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Free MCP server that renders bar/line/area charts to SVG from structured data. Open twin of the paid x402-gated dataviz HTTP API.
Single tool with well-structured schema and clear description. Input parameters are properly typed with enums and descriptions. Tool name 'render_chart' is action-oriented and unambiguous. Description (194 chars) explains what, when, and why. Schema uses Zod with proper validation (minItems=1, enum constraints). Error handling returns structured responses with isError flag. Main gaps: no output schema documentation, no pagination/limits guidance, no tool annotations (readOnlyHint), and description lacks dependency hints or recovery guidance.
Render a bar, line, or area chart from structured data and return it as an SVG string. Free, unauthenticated MCP tool — the open twin of the paid x402-gated dataviz HTTP API (https://x402-dataviz-poc.theliminalguy.workers.dev/chart), same renderer, no payment required.
Output schema not documented. LLMs cannot predict the SVG string structure or plan downstream processing. Add explicit output schema documentation in tool definition.
No tool annotations (readOnlyHint). Tool is read-only and safe to retry, but LLM has no signal. Add readOnlyHint: true to tool metadata.
Description lacks recovery guidance for common errors. If rendering fails (e.g., invalid data structure), description should hint at validation steps or alternative approaches.
Error message format is generic ('render failed: <message>'). Should categorize errors (invalid input vs rendering engine failure) and provide actionable guidance.
| Scored | Grade | Overall | Spec posture | Rubric |
|---|---|---|---|---|
| 2026-09-23 | C | 62 | 2026-07-28+ | v2 |
No guidance on SVG size limits or performance constraints. Large datasets may produce oversized SVGs. Add description note about data size recommendations.