copilot-acp-mcp-bridge

Run GitHub Copilot CLI behind a local MCP server.

If your client speaks MCP and Copilot speaks ACP, this bridge sits in the middle and gets out of the way.

Status: Copilot CLI ACP is in public preview. The protocol surface may change. Pin your Copilot CLI version and test after upgrades.

Codex / Claude Code / MCP client
            ↓
     copilot-acp-mcp-bridge
            ↓
   copilot --acp --stdio

Example:

codex mcp add copilot -- node /absolute/path/to/copilot-acp-mcp-bridge.js

quickstart

git clone https://github.com/oijkn/copilot-acp-mcp-bridge.git
cd copilot-acp-mcp-bridge
codex mcp add copilot -- node /absolute/path/to/copilot-acp-mcp-bridge.js

If you want to call it by command name instead of path:

npm link
codex mcp add copilot -- copilot-acp-mcp-bridge

If you want to pin a default model for the whole bridge process:

COPILOT_ARGS_JSON='["--model","gpt-5.2"]' \
codex mcp add copilot -- node /absolute/path/to/copilot-acp-mcp-bridge.js

If you need a specific working directory:

COPILOT_ACP_BRIDGE_CWD=/home/you/project \
codex mcp add copilot -- node /absolute/path/to/copilot-acp-mcp-bridge.js

With the linked CLI:

COPILOT_ACP_BRIDGE_CWD=/home/you/project \
codex mcp add copilot -- copilot-acp-mcp-bridge

why this exists

GitHub Copilot CLI already speaks ACP. MCP clients speak MCP. Those two pieces do not talk to each other directly.

This repo fills that gap. It turns MCP tools/call requests into ACP session/prompt calls and sends the result back over stdio. If you want to use Copilot from an MCP client without writing your own adapter first, this is the missing piece.

what you get

One local stdio bridge, no npm install step
Persistent sessions for conversational use
Fresh one-shot sessions with freshSession: true
A hard tool block with allowTools: false
Basic diagnostics through copilot_session_status and copilot_reset_session

how it works

MCP client (Codex, etc.)
  └── MCP stdio ──> copilot-acp-mcp-bridge
                      └── ACP stdio ──> copilot --acp --stdio
                                          └── Copilot's own MCP servers
                                              (Docker, GitHub, AWS, Playwright, ...)

The bridge translates tools/call ask_copilot (MCP) into session/prompt (ACP) and streams updates back. Copilot loads its own MCP config automatically in ACP mode, so its full toolset is available without extra configuration.

requirements

Node.js >= 18
GitHub Copilot CLI >= 1.0.9, authenticated (copilot login)
An MCP client that can run a local stdio server (codex mcp add, Claude Code, etc.)

No npm dependencies. The bridge uses only Node.js built-ins.

tools

`ask_copilot`

Send a task to Copilot. Returns Copilot's response plus a telemetry block (tool calls, plan, usage) when INCLUDE_TELEMETRY_IN_OUTPUT=true (default).

| Argument | Type | Default | Description | |---|---|---|---| | prompt | string | required | Task or question for Copilot | | context | string | — | System or background text prepended to the prompt | | freshSession | boolean | false | Spawn a fresh Copilot process for this call only | | allowTools | boolean | true | If false, hard-block all tool use: every ACP session/request_permission is answered with cancelled, regardless of permissionPolicy | | model | string | — | Optional Copilot CLI model name. Applies at the process/session level, not as an ACP per-prompt switch |

Unknown arguments are rejected with MCP error -32602. There is no silent fallback.

Model semantics:

model configures the Copilot process used for the call or session
freshSession: true + model starts a disposable Copilot process with --model <name>
the first persistent call may also set model; that choice is then fixed until copilot_reset_session
a later persistent call that requests a different model is rejected with -32602
effectiveModel is an observed model value read from the ACP session/new response when Copilot exposes it

Session modes:

Persistent (default): One Copilot process, one ACP session, reused across calls. Copilot retains context between prompts. Calls are serialized.
Fresh (freshSession: true): A new Copilot process is spawned for the call and killed when it completes. No context from previous calls. Use for isolated analysis, one-shot tasks, or anything where a clean slate matters.

