Native MCP and codemode

Sources: https://pi.dev/docs/latest/mcp, https://pi.dev/docs/latest/cli, and Pi 0.99.2 packages/mcp / built-in extension source.

Pi 0.99.2 includes MCP, codemode, and tool search as built-in extensions. These are separate from the optional pi-mcp-adapter package; its configuration and commands are in pi-mcp-adapter.md.

Configure native servers

pi mcp add filesystem -- npx -y @modelcontextprotocol/server-filesystem .
pi mcp list

Commands mutate global ~/.pi/agent/mcp.json by default; --local / -l uses trusted project .pi/mcp.json. A project entry replaces the same-named global entry. The example installs/executes a third-party server and is illustrative; inspect/pin it before deployment.

{
  "mcpServers": {
    "docs": {
      "url": "https://mcp.example.com/mcp",
      "headers": { "Authorization": "Bearer ${DOCS_TOKEN}" },
      "description": "Search and read documentation",
      "exposure": "codemode",
      "timeout": 60
    }
  }
}

Use command plus argv args, optional env and cwd for stdio. Use url, optional headers, oauth, or provider-token auth for HTTP. type may be stdio, http, or streamable-http; legacy SSE is rejected. timeout is seconds, default 60; progress resets it. enabled: false disables a native server. This differs from adapter disabled: true and requestTimeoutMs.

env/header values support ${VAR} interpolation and whole-value !command. command itself is an executable, never a shell command string. Avoid putting credentials in project files.

/mcp manages connections and exposure. CLI pi mcp add|remove|list|login|logout uses the built-in implementation without loading extensions. pi mcp list connects enabled servers and exits 1 for invalid entries or failures. Run /reload after external config edits.

Authentication

HTTP OAuth runs through /mcp login <server> or pi mcp login <server> and stores refreshable credentials in ~/.pi/agent/mcp-auth.json. Remote users can paste the final redirect URL. Registered clients use oauth.clientId, optional clientSecret, callbackPort/callbackUrl, scope, and clientName; the callback must be an HTTP loopback URL matching the server registration. An explicit Authorization header takes precedence over automatic OAuth.

Pi 0.99.2 also accepts auth: { provider: "<provider>" } to read a provider's current /login token on each request. It is allowed only in global config or extension registration, requires HTTPS except loopback, and should only target a service authorized to receive that provider credential. OAuth flows were not executed in this audit.

Exposure and execution

Default codemode exposure hides definitions until scripts discover them. deferred uses tool_search; direct declares tools immediately; hidden makes them unreachable. codemode-deferred aliases codemode. toolExposure overrides individual original names or * patterns: exact match wins, otherwise first matching pattern.

Names are mcp__<server>__<tool> with non-alphanumeric/non-underscore characters normalized to _. Same-server tool collisions gain hash suffixes; server names differing only in - versus _ are rejected. Discover actual names instead of guessing.

Enabled servers connect in the background at session start. First prompts wait only for direct-tool servers (up to 10s); discovery/tool use waits for the required servers. The model sees a compact mcp_servers system-prompt section; codemode's tool description does not expand as these servers connect.

Illustrative codemode body:

const hits = await searchTools("documentation", { limit: 5 });
text(hits);
text(await describeNamespace("mcp__docs"));

Use tools.<discovered_name>(args) after inspecting its declaration. Scripts run in QuickJS and have ALL_TOOLS, searchTools, describeTool, describeNamespace, text, image, store/load, exit, and a top-level return. Optional first line: // @options: {"max_output_tokens": 2000, "timeout_ms": 60000}. No deadline is set by default. store persists JSON only after a successful script and follows the session branch.

Enable codemode without MCP through defaultTools: ["+codemode"]. CLI --tools replaces the complete list and does not accept +/- deltas. codemode.mode: "only" hides other declarations while keeping callable tools. QuickJS limits the script environment; underlying tools still have the Pi process's permissions.

MCP script calls resolve to a full CallToolResult, including content, structuredContent, and isError. An error result resolves with isError rather than necessarily throwing. Direct model output truncates text over 20KB and includes a spill path; scripts receive the complete result. Nested calls pass Pi validation/permission hooks and report parentToolCallId.

Resources and SDK

list_mcp_resources({ server?, cursor? }), list_mcp_resource_templates(...), and read_mcp_resource({ server, uri }) cover resources. With server, listing returns one page and nextCursor; without it, Pi collects every server. MCP App UI resources are omitted because native Pi does not render them. Tool calls are not retried automatically; resource reads/listing retry once on transient HTTP failures.

Extensions register native servers with pi.registerMcpServer(name, config) and withdraw with pi.unregisterMcpServer(name). File config wins name conflicts. SDK hosts must explicitly add createMcpExtension, createCodemodeExtension, and createToolSearchExtension and bind extensions. Emit session_shutdown before bare-session disposal (or await runtime disposal) to close transports; see sdk.md.

An extension claiming /mcp replaces native session MCP. Current adapter 4.0 detects native Pi and uses /mcp-adapter instead, so both can coexist with separate files. Never duplicate one server in both owners' config unless two connections are intended.