Render Mermaid with Line9 layout in your assistant.
Scored across 3 tools
Each tool has a clearly distinct role: list diagrams, fetch a specific diagram, or render arbitrary Mermaid source. Even though get_diagram and render_diagram both produce rendered output, the former retrieves published diagrams while the latter processes user-supplied Mermaid, so there is no real ambiguity.
All tools follow a clean snake_case verb_noun pattern: get_diagram, list_diagrams, render_diagram. The singular/plural noun difference is conventional and does not create inconsistency.
Three tools is the right size for a read-only diagram connector. Each tool covers a necessary step—discover, retrieve, render—and none feel redundant or missing for the declared scope.
The read-only workflow is well covered: list, get, and render form a natural pipeline. Write/publish operations are intentionally excluded and consistently communicated, but the server name 'Line9' could lead agents to expect at least create or update functionality, making it a minor expectation gap rather than a dead end.
Fetch a published diagram's current Mermaid source by name or slug, and show it rendered. The returned source is stamped with the diagram's identity — keep the line9: frontmatter block when you edit it so that Line9 recognises the diagram when it is opened and published there instead of creating a new one. Requires Line9 sign-in. This connector cannot publish or save. To publish, the user opens the diagram in Line9 (the open_url link) and publishes there — not with the Line9 CLI.
| Name | Required | Description | Default |
|---|---|---|---|
| diagram | Yes | Diagram name, slug, or trailing public_ref. |
| Name | Required | Description |
|---|---|---|
| svg | No | |
| path | No | |
| plan | No | |
| error | No | |
| width | No | |
| config | No | |
| height | No | |
| source | No | |
| status | Yes | |
| diagram | No | |
| controls | No | |
| diagrams | No | |
| open_url | No | |
| warnings | No | |
| signed_in | No | |
| truncated | No | |
| watermark | No | |
| edge_count | No | |
| node_count | No | |
| orientation | No | |
| render_mode | No | |
| stop_reason | No | |
| diagram_type | No | |
| engine_version | No | |
| schema_version | Yes | |
| fallback_reason | No | |
| mermaid_version | No |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Even with readOnlyHint and idempotentHint annotations, the description adds substantial behavioral detail: the returned source carries a line9 frontmatter identity block that must be preserved, the diagram is recognized on open/publish in Line9, auth is required, and the connector is write-incapable. This goes well beyond the annotation surface.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Four focused sentences, with the core action first and every subsequent sentence adding necessary context (frontmatter handling, auth, save/publish limitations). No filler or repetition.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given one fully-schema-covered parameter, an existing output schema, and safety annotations, the description provides everything needed for correct use: auth, source behavior, identity preservation, and limitations. No critical guidance is missing.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The single parameter is fully covered by the schema description ('Diagram name, slug, or trailing public_ref'). The tool description restates only 'name or slug' and adds no additional parameter format, examples, or disambiguation, so it neither compensates for nor improves on the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description names a concrete action and resource: fetching a published diagram's current Mermaid source by name or slug and showing it rendered. It is clearly not a tautology, but it does not explicitly distinguish itself from the sibling tools list_diagrams and render_diagram beyond the implied source-vs-list/render split.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It gives useful context about prerequisites and boundaries (requires Line9 sign-in; cannot publish or save; publishing happens via the open_url link, not the CLI). However, it never directly says when to choose this tool over render_diagram or list_diagrams, so sibling routing is left to inference.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
List the diagrams published in the user's Line9 workspace(s): name, visibility, version, last update and permalink. Use it to find a diagram before get_diagram. Requires Line9 sign-in.
