OpenCode ACP Skill

Drive an OpenCode CLI session over the Agent Client Protocol (ACP).

When to use this skill

Use it when the calling agent must:

• Start an OpenCode process and talk to it programmatically (not as a human at a terminal).
• Drive multi-turn coding sessions, including prompt → stream → cancel loops.
• Resume a previous OpenCode session by ID.
• Detect and trigger OpenCode auto-updates.

Do not use it for direct file editing, one-off shell commands, or any task that does not require the Agent Client Protocol.

Quick Reference

The calling agent must map these generic names to its own platform (Hermes, Clawdbot, etc.). See README.md for the mapping table.

Protocol Rules

• Wire format: JSON-RPC 2.0, newline-delimited (one JSON object per line, each frame terminated by \n). Not LSP Content-Length.
• Direction: requests are agent → OpenCode (stdin). Responses and server notifications arrive on stdout.
• IDs: every request carries an integer id; the calling agent increments monotonically starting at 0. Notifications have no id and never produce a response.
• Sessions are opaque: the sessionId returned by session/new is the only reference; treat it as a string.
• Capabilities: declare fs.readTextFile, fs.writeTextFile, and terminal in the initialize handshake.

Standard Workflow

1. Start

terminal(
  command: "opencode acp --cwd /path/to/project",
  background: true,
  workdir: "/path/to/project"
)

Save the returned processId. All subsequent frames go through it.

2. Initialize

{"jsonrpc":"2.0","id":0,"method":"initialize","params":{
  "protocolVersion":1,
  "clientCapabilities":{
    "fs":{"readTextFile":true,"writeTextFile":true},
    "terminal":true
  },
  "clientInfo":{
    "name":"opencode-acp-control",
    "title":"OpenCode ACP Control",
    "version":"0.3.0"
  }
}}

Expect result.protocolVersion: 1.

3. Create session

{"jsonrpc":"2.0","id":1,"method":"session/new","params":{
  "cwd":"/path/to/project",
  "mcpServers":[]
}}

Save result.sessionId (e.g. "sess_abc123").

4. Send prompt

{"jsonrpc":"2.0","id":2,"method":"session/prompt","params":{
  "sessionId":"sess_abc123",
  "prompt":[{"type":"text","text":"List the TypeScript files in this repo."}]
}}

5. Stream the response

Poll stdout every ~2s until a response arrives whose id matches your request and whose result.stopReason is set. While polling you will also receive notifications:

{"jsonrpc":"2.0","method":"session/update","params":{...}}

Collect them in order — they make up the agent's streamed output.

6. Cancel (when needed)

{"jsonrpc":"2.0","method":"session/cancel","params":{"sessionId":"sess_abc123"}}

No response is sent for a cancel — it is a notification.

7. Handle permission requests

OpenCode asks for confirmation before running shell commands or editing files by sending a server-to-client request:

{"jsonrpc":"2.0","id":12,"method":"requestPermission","params":{
  "sessionId":"sess_abc123",
  "toolCall":{"toolCallId":"call_1","status":"pending",
              "title":"bash","rawInput":{"command":"npm install"},"kind":"bash"}
}}

Prompt the user, then respond with the matching id:

{"jsonrpc":"2.0","id":12,"result":{"reply":"once"}}      // allow once
{"jsonrpc":"2.0","id":12,"result":{"reply":"always"}}    // allow for the session
{"jsonrpc":"2.0","id":12,"result":{"reply":"reject"}}    // deny

State to Track

For each OpenCode instance the calling agent holds:

Polling and Timeout Strategy

• Interval: 2 seconds between process.poll calls.
• Maximum wait per prompt: 5 minutes (150 polls). Treat as timeout beyond.
• An empty poll response means the agent is still thinking — keep polling.
• A malformed line on stdout is logged and skipped; do not abort on parse errors alone.

Resume Session

1. terminal("opencode session list", workdir: "<project>") returns a table of {id, updated, messages}.

2. ask_user to pick one.

3. terminal("opencode acp --cwd <project>", background:true) to restart.

4. initialize (id=0).

5. session/load with the chosen id, plus cwd and mcpServers:

   {"jsonrpc":"2.0","id":1,"method":"session/load","params":{
     "sessionId":"sess_abc123","cwd":"/path/to/project","mcpServers":[]
   }}
   

OpenCode streams the full conversation history back through session/update notifications.

Failure Modes

Update Procedure

OpenCode auto-updates on restart. To check and trigger an update:

1. terminal("opencode --version") → current version.

2. web_fetch("https://github.com/sst/opencode/releases/latest") → latest tag in the redirect URL.

3. Compare versions. If newer:

   • process(action:"list") to find every running opencode acp process.
   • process.kill(processId) for each.
   • Wait ~2 seconds.
   • terminal("opencode acp", background:true) to restart and trigger the auto-download.

4. Verify with opencode --version again. If still old, fall back to a manual install (review the installer script before piping curl | bash):

   curl -fsSL https://opencode.ai/install | bash
   

Implementation Notes

• cwd must be absolute; normalize before sending.
• Serialize JSON deterministically (sort_keys=True if possible) to make log diffs stable.
• Treat stderr separately from stdout if your platform exposes it — ACP frames never appear on stderr.
• When the host agent runs in a sandbox, cwd must be inside the sandbox; the ACP server inherits the calling agent's filesystem access.
• Session ids are opaque strings; do not parse them.
• The first initialize after a process start must complete before any other request — JSON-RPC servers reject out-of-order calls.

See also

• examples/acp_demo.py — runnable end-to-end demo with --dry-run and --no-prompt modes.
• README.md — quick start and tool-platform mapping.
• CHANGELOG.md — release notes.
• ACP spec: https://agentclientprotocol.com/llms.txt
• OpenCode: https://opencode.ai