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OpenClaw ACP Bridge

This document describes how the OpenClaw ACP (Agent Client Protocol) bridge works, how it maps ACP sessions to Gateway sessions, and how IDEs should invoke it.

Overview

openclaw acp exposes an ACP agent over stdio and forwards prompts to a running OpenClaw Gateway over WebSocket. It keeps ACP session ids mapped to Gateway session keys so IDEs can reconnect to the same agent transcript or reset it on request.

Key goals:

  • Minimal ACP surface area (stdio, NDJSON).
  • Stable session mapping across reconnects.
  • Works with existing Gateway session store (list/resolve/reset).
  • Safe defaults (isolated ACP session keys by default).

Bridge Scope

openclaw acp is a Gateway-backed ACP bridge, not a full ACP-native editor runtime. It is designed to route IDE prompts into an existing OpenClaw Gateway session with predictable session mapping and basic streaming updates.

Compatibility Matrix

ACP area Status Notes
initialize, newSession, prompt, cancel Implemented Core bridge flow over stdio to Gateway chat/send + abort.
listSessions, slash commands Implemented Session list works against Gateway session state; commands are advertised via available_commands_update.
loadSession Partial Rebinds the ACP session to a Gateway session key and replays stored user/assistant text history. Tool/system history is not reconstructed yet.
Prompt content (text, embedded resource, images) Partial Text/resources are flattened into chat input; images become Gateway attachments.
Session modes Partial session/set_mode is supported and the bridge exposes initial Gateway-backed session controls for thought level, tool verbosity, reasoning, usage detail, and elevated actions. Broader ACP-native mode/config surfaces are still out of scope.
Session info and usage updates Partial The bridge emits session_info_update and best-effort usage_update notifications from cached Gateway session snapshots. Usage is approximate and only sent when Gateway token totals are marked fresh.
Tool streaming Partial tool_call / tool_call_update events include raw I/O, text content, and best-effort file locations when Gateway tool args/results expose them. Embedded terminals and richer diff-native output are still not exposed.
Per-session MCP servers (mcpServers) Unsupported Bridge mode rejects per-session MCP server requests. Configure MCP on the OpenClaw gateway or agent instead.
Client filesystem methods (fs/read_text_file, fs/write_text_file) Unsupported The bridge does not call ACP client filesystem methods.
Client terminal methods (terminal/*) Unsupported The bridge does not create ACP client terminals or stream terminal ids through tool calls.
Session plans / thought streaming Unsupported The bridge currently emits output text and tool status, not ACP plan or thought updates.

Known Limitations

  • loadSession replays stored user and assistant text history, but it does not reconstruct historic tool calls, system notices, or richer ACP-native event types.
  • If multiple ACP clients share the same Gateway session key, event and cancel routing are best-effort rather than strictly isolated per client. Prefer the default isolated acp:<uuid> sessions when you need clean editor-local turns.
  • Gateway stop states are translated into ACP stop reasons, but that mapping is less expressive than a fully ACP-native runtime.
  • Initial session controls currently surface a focused subset of Gateway knobs: thought level, tool verbosity, reasoning, usage detail, and elevated actions. Model selection and exec-host controls are not yet exposed as ACP config options.
  • session_info_update and usage_update are derived from Gateway session snapshots, not live ACP-native runtime accounting. Usage is approximate, carries no cost data, and is only emitted when the Gateway marks total token data as fresh.
  • Tool follow-along data is best-effort. The bridge can surface file paths that appear in known tool args/results, but it does not yet emit ACP terminals or structured file diffs.

How can I use this

Use ACP when an IDE or tooling speaks Agent Client Protocol and you want it to drive a OpenClaw Gateway session.

Quick steps:

  1. Run a Gateway (local or remote).
  2. Configure the Gateway target (gateway.remote.url + auth) or pass flags.
  3. Point the IDE to run openclaw acp over stdio.

