acpx

name	acpx
description	Use acpx as a headless ACP CLI for agent-to-agent communication, including prompt/exec/sessions workflows, session scoping, queueing, permissions, output formats, system-prompt overrides, and multi-agent flows authored with defineFlow/decision/decisionEdge.

acpx

When to use this skill

Use this skill when you need to run coding agents through acpx, manage persistent ACP sessions, queue prompts, override the Claude system prompt, prune stale sessions, consume structured agent output from scripts, or compose multi-agent workflows declaratively with acpx/flows.

What acpx is

acpx is a headless, scriptable CLI client for the Agent Client Protocol (ACP). It is built for agent-to-agent communication over the command line and avoids PTY scraping.

Core capabilities:

• Persistent multi-turn sessions per repo/cwd
• One-shot execution mode (exec)
• Named parallel sessions (-s/--session)
• Idempotent session creation (sessions ensure)
• Session retention controls (sessions prune with age filters and history cleanup)
• Portable session export/import for moving records and history across machines
• Queue-aware prompt submission with optional fire-and-forget (--no-wait)
• Cooperative cancel command (cancel) for in-flight turns
• Graceful cancellation via ACP session/cancel on interrupt
• Session control methods (set-mode, set <key> <value>)
• Agent reconnect/resume after dead subprocess detection
• Prompt input via stdin or --file
• Config files with global+project merge and config show|init
• Session metadata/history inspection (sessions show, sessions history)
• Local agent process checks via status
• Stable ACP client methods for filesystem and terminal requests
• Stable ACP authenticate handshake via env/config credentials
• Structured streaming output (text, json, quiet) with optional --suppress-reads
• Built-in agent registry plus raw --agent escape hatch
• Claude system prompt override via --system-prompt / --append-system-prompt
• Optional terminal capability disable via --no-terminal for review-only flows
• Tool whitelist (--allowed-tools), turn cap (--max-turns), retry on transient failures (--prompt-retries)
• Multi-agent flows via acpx flow run and the acpx/flows authoring API (defineFlow, decision, decisionEdge, acp, action, compute, checkpoint)

Install

npm i -g acpx

For normal session reuse, prefer a global install over npx.

Command model

prompt is the default verb.

acpx [global_options] [prompt_text...]
acpx [global_options] prompt [prompt_options] [prompt_text...]
acpx [global_options] exec [prompt_options] [prompt_text...]
acpx [global_options] cancel [-s <name>]
acpx [global_options] set-mode <mode> [-s <name>]
acpx [global_options] set <key> <value> [-s <name>]
acpx [global_options] status [-s <name>]
acpx [global_options] sessions [list | new [--name <name>] | ensure [--name <name>] | close [name] | show [name] | history [name] [--limit <count>] | export [name] --output <path> | import <archive> [--name <name>] [--cwd <dir>] | prune [--dry-run] [--before <date> | --older-than <days>] [--include-history]]
acpx [global_options] config [show | init]
acpx [global_options] flow run <file> [--input-json '<json>' | --input-file <path>] [--default-agent <name>]

acpx [global_options] <agent> [prompt_options] [prompt_text...]
acpx [global_options] <agent> prompt [prompt_options] [prompt_text...]
acpx [global_options] <agent> exec [prompt_options] [prompt_text...]
acpx [global_options] <agent> cancel [-s <name>]
acpx [global_options] <agent> set-mode <mode> [-s <name>]
acpx [global_options] <agent> set <key> <value> [-s <name>]
acpx [global_options] <agent> status [-s <name>]
acpx [global_options] <agent> sessions [list | new [--name <name>] | ensure [--name <name>] | close [name] | show [name] | history [name] [--limit <count>] | export [name] --output <path> | import <archive> [--name <name>] [--cwd <dir>] | prune [--dry-run] [--before <date> | --older-than <days>] [--include-history]]

If prompt text is omitted and stdin is piped, acpx reads prompt text from stdin.

Built-in agent registry

Friendly agent names resolve to commands:

• pi -> npx pi-acp
• openclaw -> openclaw acp
• codex -> npx -y @agentclientprotocol/codex-acp
• claude -> npx -y @agentclientprotocol/claude-agent-acp (ACPX-owned package range)
• gemini -> gemini --acp
• cursor -> cursor-agent acp
• copilot -> copilot --acp --stdio
• droid -> droid exec --output-format acp (factory-droid and factorydroid also resolve to droid)
• iflow -> iflow --experimental-acp
• kilocode -> npx -y @kilocode/cli acp
• kimi -> kimi acp
• kiro -> kiro-cli-chat acp
• opencode -> npx -y opencode-ai acp
• qoder -> qodercli --acp Forwards Qoder-native --allowed-tools and --max-turns startup flags from acpx session options.
• qwen -> qwen --acp
• trae -> traecli acp serve

Rules:

• Default agent is codex for top-level prompt, exec, and sessions.
• Unknown positional agent tokens are treated as raw agent commands.
• --agent <command> explicitly sets a raw ACP adapter command.
• Do not combine a positional agent and --agent in the same command.