`copilot_session_status`

Returns the current state of the persistent session: sessionId, sessionAgeMs, promptCount, agentInfo, persistentConfiguredModel, effectiveModel, modelSource, availableModels, activePrompt.

persistentConfiguredModel: the model this bridge configured for the persistent session
effectiveModel: the observed model returned by ACP session/new, when available
modelSource: where the configured model came from (default, env:copilot_args_json, ask_copilot:first_persistent_call, or ask_copilot:fresh_session)
availableModels: models advertised by Copilot in session/new, when available

`copilot_reset_session`

Kills the persistent Copilot process and resets the session. The next ask_copilot call starts fresh.

| Argument | Type | Description | |---|---|---| | reason | string | Optional log note |

environment variables

| Variable | Default | Description | |---|---|---| | COPILOT_BIN | copilot | Path to the Copilot CLI binary | | COPILOT_ARGS_JSON | [] | Extra args to pass to copilot --acp --stdio as JSON array | | COPILOT_ACP_BRIDGE_CWD | process.cwd() | Working directory for the ACP session | | CHAIRMAN_CWD | — | Legacy alias for COPILOT_ACP_BRIDGE_CWD | | STARTUP_TIMEOUT_MS | 15000 | Timeout for ACP handshake | | PROMPT_TIMEOUT_MS | 300000 | Timeout for a single prompt | | CANCEL_GRACE_MS | 10000 | Grace period after session/cancel | | PERMISSION_POLICY | first | first, prefer-allow, or cancel | | PREFERRED_PERMISSION_OPTION_ID | — | Auto-select a specific permission option by ID | | AUTO_AUTH_METHOD_ID | — | Attempt ACP auth automatically if Copilot requires it | | EAGER_START | false | Start Copilot immediately on bridge startup instead of on first call | | INCLUDE_TELEMETRY_IN_OUTPUT | true | Append tool calls, plan, and session metadata to MCP response | | INCLUDE_USAGE_IN_OUTPUT | true | Include token usage in telemetry block | | LOG_LEVEL | info | error, warn, info, debug | | ACP_SESSION_CONFIG_OPTIONS_JSON | — | Extra config options passed to session/new | | ACP_SESSION_MODES_JSON | — | Session modes passed to session/new | | COPILOT_ACP_MCP_SERVERS_JSON | — | MCP servers to inject into session/new (JSON array) | | COPILOT_ACP_MCP_SERVERS_FILE | — | Path to a JSON file with MCP server list |

COPILOT_ARGS_JSON can already pin a process-wide model, for example ["--model","gpt-5.2"].

running the tests

# Unit tests (no Copilot required)
BRIDGE=./copilot-acp-mcp-bridge.js bash test-bridge.sh unit

# Full test suite (requires authenticated Copilot CLI)
BRIDGE=./copilot-acp-mcp-bridge.js \
COPILOT_ACP_BRIDGE_CWD=/your/project \
bash test-bridge.sh

If you linked the package locally, this works too:

npm run test:unit

known limitations

ACP session cwd is fixed at session/new. There is no per-call working directory override. Multi-repo use requires restarting the bridge or calling copilot_reset_session.
allowTools: false blocks permissions at the bridge level, but cannot prevent Copilot from reasoning about tools internally. It is a protocol-level guard, not a model-level constraint.
On prompt timeout, the bridge sends ACP session/cancel to Copilot, then surfaces the timeout back to the MCP client as an error.
Copilot CLI ACP is in public preview. Pin your CLI version (copilot --version) and check the Copilot CLI docs after upgrades.
Multi-session (one session per repo or per call) is not implemented. All persistent calls share one session.
model is implemented with process/session-level semantics. The bridge does not do per-prompt model switching inside an already running persistent ACP session.

tested environment

| Component | Version | |---|---| | Node.js | 22.x | | Copilot CLI | 1.0.9 | | MCP protocol | 2024-11-05 | | ACP protocol | 1 |

repository metadata

GitHub description: Run GitHub Copilot CLI behind a local MCP server through ACP.

Suggested topics: mcp, model-context-protocol, acp, agent-client-protocol, github-copilot, copilot-cli, nodejs, stdio

Suggested social preview:

use docs/logo.svg on a dark background
subtitle: MCP bridge for GitHub Copilot CLI

license

Apache-2.0 — see LICENSE.

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