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Real numbers from this tool, line by line.
Six lines that a US platform team's MCP server still ships stopped being protocol on 28 July 2026 - and the server still starts up clean.
That is the whole trap. The 2026-07-28 revision of the Model Context Protocol did not rename those calls or soften them into warnings. It removed them. A server written against 2025-06-18 or 2025-11-25 keeps answering old clients perfectly, and breaks the first morning a client upgrades. Nothing goes red in your editor, because none of it is a syntax error.
Here is what a working server looked like in June, and what each line is now:
| Still in your repo | What 2026-07-28 says |
|---|---|
InitializeRequestSchema | removed - implement server/discover; version rides in _meta |
Mcp-Session-Id header | removed - mint your own handle, pass it as a tool argument |
PingRequestSchema | removed - nothing replaces it |
resources/subscribe | replaced by subscriptions/listen |
roots/list (server-initiated) | replaced by InputRequiredResult (MRTR) |
McpError(-32002) | McpError(-32602) |
The second trap is that your assistant cannot help you find them. It was trained before 28 July 2026. Ask it for an MCP server today and it will write InitializeRequestSchema, "type": "sse" and -32002, and if you ask whether that is current it will tell you yes. The tool that produced the debt is not the tool that clears it.
And the config files carry their own version of this. "type": "sse" is the HTTP+SSE transport, deprecated since protocol 2025-03-26 and now formally Deprecated under the new feature-lifecycle policy, which sets a minimum twelve-month window before removal. Roots, Sampling and Logging entered that same window on 28 July 2026 - so the earliest they can disappear is 28 July 2027. That is your migration budget, and it is already six weeks spent.
MCP 2026 Migration Lint is 27 rules that read the file you have open - .vscode/mcp.json, .mcp.json, claude_desktop_config.json, .cursor/mcp.json, or JS/TS/Python server source - and put a line number, the change it comes from, and the replacement on each finding. It runs offline; nothing is uploaded.
{
"mcpServers": {
"github": {
"type": "sse",
"headers": { "Mcp-Session-Id": "abc123" },
"env": { "GITHUB_TOKEN": "ghp_9f2k1JqR7sT4vW0xYz" }
}
}
}Four findings on those eight lines: the key mcpServers shows nothing in VS Code, which reads servers; "type": "sse" is the deprecated transport; Mcp-Session-Id was removed outright; and the token is a literal credential in a file that usually gets committed.
The file you have open is free - all 27 rules, no key, no account. Doing it by hand instead means reading the changelog and mapping every removal across every file yourself; freelance senior software engineers publish an average of $101 an hour. The paid tier does not give better answers, it changes the scale: the whole repository in one pass, an exported report, and CI output so a removed RPC cannot be merged back in. $29 once, seven-day full refund.
15 seconds — what it actually does
Questions people ask
What does MCP 2026 Migration Lint actually do?
It reads an MCP config file or MCP server source and marks every line that the 2026-07-28 revision of the Model Context Protocol removed or deprecated. Each finding carries a line number, the change it comes from, and the replacement to write instead. Twenty-seven rules, run entirely on your machine, offline.
Who is this for?
Developers and platform teams who ship MCP servers, and anyone maintaining .vscode/mcp.json, .mcp.json, claude_desktop_config.json or .cursor/mcp.json in a repository. It is most useful to teams whose MCP server was written against the 2025-06-18 or 2025-11-25 revisions and has not been touched since.
Why can't I just ask an AI assistant to check it?
Because the assistant is the source of the error. Models trained before 28 July 2026 still generate InitializeRequestSchema, ping handlers, Mcp-Session-Id headers and error code -32002, and will confirm they are correct when asked. This extension holds the current removal list and does not negotiate with a chat window.
What is free and what costs money?
Free, with no key and no account: all twenty-seven rules on the file you have open or on the lines you select, with the fix for each. That finishes the file. The paid tier changes scale, not answer quality: the whole repository in one pass, an exported CSV/JSON/HTML report, and CI output that fails the build.
What would this cost me otherwise?
Doing it by hand means reading the 2026-07-28 changelog and mapping every removal across each config and server file yourself. Freelance senior software engineers publish an average of $101 per hour (contractrates.fyi, 2026, from 584 submissions). The extension is $29 once,.
Why not just ask ChatGPT or another AI chat?
A general AI chat answers from training data with a cutoff date, cannot read your repository and names no rule version. MCP Server Lint - 2026 spec migration checks the file you open against 27 rules from a rule set dated 2026-09-20, and points at the exact line with the fix. For a filing, an audit or a client you need that dated result on your own files.
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