Friday · Use

Editors and ACP

Friday speaks the Agent Client Protocol (ACP), the protocol editors such as Zed and JetBrains IDEs use to run coding agents. friday acp starts the Go engine on standard input and output; the editor draws the conversation, Friday does the work.

This documentation is in English.

On this page

Zed
Other editors
What an editor gets
The extension
Troubleshooting

Zed

Add Friday under agent_servers in Zed's settings.json (or Settings → AI → Add Agent → Add Custom Agent):

json

{
  "agent_servers": {
    "Friday": {
      "command": "friday",
      "args": ["acp"],
      "env": {}
    }
  }
}

Keys come from Friday's own settings (friday settings), so the env block can stay empty. Put a key there only to use a different one inside Zed, for example "env": { "ARCHYMEDES_PROVIDER": "groq" }.

Session flags work after acp: ["acp", "--auto"] starts sessions in auto mode, ["acp", "--provider", "anthropic", "--model", "claude-sonnet-5"] picks the model.

Other editors

Any ACP client that starts an agent as a command works the same way: the command is friday, its arguments acp and any session flags. The engine needs nothing else: no Node.js, no port, no login. If the TypeScript agent is installed (the npm package installs it), settings and provider methods are answered through it; without it the engine still runs sessions.

What an editor gets

ACP	Friday
`initialize`	protocol version 1, `loadSession: true`, prompts with text and embedded context
`session/new`	a session in the editor's folder, with four modes: `plan`, `build` (current), `auto`, `defender`
`session/load`	an earlier session, with its conversation replayed
`session/prompt`	one turn; text, embedded files (`resource`) and file links (`resource_link`) are understood
`session/update`	the reply as `agent_message_chunk`; each tool call as `tool_call` (with a title such as `edit file: src/app.ts` and a kind: read, edit, search, execute, think) and `tool_call_update` (completed or failed, with the result)
`session/request_permission`	before a call that changes something, with up to five options: allow once, allow from now on, a broader pattern when it is safe, deny, deny from now on
`session/cancel`	stops the turn, and any prompt the editor sent before the cancel
`session/set_mode`	changes what Friday may do; standing approvals are kept

Stop reasons are end_turn, cancelled and max_turn_requests (the turn's step budget ran out).

The extension

An editor (or the Friday interface) can opt in to more with clientCapabilities._meta.archymedes.events: true in initialize. It then also receives _archymedes/event notifications: token usage per model call, retries, sub-agent activity and thread status, compaction, test-first progress, and why a turn stopped. With _meta.archymedes.questions: true, Friday can ask the person questions (_archymedes/session/ask). The Protocol reference lists every method and event.

Troubleshooting

Nothing happens in the editor: run friday acp in a terminal and paste {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":1}}; Friday should answer with one line of JSON. Anything else it prints on standard error is the reason.
"No model provider is configured": run friday settings once in a terminal.
A protocol log: use the editor's own ACP log. (ARCHYMEDES_ACP_TRACE records the protocol only when Friday's own interface is the client.)

Sources for the Zed configuration: Zed's agent settings and the change that added custom agent servers, acp: Support launching custom agent servers (#36805).

Kept in the repository as docs/engine/EDITORS.md, checked by its conformance tests · synced at af2a9b2