mcp-migration

name

mcp-migration

description

Diagnose and carry out the migration of an MCP server to the 2026-07-28 specification — the revision that made the transport stateless, formalized OAuth 2.1, and deprecated the logging, sampling, and roots capabilities. Use this skill whenever someone mentions migrating, upgrading, or checking an MCP server against the 2026-07-28 spec; asks whether their MCP server still works, is "ready", or will break; mentions the stateless transport model, Mcp-Session-Id, or OAuth 2.1 for MCP; or is debugging an MCP server that stopped working after a spec or SDK bump. Also use it when someone asks you to review or audit MCP server code for compatibility, even if they don't name the spec date.

MCP 2026-07-28 migration

The 2026-07-28 revision is a refactor, not a version bump. Five things this checker looks for break existing servers:

1. The transport is stateless. The initialize/notifications/initialized handshake and the Mcp-Session-Id header are gone from this revision. Every request carries its own protocol version and client capabilities in _meta. This does not mean deleting the handshake. A server "wishing to support both legacy clients … and modern clients MAY implement both behaviors" and picks its semantics from how each request opens — so the goal is to add the modern path, and retire the legacy one on the schedule your own clients dictate. Removing it for compliance breaks every v1 client for no gain.
2. OAuth 2.1 is formalized for remote servers: a protected MCP server acts as an OAuth 2.1 resource server and MUST implement RFC 9728 protected-resource metadata.
3. logging, sampling, and roots are deprecated — still functional, with a twelve-month minimum window, but new implementations should not adopt them.
4. The TypeScript SDK moved to v2 under new package names. @modelcontextprotocol/sdk is the v1 line and stops at 1.30.0. v2 ships as @modelcontextprotocol/server + @modelcontextprotocol/client (plus /core and an /express, /fastify or /hono adapter).
5. The Python SDK moved to v2 under the same package name. The official PyPI package remains mcp, while mcp.server.fastmcp.FastMCP becomes mcp.server.MCPServer. A <2 constraint or the old import is a v1 signal.

The revision changed more than the checker covers: server/discover is now mandatory, all results carry a required resultType, the GET stream and resources/subscribe are replaced by subscriptions/listen, ping and logging/setLevel are gone, SSE resumability is removed, and Mcp-Method / Mcp-Name headers are required. A clean checker run is not a migration. Read the changelog before declaring a server done.

Do not tell anyone to upgrade @modelcontextprotocol/sdk to ^2. That package has never published a 2.x — the migration is to the new package names above. There is an official codemod, and it is a separate package:

npx @modelcontextprotocol/codemod@latest v1-to-v2 .

The other Tier 1 SDKs moved differently: C# to a 2.x major, Go to a 1.x minor. Check the actual package before advising a version.

Work in this order: diagnose, triage, remediate, re-verify. The diagnosis step is scripted so it gives the same answer every time — resist the urge to skip it and eyeball the code, because the rule ids it emits are what the remediation guidance keys off.

Step 1 — Diagnose

Run the bundled checker. It needs nothing but Node — no install step.

# Scan a repository (the richest signal; this is the one to start with)
node scripts/mcpcheck.mjs --source /path/to/the/server

# Probe a running endpoint
node scripts/mcpcheck.mjs https://example.com/mcp

# Probe a local dev server (disables the SSRF guard)
node scripts/mcpcheck.mjs --local http://localhost:3000/mcp

# Machine-readable, if you want to process the findings
node scripts/mcpcheck.mjs --source . --json

Run both the source scan and a live probe when a server is actually running. They see different things and neither is a superset of the other:

	Source scan	Live probe
Sees	code, package.json, Python manifests, file:line	both protocol eras, headers, advertised capabilities, OAuth posture
Finds	MCP001–005, MCP007/MCP009/MCP010 (SDK lines)	MCP001–006, MCP008, MCP101/102
Needs	a checkout	a reachable endpoint

Exit codes: 0 no critical findings · 1 at least one critical · 2 inconclusive (unreachable, blocked, or nothing to scan).