| Name | Required | Description | Default |
|---|---|---|---|
| limit | No | Maximum rows to return (1–100; default 50). | |
| query | No | Case-insensitive substring of the diagram name. |
| Name | Required | Description |
|---|---|---|
| svg | No | |
| path | No | |
| plan | No | |
| error | No | |
| width | No | |
| config | No | |
| height | No | |
| source | No | |
| status | Yes | |
| diagram | No | |
| controls | No | |
| diagrams | No | |
| open_url | No | |
| warnings | No | |
| signed_in | No | |
| truncated | No | |
| watermark | No | |
| edge_count | No | |
| node_count | No | |
| orientation | No | |
| render_mode | No | |
| stop_reason | No | |
| diagram_type | No | |
| engine_version | No | |
| schema_version | Yes | |
| fallback_reason | No | |
| mermaid_version | No |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate read-only, idempotent, non-destructive. The description adds the requirement for Line9 sign-in and specifies the fields returned, providing extra behavioral context. No contradictions with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is two concise sentences, front-loading the action and fields, then adding the usage guideline. No wasted words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple list tool with two optional parameters and an output schema, the description covers purpose, usage, and auth requirement. It does not detail response format, but the output schema likely covers that, so it's adequately complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, with both `limit` and `query` fully described. The description does not add parameter-level detail beyond what the schema provides, so baseline of 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool lists diagrams in the user's Line9 workspace, enumerates the fields returned (name, visibility, version, last update, permalink), and explicitly differentiates from `get_diagram` by saying it's used to find a diagram before fetching it. This distinguishes it from siblings.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description explicitly says to use it to find a diagram before `get_diagram`, providing a clear use case. However, it does not contrast with `render_diagram` or mention when not to use it, leaving some ambiguity about alternative workflows.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Render Mermaid source with Line9's layout engine. Call this whenever you write or change Mermaid and the user should see the result. Flowcharts and sequence diagrams get Line9's layout; other Mermaid kinds are rendered with Mermaid's own layout and flagged as such. Returns a short verdict — kind, size, warnings, or a parse error with its line and column — plus an "Open in Line9" link. On a parse error, fix the named line and call again. Assistants that support MCP Apps show the diagram in a panel; there, do not paste the SVG or repeat the source in your reply. In an assistant with no panel (a terminal or editor), reply with the verdict line and the open_url link — that link is the only way the user sees the diagram. Write flowcharts as flowchart LR unless the user asks for top-to-bottom; chat panels are wide and short. No sign-in needed; renders carry a small Line9 mark unless the user is signed in to Line9 Pro. Set theme, orientation, spacing and legend in the source itself (line9: frontmatter; flowchart LR), never as arguments. This connector cannot publish or save. To publish, the user opens the diagram in Line9 (the open_url link) and publishes there — not with the Line9 CLI.
| Name | Required | Description | Default |
|---|---|---|---|
| plan | No | Opaque plan from a previous result (widget use). A hint only: skips the solve when it still fits the source. | |
| source | Yes | Mermaid source. Optional YAML frontmatter is honoured — set it in the source, never as arguments: `title`, and a nested `line9:` block with `theme` (one of `boardroom`, `linen`, `blueprint`), `scale: { node, spacing }` and `flowchart: { legend: on | off }`. The flowchart direction directive is also honoured. Maximum 100000 characters. |
| Name | Required | Description |
|---|---|---|
| svg | No | |
| path | No | |
| plan | No | |
| error | No | |
| width | No | |
| config | No | |
| height | No | |
| source | No | |
| status | Yes | |
| diagram | No | |
| controls | No | |
| diagrams | No | |
| open_url | No | |
| warnings | No | |
| signed_in | No | |
| truncated | No | |
| watermark | No | |
| edge_count | No | |
| node_count | No | |
| orientation | No | |
| render_mode | No | |
| stop_reason | No | |
| diagram_type | No | |
| engine_version | No | |
| schema_version | Yes | |
| fallback_reason | No | |
| mermaid_version | No |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool read-only, non-destructive and idempotent; the description goes well beyond that by disclosing layout differences for diagram kinds, parse-error details (line/column), the Open in Line9 link, panel vs terminal rendering, sign-in/branding behavior, and the impossibility of publishing/saving. None of this contradicts the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Dense but efficient: the core purpose and trigger come first, followed by output, failure handling, client differences, and constraints, with no filler or repeated schema text. The length is justified by the number of behavioral nuances an agent must know before invoking this tool.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the complexity — custom layout, frontmatter options, panel vs terminal output, parse-error recovery, auth/branding, and publish limitations — the description is complete. It even covers the failure retry loop ('fix the named line and call again'), and the return-value burden is covered by the output schema plus the explicit verdict summary.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
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 adds real value by explaining that `plan` is an opaque hint from a prior result and by prohibiting style/theme arguments ('set ... in the source itself, never as arguments'). It also clarifies what frontmatter in `source` controls, which goes beyond the schema's property names.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
States a specific verb and resource — 'Render Mermaid source with Line9's layout engine' — and immediately distinguishes rendering from the get/list siblings. It also specifies what the call produces (verdict, link, panel rendering), so an agent can tell exactly what the tool does.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicit trigger condition: 'Call this whenever you write or change Mermaid and the user should see the result.' It also states clear exclusions ('cannot publish or save', 'not with the Line9 CLI') and gives branch instructions for panel vs no-panel clients, so both tool choice and follow-up action are unambiguous.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
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