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drawspec

by nuncaeslupus
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python

Render a drawspec document to SVG, PNG or text

render_document
Read-onlyIdempotent

Draws a ready drawspec document as SVG, PNG, or text, so you can show diagrams inline in Markdown, as images, or in terminals.

Instructions

Draw the document. Use it when it is ready to show; while still fixing errors, validate_document returns just the verdict. Returns one content block by format: svg (default) self-contained SVG text, safe inline in Markdown; png a base64 image/png block (needs the server's drawspec[png] extra, slowest); text plain text for a code block, only for kinds with a text form. width/height override the document's size; with text, width is cells per line and height and theme are ignored. Local, deterministic, writes nothing. Refusals are error results with JSON text {"ok": false, "error": "DocumentError", "message": "...", "violations": [{"pointer": "/edges/0/to", "message": "..."}]}: error is e.g. DocumentError or FitError, pointer is RFC 6901 (empty for the whole document), and violations is never empty.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
scaleNopng only: pixels per SVG unit (default 2).
themeNoA bundled theme name (accent, blueprint, compartment, default, wheel) or a path to a `.toml` theme file on the server's disk, e.g. `blueprint`. Omit for `default`.
widthNoOverride the document's width, e.g. `640`. With format `text`, the most terminal cells a line may take (default 80, or 100 for `lanes` and `sequence`).
formatNosvg (default), png, or text: the diagram as plain text for a code block or a terminal, for the kinds files, tree, sequence, gantt, timeline, board, stack, rag, meter, flow, states, lanes.
heightNoOverride the document's height (ignored with format `text`).
charsetNotext only: box-drawing characters, or ASCII only (default unicode).
documentYesA drawspec document as a JSON object (not a string or a path), e.g. `{"version": 1, "kind": "flow", "nodes": [...], "edges": [...]}`. `list_kinds` names the 36 values `kind` may take, `get_example` returns the smallest valid document of one, and `get_schema` returns its fields (the whole format is published at https://nuncaeslupus.github.io/drawspec/schema/drawspec-v1.schema.json).
backgroundNopng only: the page the drawing is on (default light).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changedv0.3.4
    • changedInput schema / properties / document / description
      Previous value: -"A drawspec document, as JSON. `list_kinds` names the 36 values `kind` may take, `get_example` returns the smallest valid document of one, and `get_schema` returns its fields (the whole format is published at https://nuncaeslupus.github.io/drawspec/schema/drawspec-v1.schema.json)."New value: +"A drawspec document as a JSON object (not a string or a path), e.g. `{\"version\": 1, \"kind\": \"flow\", \"nodes\": [...], \"edges\": [...]}`. `list_kinds` names the 36 values `kind` may take, `get_example` returns the smallest valid document of one, and `get_schema` returns its fields (the whole format is published at https://nuncaeslupus.github.io/drawspec/schema/drawspec-v1.schema.json)."
    • changedInput schema / properties / height / description
      Previous value: -"Override the document's height."New value: +"Override the document's height (ignored with format `text`)."
    • changedInput schema / properties / theme / description
      Previous value: -"A bundled theme name or a path to a theme file. Omit for the default."New value: +"A bundled theme name (accent, blueprint, compartment, default, wheel) or a path to a `.toml` theme file on the server's disk, e.g. `blueprint`. Omit for `default`."
    • changedInput schema / properties / width / description
      Previous value: -"Override the document's width. With format `text`, the most terminal cells a line may take (default 80, or 100 for `lanes` and `sequence`)."New value: +"Override the document's width, e.g. `640`. With format `text`, the most terminal cells a line may take (default 80, or 100 for `lanes` and `sequence`)."
  2. Addedv0.3.3

TDQS

A4.8/5.0
Behavior5/5

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

Annotations already cover read-only/idempotent/non-destructive, but the description adds substantial operational context: per-format return types, that PNG needs a server extra and is slowest, that text-only applies to certain kinds, that width becomes cells-per-line with text while height/theme are ignored, and a full JSON shape for refusal errors including RFC 6901 pointers. This goes well beyond 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.

Conciseness4/5

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

Purpose and the alternative are front-loaded in the first sentence, followed by dense but non-redundant detail. It is long for a single paragraph and could be split, though each clause carries distinct 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 fully covers what comes back per format and how errors are surfaced, and it points to `list_kinds`/`get_example`/`get_schema` for document construction. Nothing an agent needs 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?

Schema coverage is 100%, so the baseline is 3, but the description adds cross-parameter interactions the schema does not state — that `height` and `theme` are ignored under `text`, and that `width` means cells-per-line in that mode. It doesn't add much beyond that, so it stops short of 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 concrete verb+resource ("Draw the document") and immediately distinguishes itself from the sibling `validate_document`, noting the latter "returns just the verdict" while this renders output. An agent can tell the two apart without opening either 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 the condition for use ("when it is ready to show") and the alternative to use in the other case (`validate_document` while still fixing errors). This is a clear when/when-not/alternative routing statement.

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

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