional, which is real context. It stops short of saying whether a browser window is spawned on every call, whether the page persists, or any auth/environment requirements.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, purpose front-loaded, with no padding. The middle sentence lists features that are largely already enumerated in the schema, which is mild redundancy, so it is efficient but not flawless.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a preview tool with no output schema and full schema coverage, the description covers what the tool does and the browser-based output. It leaves unaddressed whether diagrams render inline, how multiple diagrams are laid out, and how the browser preview is surfaced to the agent, so it is nearly but not fully complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents theme, palette, diagrams, include_source and the nested dgmo/title fields, making the baseline a 3. The description's mention of 'theme toggle and optional source display' loosely maps to two parameters but adds no formatting or override semantics beyond what the schema states; palette is not mentioned at all.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

Names a specific verb+resource ('Render one or more DGMO diagrams and open an HTML preview in the browser'), which is concrete and actionable. It does not, however, distinguish itself from the sibling render_diagram, which an agent must infer from the 'HTML preview' phrasing. Without that explicit sibling contrast, it stops short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The only routing guidance is 'For DGMO syntax call get_language_reference', which points at a supporting tool rather than saying when to choose preview_diagram over render_diagram or share_diagram. Usage is only implied by the phrase 'preview'. No when-not conditions or alternatives are stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

render_diagramA
Read-onlyIdempotent

Render DGMO markup to SVG or PNG. Returns SVG text or base64 PNG image. When format is "png", also saves the image to a temp file and returns the path. For DGMO syntax call get_language_reference.

ParametersJSON Schema
NameRequiredDescriptionDefault
dgmoYesDGMO diagram markup. For syntax call get_language_reference.
themeNoColor themelight
widthNoCanvas width in px. Omit to let the diagram size itself from its content. Honoured exactly by the chart types that lay their content out into the canvas (bar, line, pie and the other data charts). A chart that sizes itself from its own nodes — org, sitemap, class, er, infra and the rest of the structured family — cannot go below its content and will return a wider canvas than asked for.
formatNoOutput formatsvg
heightNoCanvas height in px. Most chart types derive height from their content and ignore this; the data charts honour it.
paletteNoColor palette (slate, atlas, blueprint, tidewater, nord, catppuccin, tokyo-night). Given, it beats the diagram's own palette line; omitted, the diagram's own palette is used, else slate.

TDQS

A3.7/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds value beyond them by disclosing the return form (SVG text vs base64 PNG) and the non-obvious png side effect of writing a temp file and returning its path. It does not mention rate limits or error behavior, so it stops short of a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three front-loaded sentences with no filler, leading with what it renders and what it returns. The syntax pointer is duplicated verbatim in the schema's dgmo description, which is a minor redundancy rather than a flaw.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description correctly compensates by explaining exactly what comes back (SVG text or base64 PNG, plus a temp path for png). Combined with the fully documented input schema, an agent has enough to call it correctly, though sibling routing remains unaddressed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so width/height/palette semantics are already richly documented in the schema (including the content-sizing caveats). The description only adds meaning for the format parameter via its png temp-file note; theme and palette get nothing extra. Baseline 3 is appropriate when the schema carries the load.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Render DGMO markup to SVG or PNG') plus the exact return forms, so the agent knows precisely what the tool produces. It differentiates from get_language_reference for syntax help, but does not distinguish itself from siblings like preview_diagram, validate_diagram, or share_diagram.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It tells the agent the practical route for syntax ('call get_language_reference') and when a side effect occurs (png also saves a temp file), which is useful context. However, it never states when to choose this over preview_diagram or validate_diagram, leaving the main sibling-selection decision to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

share_diagramA
Read-onlyIdempotent

Generate a shareable diagrammo.app URL for a DGMO diagram. The source is compressed into the URL fragment, so nothing is uploaded and the link works for anyone who opens it; returns the URL as text. Errors when the compressed source exceeds the URL size limit (the error reports both sizes) — split or simplify the diagram, or use open_in_app / render_diagram instead. The source is not validated here; call validate_diagram first.