Example config:

openclaw config set gateway.remote.url wss://gateway-host:18789
openclaw config set gateway.remote.token <token>

Example run:

openclaw acp --url wss://gateway-host:18789 --token <token>

Selecting agents

ACP does not pick agents directly. It routes by the Gateway session key.

Use agent-scoped session keys to target a specific agent:

openclaw acp --session agent:main:main
openclaw acp --session agent:design:main
openclaw acp --session agent:qa:bug-123

Each ACP session maps to a single Gateway session key. One agent can have many sessions; ACP defaults to an isolated acp:<uuid> session unless you override the key or label.

Zed editor setup

Add a custom ACP agent in ~/.config/zed/settings.json:

{
  "agent_servers": {
    "OpenClaw ACP": {
      "type": "custom",
      "command": "openclaw",
      "args": ["acp"],
      "env": {}
    }
  }
}

To target a specific Gateway or agent:

{
  "agent_servers": {
    "OpenClaw ACP": {
      "type": "custom",
      "command": "openclaw",
      "args": [
        "acp",
        "--url",
        "wss://gateway-host:18789",
        "--token",
        "<token>",
        "--session",
        "agent:design:main"
      ],
      "env": {}
    }
  }
}

In Zed, open the Agent panel and select “OpenClaw ACP” to start a thread.

Execution Model

  • ACP client spawns openclaw acp and speaks ACP messages over stdio.
  • The bridge connects to the Gateway using existing auth config (or CLI flags).
  • ACP prompt translates to Gateway chat.send.
  • Gateway streaming events are translated back into ACP streaming events.
  • ACP cancel maps to Gateway chat.abort for the active run.

Session Mapping

By default each ACP session is mapped to a dedicated Gateway session key:

  • acp:<uuid> unless overridden.

You can override or reuse sessions in two ways:

  1. CLI defaults
openclaw acp --session agent:main:main
openclaw acp --session-label "support inbox"
openclaw acp --reset-session
  1. ACP metadata per session
{
  "_meta": {
    "sessionKey": "agent:main:main",
    "sessionLabel": "support inbox",
    "resetSession": true,
    "requireExisting": false
  }
}

Rules:

  • sessionKey: direct Gateway session key.
  • sessionLabel: resolve an existing session by label.
  • resetSession: mint a new transcript for the key before first use.
  • requireExisting: fail if the key/label does not exist.

Session Listing

ACP listSessions maps to Gateway sessions.list and returns a filtered summary suitable for IDE session pickers. _meta.limit can cap the number of sessions returned.

Prompt Translation

ACP prompt inputs are converted into a Gateway chat.send:

  • text and resource blocks become prompt text.
  • resource_link with image mime types become attachments.
  • The working directory can be prefixed into the prompt (default on, can be disabled with --no-prefix-cwd).

Gateway streaming events are translated into ACP message and tool_call updates. Terminal Gateway states map to ACP done with stop reasons:

  • complete -> stop
  • aborted -> cancel
  • error -> error

Auth + Gateway Discovery

openclaw acp resolves the Gateway URL and auth from CLI flags or config:

  • --url / --token / --password take precedence.
  • Otherwise use configured gateway.remote.* settings.

Operational Notes

  • ACP sessions are stored in memory for the bridge process lifetime.
  • Gateway session state is persisted by the Gateway itself.
  • --verbose logs ACP/Gateway bridge events to stderr (never stdout).
  • ACP runs can be canceled and the active run id is tracked per session.

Compatibility

  • ACP bridge uses @agentclientprotocol/sdk (currently 0.15.x).
  • Works with ACP clients that implement initialize, newSession, loadSession, prompt, cancel, and listSessions.
  • Bridge mode rejects per-session mcpServers instead of silently ignoring them. Configure MCP at the Gateway or agent layer.

Testing

  • Unit: src/acp/session.test.ts covers run id lifecycle.
  • Full gate: pnpm build && pnpm check && pnpm test && pnpm docs:build.

Related Docs

  • CLI usage: docs/cli/acp.md
  • Session model: docs/concepts/session.md
  • Session management internals: docs/reference/session-management-compaction.md