Fixes and recipes for Model Context Protocol clients and servers: startup errors, transports, auth, config.
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Symptom claude mcp get <name shows ⏸ Pending approval (run claude to approve) for a server defined in the project's .mcp.json. Environment and tested versions Debian GNU/Linux 13…
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Symptom The server reads ./data.json and gets ENOENT: no such file or directory, open './data.json' (cwd is /), or a relative script path in args gives Error: Cannot find module…
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Symptom claude mcp login dcr fails with SDK auth failed: Incompatible auth server: does not support dynamic client registration. Environment and tested versions Debian GNU/Linux…
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Symptom claude mcp add mem node .../dist/index.js memory path /tmp/x.json fails with error: unknown option ' memory path'. Environment and tested versions Debian GNU/Linux 13…
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Symptom The server is missing from claude mcp list, which warns: Skipped — MCP server "remote" has a "url" but no "type"; add "type": "http" (or "sse" / "ws") to this entry.…
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Symptom The remote server receives an empty Authorization header and answers 401; mcp remote then falls back to OAuth and fails (Incompatible auth server: does not support dynamic…
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Symptom A client that can only spawn local commands can't use an https://.../mcp server. Putting the URL in "command" gives spawn http://127.0.0.1:44309/mcp ENOENT. Environment…
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Symptom The server reports that DEMO API KEY is not set, even though it's exported in the shell that launched the client. Environment and tested versions Debian GNU/Linux 13…
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Symptom A long tool call fails with MCP error 32001: Request timed out. Environment and tested versions Debian GNU/Linux 13 (trixie) x86 64, node 20.19.2, npm 11.21.1; test server…
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Symptom A Python MCP server launched with "command": "uvx" never starts; the client reports spawn uvx ENOENT. Environment and tested versions Debian GNU/Linux 13 (trixie) x86 64,…
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Symptom The client logs Unexpected token 'S', "Server sta"... is not valid JSON, and again on every tool call that logs something. Environment and tested versions Debian GNU/Linux…
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Symptom A stdio MCP server configured with "command": "npx" never starts; the client reports spawn npx ENOENT. Node was installed with nvm. Environment and tested versions Debian…
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