ParametersJSON Schema
NameRequiredDescriptionDefault
dgmoYesDGMO diagram markup

TDQS

A4.7/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (readOnly/idempotent/non-destructive/closed-world), it discloses that the source is compressed into the URL fragment, nothing is uploaded, the link works for anyone, the return is plain text, and the failure mode reports both sizes. That is substantial behavioral context the annotations alone do not convey.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tightly packed sentences with no filler; the purpose, behavior, failure mode, and prerequisite are all front-loaded in a logical order.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description still covers the return value ('returns the URL as text'), the error behavior, and the validation prerequisite, so an agent has everything needed to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Only one parameter (dgmo), and schema description coverage is 100%, so the schema already documents it. The description refers to 'the source'/'compressed source' but adds no format, encoding, or size-limit specifics beyond what the schema and error text imply — baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: 'Generate a shareable diagrammo.app URL for a DGMO diagram.' This is clearly distinct from siblings like validate_diagram, render_diagram, and open_in_app, and the agent can identify the operation without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly names alternatives and the conditions selecting them: on size-limit errors, 'split or simplify the diagram, or use open_in_app / render_diagram instead,' and it directs the agent to 'call validate_diagram first' since the source is not validated here. This is genuine when/when-not routing.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

suggest_chart_typeA

Suggest the best DGMO chart type for a user's plain-English diagram request.

Call this first when creating a new diagram: it ranks the chart types against the request and, on a confident pick, appends that type's language-reference section, so no separate get_language_reference call is needed. It is not needed when editing an existing diagram, whose first line already declares its type.

Returns one of two shapes: (1) a confident pick (high/medium) with the top match's syntax, or (2) an '⚠️ ASK THE USER' result when the choice is ambiguous or nothing matched. On an ASK-THE-USER result, present the listed candidates to the user and wait for their choice before generating, because the request alone does not settle which type they want.

ParametersJSON Schema
NameRequiredDescriptionDefault
promptYesUser's plain-English diagram request

TDQS

A4.6/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations present, the description carries the full behavioral burden and does so well: it discloses the hidden side effect of appending the language-reference section, defines both possible return shapes including the '⚠️ ASK THE USER' outcome, and prescribes agent behavior on that outcome. This is well beyond what structured fields provide.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Content is front-loaded with the core purpose and the when-to-call rule, and the result-shape and ASK-THE-USER guidance are placed last where they belong. Slightly dense, but essentially every sentence carries decision-relevant information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, and the description compensates by spelling out the two return shapes and the required agent action for each. Combined with the explicit when/when-not guidance, an agent has everything needed to call and act on this tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% for the single 'prompt' parameter, so the schema already documents it as the user's plain-English diagram request. The description adds no syntax, format, or length guidance beyond that, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource (suggest the best DGMO chart type) and scopes it to a plain-English diagram request. It clearly distinguishes itself from siblings like get_language_reference and list_chart_types by describing what it returns and why a separate reference call is unnecessary.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives an explicit call-first rule for new diagrams, states the negative case (not needed when editing an existing diagram, whose first line declares its type), and names the alternative it subsumes (get_language_reference). It also tells the agent what to do on an ambiguous result: present candidates and wait for the user.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

validate_diagramA

Validate DGMO markup without rendering. Returns structured parse errors and warnings. Much faster than render_diagram — use this to check syntax before rendering.

ParametersJSON Schema
NameRequiredDescriptionDefault
dgmoYesDGMO diagram markup to validate

