Muhammad Zakir RamadhanandSisyphus
6452299a45
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
134 lines
4.7 KiB
Markdown
134 lines
4.7 KiB
Markdown
# MCP
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[Model Context Protocol](https://modelcontextprotocol.io) servers contribute tools. Configure
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them in `~/.shiro-neko/config.json` and they appear alongside the builtins.
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## Configuration
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```json
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{
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"mcpServers": {
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"fs": {
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"command": "npx",
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"args": ["-y", "@modelcontextprotocol/server-filesystem", "."]
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},
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"db": {
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"command": "python",
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"args": ["-m", "my_mcp_server"],
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"env": { "DATABASE_URL": "postgres://localhost/dev" },
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"cwd": "/home/you/tools"
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},
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"api": {
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"url": "http://localhost:3000/mcp",
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"type": "http",
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"headers": { "Authorization": "Bearer local-dev-token" }
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}
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}
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}
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```
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**stdio** servers take `command`, and optionally `args`, `env`, `cwd`. The process is spawned
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at startup and closed on exit. `env` is merged over the inherited environment, so a server
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inherits your `PATH` unless you replace it.
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**Remote** servers take `url`, and optionally `type` (`http` or `sse`, default `http`) and
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`headers`.
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A token in `headers` sits in `config.json` in plain text, same as `apiKey`. For anything beyond
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a local dev token, prefer a stdio server that reads its own credential from the environment.
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## Startup cost
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Servers connect **in parallel**, so the slowest one sets how long startup takes rather than the
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sum of them. `npx -y some-server` re-resolves the package on each launch; installing it and
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calling the binary directly is usually the difference between a noticeable wait and none.
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`--no-mcp` skips them all, which is also the quickest way to tell whether a slow start is MCP
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or something else.
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## Naming
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Tools arrive as `mcp__<server>__<tool>`. A server named `fs` exposing `read_file` becomes
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`mcp__fs__read_file`.
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The namespace is not cosmetic. Two servers both exposing `search` would otherwise silently
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shadow each other, and the model would call one believing it was the other.
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## Approval
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**Every MCP tool requires approval on every call.** They are third-party code with unknown
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side effects, so they are treated like `bash` rather than like `read_file`. `a` whitelists
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one tool for the session.
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`--yolo` skips these prompts, as it does for the builtins. Plugin guards still apply.
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## Failure handling
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A server that fails to start is reported and the session continues:
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```
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shiro-neko 0.1.0-beta.4 openai/gpt-5 session 0193ab2c
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mcp: 4 tools
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mcp db failed: spawn python ENOENT
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```
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Nothing else is lost — the other servers still load, the builtins still work. A missing
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Python interpreter should not stop you from editing a file.
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`--no-mcp` skips them all.
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## Inspecting
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`/tools` lists everything offered this turn, MCP tools included. The system prompt describes
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them as a group:
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```
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- mcp__api__query, mcp__fs__read_file: from MCP servers, named mcp__<server>__<tool>.
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Each needs approval; read its own description before calling.
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```
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Their individual descriptions come from the server, so that is what the model reads before
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calling one.
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## Cost
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Each tool adds its name, description, and JSON schema to every request. The built-ins average
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548 bytes; MCP tools vary with how verbose the server's schema is. A server exposing twenty
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tools costs roughly 2,750 tokens per turn, sent whether or not the model uses any of them.
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MCP tools are **not** covered by `toolSets` — that budget only governs the built-ins. There is
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no per-server switch either, so the choice is a server or no server, and `--no-mcp` for all of
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them. If one exposes many tools you never use, a narrower server is worth finding or writing.
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`/tools` shows the count both ways:
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```
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tools
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26 offered this turn of 26 registered
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```
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A gap between the two numbers means a tool set or a read-only agent variant is withholding
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something. MCP tools never appear in that gap.
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## Writing a server
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Any MCP-compliant server works. A minimal stdio one needs three methods: `initialize`,
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`tools/list`, and `tools/call`. The test suite includes one at
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`test/fixtures/mcp-stub.ts` — about 50 lines, and useful as a starting point.
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The suite runs it as a **real subprocess** rather than mocking the transport, because the parts
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that break in practice are the handshake and the framing, and a mock asserts neither.
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## Debugging a server
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A server that starts but returns nothing useful is the harder case. In order of speed:
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1. `/tools` — did the tools arrive at all? A server with no tools is a `tools/list` problem.
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2. `shiro -p "call mcp__x__y with ..." --json --yolo` — the exact `tool-call` input and
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`tool-result` output, one JSON object per line.
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3. Run the server by hand: `echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | your-server`.
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If that is wrong, nothing above it can be right.
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For an HTTP server, `curl -X POST $URL -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'`
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answers the same question without shiro in the way.
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