Step 2 — Triage before you touch anything

The source scan is regex-based. It greps for the patterns that correlate with each hazard, which means it reports signals, not proof. Two consequences worth internalising before you start editing:

• False positives are normal. A file that merely mentions initialize in a comment, or a variable coincidentally named sessionId, will be flagged. The checker's own source flags itself for all five code rules, because the rules file contains the very strings it searches for.
• A clean scan is not a guarantee. Session state can be spelled in ways the patterns don't catch — a Map keyed by something the code calls clientKey, for instance.

So read each finding at its file:line, decide whether it is real, and say so explicitly before changing anything. A short triage table is a good artefact to produce here: rule, location, real or false positive, and why.

Findings are graded: 100 minus 30 per critical and 15 per warning. info findings (MCP1xx) cost nothing — they record compatibility choices the spec permits, such as a dual-era server still answering initialize, so that a report can distinguish "still accepts legacy" from "only accepts legacy". Treat the letter grade as a headline for humans, not as the thing to optimize. Fixing the criticals matters far more than the score moving from D to B.

Step 3 — Remediate

Read references/remediation.md for the per-rule guidance. It is organised by rule id, so go straight to the sections your findings named rather than reading it end to end.

Sequence matters. Do it in this order, because later steps depend on earlier ones:

1. The SDK finding first — MCP007 for TypeScript, MCP009 for Python, MCP010 for Rust. Doing this before the code changes means you refactor against the API you are going to keep, instead of refactoring twice. For MCP007, move to the v2 packages and run the TypeScript codemod. For MCP009, move mcp to 2.x and follow the official Python migration guide (FastMCP → MCPServer is the first import change). For MCP010, upgrade to rmcp 3.x or rust-mcp-sdk 2.x (both speak spec 2026-07-28). For tower-mcp, enable the protocol-2026-07-28 feature. The remaining errors point at the architectural work.
2. MCP002 (session state) — the deepest change, and the one most likely to surface hidden design assumptions.
3. MCP001 (legacy-only) — add the modern request path and server/discover; largely mechanical once state is gone. Keep the legacy handshake serving alongside it unless you have decided, as a product call, to drop v1 clients.
4. MCP003/004/005 (deprecated capabilities) — removals, each one localised. These are warning, not critical, and the deprecation window is at least twelve months. If the migration is already large, deferring them is a defensible call — say so rather than silently skipping them.
5. MCP006 (OAuth posture) — deployment-facing; independent of the rest.

After each step, re-run the scan. Watching one rule at a time go quiet is a much better signal than a single run at the end where you can't tell which change fixed what.

Step 4 — Verify

Re-run both the source scan and, if a server is running, the live probe. Then check the things the scanner structurally cannot see:

• Does the server still behave correctly when two consecutive requests land on different instances? This is the real test of statelessness, and no static scan can answer it. Run two instances behind anything that round-robins, or restart the process between requests.
• Do the tests still pass, and do they still cover the paths you changed?
• If you removed sampling, has the model-calling responsibility actually moved to the client, or has it just been deleted?

Reporting back

Close with a short summary in this shape — it is what someone reviewing the migration needs, and nothing more:

## Migration summary
- Before: <grade> — <n> findings (<n> critical)
- After:  <grade> — <n> findings (<n> critical)

## Changed
- <rule id>: <what was changed, where>

## Dismissed as false positives
- <rule id> at <file:line>: <why it was not a real hazard>

## Still open
- <anything deliberately not fixed, and why>

The "dismissed" section is the one people skip and later regret. If you decided a finding was noise, the reasoning needs to survive past the end of the session.

A note on the spec itself

The findings link to the canonical spec at https://modelcontextprotocol.io/specification/2026-07-28. When a fix involves an exact API signature or a precise header name, check it there rather than trusting a remembered detail — this skill describes the shape of each change, not a frozen copy of the specification.