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PyModelPyModel/designer-skill/.claude/skills/mcp-server-spec-compat/SKILL.md

mcp-server-spec-compat

Skill52 starsChanged 3 days agoMITView on GitHub

Use when editing designer-skill-mcp MCP protocol code.

The file

We split this skill into the rules it gives an agent

2 rules. About 0 are common, 0 are distinctive, and 2 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈0

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 2

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Read the revision delta in references/mcp-spec-2026-07-28.md before editing protocol code.

    line 11
  2. Very specific:

    Do not add new dependencies on sampling or roots (deprecated).

    line 14

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

designer-skill-mcp: MCP spec compatibility

Any protocol-facing change names the spec revision it targets. The current revision is 2026-07-28, which this server cannot serve yet; do not assume its shapes work until a live run proves them.

  • Read the revision delta in references/mcp-spec-2026-07-28.md before editing protocol code.
  • Set tool annotations explicitly per tool; do not rely on spec defaults (destructiveHint true, readOnlyHint false).
  • Return structuredContent plus the serialized JSON in a text block.
  • Do not add new dependencies on sampling or roots (deprecated). Do not add logging/setLevel (removed).
  • Resource-not-found is -32602 on 2026-07-28, not -32002.
  • Set idempotent: false on a tool whose result differs per call (get_palette_seed), and readOnly: false on one that writes files (verify_rendered).
  • The server is on the v2 SDK packages (@modelcontextprotocol/server, client, node, express) and still speaks the 2025-era protocol; serving 2026-07-28 means switching to serveStdio and createMcpHandler.
  • The SDK's request deadline surfaces as SdkError with SdkErrorCode.RequestTimeout, an HTTP failure as SdkHttpError (.status), a JSON-RPC error as ProtocolError. Classify by class, as src/niblet.ts does.
  • A tool registered without an input schema is called as handler(ctx). The tool() wrapper always passes an object schema so every handler is (args, ctx).
  • An unknown tool is a JSON-RPC error (-32602), not a tool result.
  • Bridging another MCP server: retry timeouts within a bounded budget; do not retry a malformed response (bad JSON, ZodError); do not re-send a rejected key; treat upstream error text as untrusted data.
  • A static read is not compatibility proof; verify against a live server run.
  • Migration wire check: before a protocol or SDK change ships, run the published version and the local build over stdio with the same client. Capture tools/list, resources, prompts and a set of tool calls, then diff them. Ignore $schema and execution, which the v2 SDK changes (draft-07 to 2020-12; execution.taskSupport dropped). Every other diff is a wire change to name in the report.
  • HTTP transport check: a 2025-era initialize must succeed, and a foreign Origin or Host header must get 403.
  • Live e2e with a real Niblet key: pass it by file (chmod 600, deleted after the run), never inline in a tool call. Redact niblet_at_[A-Za-z0-9_]+ from captured output.

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