Commands

Prompt (default, persistent session)

Implicit:

acpx codex 'fix flaky tests'

Explicit:

acpx codex prompt 'fix flaky tests'
acpx prompt 'fix flaky tests'   # defaults to codex

Behavior:

• Uses a saved session for the session scope key
• Auto-resumes prior session when one exists for that scope
• If no session exists for the scope, exits with NO_SESSION and prompts for sessions new
• Is queue-aware when another prompt is already running for the same session
• On interrupt during an active turn, sends ACP session/cancel before force-kill fallback

Prompt options:

• -s, --session <name>: use a named session within the same cwd
• --no-wait: enqueue and return immediately when session is already busy
• -f, --file <path>: read prompt text from file (- means stdin)

Exec (one-shot)

acpx exec 'summarize this repo'
acpx codex exec 'summarize this repo'

Behavior:

• Runs a single prompt in a temporary ACP session
• Does not reuse or save persistent session state

Cancel / Mode / Config / Model

acpx codex cancel
acpx codex set-mode auto
acpx codex set model gpt-5.2[high]
acpx codex set model gpt-5.4

Behavior:

• cancel: sends cooperative session/cancel through queue-owner IPC.
• set-mode: calls ACP session/set_mode.
• set-mode mode ids are adapter-defined; unsupported values are rejected by the adapter (often Invalid params).
• set: calls ACP session/set_config_option.
• For codex, reasoning effort is selected through advertised ACP model ids when the adapter reports model variants.
• --model <id>: Claude-compatible adapters may consume session creation metadata; other agents must advertise ACP models and support session/set_model, otherwise acpx fails clearly instead of silently falling back.
• set model <id>: calls session/set_model. This is the generic ACP method for mid-session model switching.
• set-mode/set route through queue-owner IPC when active, otherwise reconnect directly.

Sessions

acpx sessions
acpx sessions list
acpx sessions list --filter-cwd .
acpx sessions list --cursor <cursor>
acpx sessions list --local
acpx sessions new
acpx sessions new --name backend
acpx sessions ensure
acpx sessions ensure --name backend
acpx sessions close
acpx sessions close backend
acpx sessions show
acpx sessions history --limit 20
acpx sessions export backend --output backend-session.json
acpx sessions import backend-session.json --name backend-restored
acpx sessions prune --dry-run --older-than 7
acpx sessions prune --older-than 30 --include-history
acpx status

acpx codex sessions
acpx codex sessions new --name backend
acpx codex sessions ensure --name backend
acpx codex sessions close backend
acpx codex sessions show backend
acpx codex sessions history backend --limit 20
acpx codex sessions export backend --output backend-session.json
acpx codex sessions import backend-session.json --name backend-restored
acpx codex sessions prune --before 2026-04-01 --include-history
acpx codex status

Behavior:

• sessions and sessions list are equivalent
• sessions list uses ACP session/list when the agent advertises it; JSON includes agent SessionInfo, _meta, and nextCursor
• sessions list --filter-cwd <dir> applies the ACP cwd filter, and --cursor <cursor> requests a specific page
• sessions list --local reads saved acpx records instead
• new creates a fresh session for the current (agentCommand, cwd, optional name) scope
• new --name <name> targets a named session scope
• when new replaces an existing open session in that scope, the old one is soft-closed
• ensure returns the nearest matching active session for the scope, or creates one when none is open. Idempotent — safe to call before every prompt in scripts.
• close targets current cwd default session
• close <name> targets current cwd named session
• show [name] prints stored metadata for that scoped session
• history [name] prints stored turn history previews (default 20, use --limit)
• export [name] --output <path> writes a portable JSON archive containing session state and event history
• import <archive> creates a fresh local record, reopens the copied session as idle, keeps the provider session id, and clears source-machine process metadata
• imported sessions must resume that provider session; if the destination agent cannot load it, prompts fail clearly instead of starting an empty conversation
• import --name <name> and --cwd <dir> override the destination scope; import fails if that scope already has an active session or another local record already uses the same provider session id
• prune deletes closed session records to reclaim disk space
  • --dry-run previews what would be deleted without touching disk
  • --older-than <days> and --before <date> filter by close time, falling back to last-used time when a record was never explicitly closed
  • --include-history also removes per-session event stream files (otherwise only the JSON record is removed)