TDQS

A4.5/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations exist, so the description bears full responsibility. It discloses that the tool does not render and returns structured errors/warnings, and that it is faster. While it doesn't discuss auth or rate limits, these are less critical for a validation tool. A minor omission: it could explicitly state that it does not modify data, but 'without rendering' implies no side effects.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two concise sentences, front-loads the purpose, and contains no extraneous information. Every sentence adds value.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's simplicity (one required parameter, no output schema), the description fully covers what the tool does, when to use it, and what it returns. No gaps remain.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%: the parameter 'dgmo' is described as 'DGMO diagram markup to validate'. The description adds no additional parameter-level detail beyond the schema. Per guidelines, baseline is 3 when schema coverage is high.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb 'validate' and the resource 'DGMO markup', and specifies it returns structured parse errors and warnings. It effectively distinguishes from sibling tools like render_diagram by noting it does not render.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly says to use this tool to check syntax before rendering and mentions it's much faster than render_diagram. This provides clear when-to-use guidance and contrasts with an alternative.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 3 tool updatesv0.29.10
    • Changedgenerate_report2 fields changed
      • removedInput schema / properties / palette / default
        Removed value: -"slate"
      • changedInput schema / properties / palette / description
        Previous value: -"Color palette"New value: +"Color palette for the page and every diagram. Given, it beats each diagram's own palette line; omitted, each diagram uses its own, and the page uses slate."
    • Changedpreview_diagram2 fields changed
      • removedInput schema / properties / palette / default
        Removed value: -"slate"
      • changedInput schema / properties / palette / description
        Previous value: -"Color palette"New value: +"Color palette for the page and every diagram. Given, it beats each diagram's own palette line; omitted, each diagram uses its own, and the page uses slate."
    • Changedrender_diagram2 fields changed
      • removedInput schema / properties / palette / default
        Removed value: -"slate"
      • changedInput schema / properties / palette / description
        Previous value: -"Color palette (slate, atlas, blueprint, tidewater, nord, catppuccin, tokyo-night)"New value: +"Color palette (slate, atlas, blueprint, tidewater, nord, catppuccin, tokyo-night). Given, it beats the diagram's own palette line; omitted, the diagram's own palette is used, else slate."
  2. 3 tool updatesv0.29.5
    • Changedgenerate_report1 field changed
      • changedInput schema / properties / sections / items / properties / dgmo / description
        Previous value: -"DGMO diagram markup. Color a label by appending a lowercase color name as the trailing token (e.g. \"Sales red\"); capitalize (\"Red\") to use a color word as literal text."New value: +"DGMO diagram markup. For syntax call get_language_reference."
    • Changedpreview_diagram1 field changed
      • changedInput schema / properties / diagrams / items / properties / dgmo / description
        Previous value: -"DGMO diagram markup. Color a label by appending a lowercase color name as the trailing token (e.g. \"Sales red\"); capitalize (\"Red\") to use a color word as literal text."New value: +"DGMO diagram markup. For syntax call get_language_reference."
    • Changedrender_diagram1 field changed
      • changedInput schema / properties / dgmo / description
        Previous value: -"DGMO diagram markup. Color a label by appending a lowercase color name as the trailing token (e.g. \"Sales red\"); capitalize (\"Red\") to use a color word as literal text."New value: +"DGMO diagram markup. For syntax call get_language_reference."
  3. 1 tool updatev0.29.1
    • Changedrender_diagram2 fields changed
      • addedInput schema / properties / height
        Added value: +{
        +  "description": "Canvas height in px. Most chart types derive height from their content and ignore this; the data charts honour it.",
        +  "exclusiveMinimum": 0,
        +  "type": "integer"
        +}
      • addedInput schema / properties / width
        Added value: +{
        +  "description": "Canvas width in px. Omit to let the diagram size itself from its content. Honoured exactly by the chart types that lay their content out into the canvas (bar, line, pie and the other data charts). A chart that sizes itself from its own nodes — org, sitemap, class, er, infra and the rest of the structured family — cannot go below its content and will return a wider canvas than asked for.",
        +  "exclusiveMinimum": 0,
        +  "type": "integer"
        +}
  4. 1 tool updatev0.17.0
    • Addedrender_diagram
  5. 1 tool updatev0.12.0
    • Removedrender_diagram
  6. 2 tool updatesv0.9.1
    • Changedgenerate_report1 field changed
      • changedInput schema / properties / theme / default
        Previous value: -"dark"New value: +"light"
    • Changedpreview_diagram1 field changed
      • changedInput schema / properties / theme / default
        Previous value: -"dark"New value: +"light"

TDQS

A4.1/5.0

Scored across 11 tools

Disambiguation4/5

Most tools have clearly distinct purposes: discovery (suggest_chart_type, list_chart_types, get_language_reference, get_examples), validation (validate_diagram), and output routes (render_diagram, preview_diagram, open_in_app, share_diagram). The main overlap is among the four output tools, though descriptions clearly differentiate them by destination (file/browser/app/URL). A minor risk remains that an agent conflates render_diagram with preview_diagram when just wanting to see a result.

Naming Consistency5/5

Every tool follows a clean verb_noun snake_case pattern: render_diagram, preview_diagram, generate_report, check_app_installed, get_examples, get_language_reference, list_chart_types, open_in_app, share_diagram, suggest_chart_type, validate_diagram. No mixed conventions or inconsistent verb styles.

Tool Count5/5

11 tools is well-scoped for a diagram generation/rendering server. Each tool covers a distinct step in the workflow (discovery, validation, rendering, output routing, reporting) and none feels redundant or padded.

Completeness4/5

The lifecycle is well covered: discover a chart type, fetch reference/examples, validate markup, then render/output via multiple routes plus batch reporting. Editing an existing diagram is handled implicitly through open_in_app with a filePath, but there is no explicit tool for managing or exporting saved .dgmo files, a minor gap.

Maintenance

ActivityActive
ResponsivenessSlow

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