@spences10/pi-mcp

Bring your MCP servers into Pi as first-class agent tools. pi-mcp discovers configured servers, exposes their tools safely, and keeps large MCP responses manageable through Pi’s context sidecar integration.

Installation

pi install npm:@spences10/pi-mcp

Local development from this monorepo:

pnpm --filter @spences10/pi-mcp run build
pi install ./packages/pi-mcp
# or for one run only
pi -e ./packages/pi-mcp

Configuration

The extension loads MCP server definitions from mcp.json files in global and project locations. For compatibility with Claude Code, a project-level .mcp.json is also accepted when that project has no mcp.json. If both files exist, mcp.json takes precedence and the extension warns that .mcp.json was ignored.

A typical project mcp.json (or compatible .mcp.json) looks like:

{
	"mcpServers": {
		"sqlite": {
			"command": "npx",
			"args": ["-y", "mcp-sqlite-tools", "./data.db"]
		}
	}
}

Global MCP config is loaded automatically. Project-local mcp.json is untrusted by default because stdio servers can spawn local commands. Interactive runs prompt before loading it; headless runs skip it unless MY_PI_MCP_PROJECT_CONFIG=allow is set. Allow-once mode loads project MCP tools but suppresses rich tool descriptions and schema prose so untrusted server metadata cannot act as prompt injection. Use MY_PI_MCP_PROJECT_CONFIG=trust to trust and remember the current repo until the selected project config file's hash changes and expose full metadata, or MY_PI_MCP_PROJECT_CONFIG=skip to force-disable project MCP config.

Stdio MCP servers receive a restricted child-process environment by default: baseline shell variables plus explicit per-server env values. Use MY_PI_MCP_ENV_ALLOWLIST=NAME,OTHER_NAME or the shared MY_PI_CHILD_ENV_ALLOWLIST to pass selected ambient variables through.

Servers are not connected at session startup by default. Use /mcp connect <server> or set MY_PI_MCP_EAGER_CONNECT=1 to connect and discover tools eagerly.

Keep mcp.json portable by putting my-pi activation rules in a separate policy file. Global policy lives at ~/.pi/agent/mcp-policy.json; project policy lives at .pi/mcp-policy.json. Project policy is loaded only when project MCP config passes the project trust decision. It may further restrict a global policy, but cannot replace or widen one; when both scopes define a server, both policies must match. A server with no policy keeps the default behavior. A server with an activateWhen policy is skipped entirely unless at least one criterion matches the current cwd or GitHub remote.

{
	"servers": {
		"pm-platform": {
			"activateWhen": {
				"githubOrg": ["spences10"],
				"githubRepo": ["spences10/my-pi"],
				"cwdPrefix": ["/home/scott/repos/my-pi"]
			}
		}
	}
}

Server tools are registered as Pi tools using this naming format:

mcp__<server>__<tool>

For example, a sqlite server tool named execute_read_query becomes:

mcp__sqlite__execute_read_query

Constrained sampling

MCP tools opt into Pi's strict JSON Schema sampling only when their server-owned schema is a conservative, fully required object schema. Eligible schemas may contain nested objects, arrays, primitive types, enums, constants, and descriptions. Every object node must explicitly set additionalProperties: false; the schema is never rewritten.

Schemas remain on normal tool calling when they contain optional properties, defaults, union types, non-object roots, missing or open additionalProperties, references, composition keywords such as anyOf, or other unsupported keywords. This avoids turning provider differences into MCP failures; strict: "prefer" also lets Pi fall back when the active provider or model lacks strict-tool support.

The /mcp server detail view reports only aggregate eligible/normal counts and safe reason codes. It never displays schema content or tool arguments as part of these diagnostics.

Commands

/mcp                         # open the TUI server manager
/mcp manage                  # same as /mcp
/mcp list
/mcp enable <server>
/mcp disable <server>
/mcp connect [server|all]
/mcp backup                  # backup global + project MCP config
/mcp restore [backup-file]   # restore from picker or filename/path
/mcp profile list
/mcp profile save [name]
/mcp profile load [name] [global|project]
/mcp profiles                # saved profile list and actions

Use /mcp to open a modal home menu for server management, read-only summaries, backups, and profiles. Toggles update the current session and persist a disabled/enabled flag in the winning mcp.json entry. Backups are written under ~/.pi/agent/mcp-backups/ and restore global/project MCP config exactly as captured after modal confirmation. Profiles are saved under ~/.pi/agent/mcp-profiles/ as reusable merged server sets that can be saved with a modal input and loaded into global or project MCP config after modal confirmation.

What it does

• reads MCP server config
• connects to stdio or HTTP MCP servers on demand
• performs the MCP initialize handshake
• discovers tools via tools/list
• registers each discovered MCP tool with Pi
• updates Pi's active tools as servers connect or disconnect; current Pi applies those changes to the next provider request in the same agent run
• forwards model tool calls to the MCP server
• disconnects idle connected servers after 15 minutes by default (MY_PI_MCP_IDLE_TIMEOUT_MS=0 disables this globally; per-server idle_timeout_ms overrides it)
• truncates oversized MCP tool text output to the first 50 KiB or 2,000 lines
• when @spences10/pi-context is enabled, stores oversized full output in the local SQLite context sidecar and returns a searchable source id
• otherwise saves truncated full output to a local /tmp/my-pi-mcp-output-*.txt file so it can be inspected with read or rg
• cleans up server processes on session shutdown

Using from a custom harness

import mcp from '@spences10/pi-mcp';

// pass `mcp` as an ExtensionFactory to your Pi runtime

my-pi imports this package directly and enables it as the built-in MCP extension.

Development

Package scripts build transitive workspace dependencies first, then run local tools through Vite+ with vp exec.

pnpm --filter @spences10/pi-mcp run check
pnpm --filter @spences10/pi-mcp run test
pnpm --filter @spences10/pi-mcp run build

License

MIT