MCP Protocol Conformance

Part of the StudioMeyer MCP Stack — Built in Mallorca 🌴 · ⭐ if you use it

mcp-protocol-conformance

Conformance test harness for Model Context Protocol servers. Validates JSON-RPC 2.0 wire compliance, spec-version handshake, transport behaviour, OAuth 2.1 PKCE, tool schemas, capability advertisement, smoke roundtrip, and annotation hygiene against MCP spec 2024-11-05, 2025-03-26, 2025-06-18, and the current **stable** revision **2025-11-25** (experimental `tasks`, structured tool output, JSON Schema 2020-12 default, tool `title`/`icons`).

This is a Foundation build of the StudioMeyer MCP Factory: every other Factory build runs through this harness before promotion (npm publish, marketplace submit, upstream PR).

A note from us

We have been building tools and systems for ourselves for the past two years. The fact that this repo is small and has few stars is not because it is new. It is because we only just decided to share what we have built. It is not a fresh experiment, it is a long story with a recent commit.

We love building things and sharing them. We do not love social media tactics, growth hacks, or chasing stars and followers. So this repo is small. The code is real, it gets used, issues get answered. Judge for yourself.

If it helps you, sharing, testing, and feedback help us. If it could be better, an issue is more useful. If you build something with it, tell us at hello@studiomeyer.io. That genuinely makes our day.

From a small studio in Palma de Mallorca.

Install

npm install --save-dev mcp-protocol-conformance

The package ships both a CLI (mcp-conformance) and a TypeScript library entry (import ... from "mcp-protocol-conformance").

CLI usage

Run against a stdio server

mcp-conformance run \
  --target stdio \
  --cmd node \
  --cmd-arg dist/server.js \
  --spec 2025-06-18 \
  --suite all \
  --format terminal

Run against an HTTP server (Streamable HTTP, 2025-03-26+)

mcp-conformance run \
  --target http \
  --url https://memory.studiomeyer.io/mcp \
  --header "Authorization:Bearer ${TOKEN}" \
  --spec 2025-06-18 \
  --suite full \
  --format json --out report.json

Run only a subset of suites

mcp-conformance run --target stdio --cmd ./server --spec 2025-06-18 \
  --suite jsonrpc,version,schema

Compare two manifests

mcp-conformance compare \
  --expected manifests/v1.json \
  --actual   manifests/v2.json

Assert no breaking changes between two reports

mcp-conformance assert-no-breaking \
  --baseline reports/main.json \
  --current  reports/pr-42.json

Exit codes: 0 clean, 1 failures, 2 invocation error.

Library usage

import {
  runFullSuite,
  generateReport,
} from "mcp-protocol-conformance";

const report = await runFullSuite(
  { kind: "stdio", cmd: "node", args: ["dist/server.js"] },
  "2025-06-18",
  { suite: "all" },
);

console.log(generateReport(report, "terminal"));
if (report.status === "fail") process.exit(1);

MCP server usage

The harness is itself an MCP server. Start it over stdio and any MCP client can call its 12 tools:

node dist/server.js

Tools (all read-only, all destructiveHint: false):

#	Tool	Purpose
1	runJsonRpcCompliance	JSON-RPC 2.0 error-code matrix + response-envelope (result/error mutual exclusivity)
2	runSpecVersionAssertion	Verify advertised protocolVersion
3	runTransportSuite	Transport-layer ping + session-id
4	runOauthPkceFlow	OAuth 2.1 PKCE S256 (mock-AS or real-tenant)
5	runToolSchemaValidation	inputSchema (+ 2025-11-25 outputSchema / title) is valid JSON-Schema
6	runCapabilityIntrospection	initialize.capabilities matches behaviour (+ 2025-11-25 tasks)
7	runRoundtripSmoke	One tools/call per advertised tool
8	runAnnotationsAudit	readOnlyHint / destructiveHint hygiene
9	runFullSuite	All suites + summary
10	generateReport	Render JUnit / JSON / terminal
11	compareManifests	Diff two tool manifests
12	assertNoBreakingChanges	Diff two FullReports

Compatibility matrix

	2024-11-05	2025-03-26	2025-06-18	2025-11-25
jsonrpc	yes	yes	yes	yes
version (handshake)	yes	yes	yes	yes
transport (stdio)	yes	yes	yes	yes
transport (http)	n/a	yes	yes	yes
oauth (mock)	n/a	yes	yes	yes
oauth (real)	n/a	yes	yes	yes
schema	yes	yes	yes	yes
capability	yes	yes	yes	yes
smoke	yes	yes	yes	yes
annotations	warn-only	warn-only	yes	yes
tasks (capability)	n/a	n/a	n/a	yes
tool title/output	n/a	n/a	n/a	warn-only

yes = suite runs and produces actionable results. n/a = capability not in spec; suite skips automatically. warn-only = suite runs but the spec does not formally require the feature.

The 2026-07-28 RC (stateless core, SEP-2575/2567) is intentionally not here — it ships final on 2026-07-28; conformance for it lands in a later release against the final SDK.

Integration in Factory builds

In every Factory build's package.json:

{
  "scripts": {
    "factory:conformance": "mcp-conformance run --target stdio --cmd 'node dist/server.js' --spec 2025-06-18 --suite full"
  }
}

In CI:

- run: npm run factory:conformance

Spec references

• JSON-RPC 2.0: https://www.jsonrpc.org/specification
• MCP 2024-11-05: https://modelcontextprotocol.io/specification/2024-11-05
• MCP 2025-03-26: https://modelcontextprotocol.io/specification/2025-03-26
• MCP 2025-06-18: https://modelcontextprotocol.io/specification/2025-06-18
• MCP 2025-11-25: https://modelcontextprotocol.io/specification/2025-11-25
• RFC 7636 (PKCE): https://datatracker.ietf.org/doc/html/rfc7636

About StudioMeyer

StudioMeyer is an AI and design studio based in Palma de Mallorca, working with clients worldwide. We build custom websites and AI infrastructure for small and medium businesses. Production stack on Claude Agent SDK, MCP and n8n, with Sentry, Langfuse and LangGraph for observability and an in-house guard layer.

License

MIT — Copyright (c) 2026 Matthias Meyer (StudioMeyer)