Global options

• --agent <command>: raw ACP agent command (escape hatch)
• --cwd <dir>: working directory for session scope (default: current directory)
• --approve-all: auto-approve all permission requests
• --approve-reads: auto-approve reads/searches, prompt for writes (default mode)
• --deny-all: deny all permission requests
• --non-interactive-permissions <policy>: when prompting is unavailable, choose deny or fail
• --permission-policy <json-or-file> / --policy: per-tool ACP permission rules (autoApprove, autoDeny, escalate, defaultAction)
• --format <fmt>: output format (text, json, quiet)
• --json-strict: strict JSON mode; requires --format json and suppresses non-JSON stderr output
• --suppress-reads: suppress raw read-file contents while preserving the selected format
• --timeout <seconds>: max wait time (positive number)
• --ttl <seconds>: queue owner idle TTL before shutdown (default 300, 0 disables TTL)
• --model <id>: request an agent model during session creation; non-Claude agents must advertise ACP models and support session/set_model
• --system-prompt <text>: replace the agent system prompt. Forwarded to claude-agent-acp via ACP _meta.systemPrompt; persisted in session_options.system_prompt so reuse keeps the override. Other agents ignore the field.
• --append-system-prompt <text>: append text to the agent system prompt. Forwarded to claude-agent-acp via ACP _meta.systemPrompt.append; same persistence rules as --system-prompt.
• --allowed-tools <list>: comma-separated tool whitelist (use "" for no tools)
• --max-turns <count>: cap session turn count
• --prompt-retries <count>: retry failed prompt turns on transient errors (default 0)
• --no-terminal: do not advertise the ACP terminal capability — useful for review-only or sandboxed agent invocations
• --verbose: verbose ACP/debug logs to stderr

Permission flags are mutually exclusive.

System prompt override (Claude)

--system-prompt and --append-system-prompt let you specialize a Claude session without leaving lingering one-off state, while still benefiting from persistent session reuse.

# Replace the system prompt for a named session, persisted across reuse
acpx --system-prompt "You are a code reviewer who challenges every implicit assumption." claude -s review

# Append a guideline on top of the default system prompt
acpx --append-system-prompt "Always explain trade-offs before recommending a fix." claude -s impl

The override is forwarded via ACP _meta.systemPrompt (or _meta.systemPrompt.append) on session/new and stored in session_options.system_prompt. Subsequent prompt/ensure calls in the same scope keep the override unless you explicitly create a new session. Non-Claude adapters ignore the field, so the same flag is safe inside cross-agent scripts.

Sessions cleanup

Closed session records accumulate on disk by default. Use sessions prune to enforce retention:

# Preview what would be deleted (no writes)
acpx codex sessions prune --dry-run --older-than 7

# Remove records closed more than 30 days ago, including their event-stream files
acpx codex sessions prune --older-than 30 --include-history

# Remove everything closed before a date
acpx codex sessions prune --before 2026-04-01

Without --include-history, only the lightweight JSON record is removed; event-stream files are preserved for audit. With it, the per-session event log is also deleted to reclaim disk space.

Config files

Config files are merged in this order (later wins):

• global: ~/.acpx/config.json
• project: <cwd>/.acpxrc.json

Supported keys:

• defaultAgent
• defaultPermissions (approve-all, approve-reads, deny-all)
• nonInteractivePermissions (deny, fail)
• ttl (seconds)
• timeout (seconds or null)
• format (text, json, quiet)
• agents map (name -> { command, args? })
• auth map (authMethodId -> credential)

Use acpx config show to inspect the resolved config and acpx config init to create the global template.

For ACP authenticate handshakes, use either config auth entries or explicit ACPX_AUTH_<METHOD_ID> environment variables such as ACPX_AUTH_OPENAI_API_KEY. Ambient provider env vars such as OPENAI_API_KEY are still passed through to child agents, but they do not trigger ACP auth-method selection on their own.

Session behavior

Persistent prompt sessions are scoped by:

• agentCommand
• absolute cwd
• optional session name

Persistence:

• Session records are stored in ~/.acpx/sessions/*.json.
• -s/--session creates parallel named conversations in the same repo.
• Changing --cwd changes scope and therefore session lookup.
• closed sessions are retained on disk with closed: true and closedAt until pruned.
• auto-resume by scope skips closed sessions.

Resume behavior:

• Prompt mode attempts to reconnect to saved session.
• If adapter-side session is invalid/not found, acpx creates a fresh session and updates the saved record.
• explicitly selected session records can still be resumed via loadSession even if previously closed.
• dead saved PIDs are detected and reconnected on the next prompt.
• each completed prompt stores lightweight turn history previews in the session record.

Prompt queueing and --no-wait

Queueing is per persistent session.

• The active acpx process for a running prompt becomes the queue owner.
• Other invocations submit prompts over local IPC.
• On Unix-like systems, queue IPC uses a Unix socket under ~/.acpx/queues/<hash>.sock.
• Ownership is coordinated with a lock file under ~/.acpx/queues/<hash>.lock.
• On Windows, named pipes are used instead of Unix sockets.
• after the queue drains, owner shutdown is governed by TTL (default 300s, configurable with --ttl).

Submission behavior:

• Default: enqueue and wait for queued prompt completion, streaming updates back.
• --no-wait: enqueue and return after queue acknowledgement.
• Ctrl+C during an active turn sends ACP session/cancel, waits briefly, then force-kills only if cancellation does not finish in time.
• cancel sends the same cooperative cancellation without requiring terminal signals.

Output formats

Use --format <fmt>:

• text (default): human-readable stream with updates/tool status and done line
• json: NDJSON event stream (good for automation)
• quiet: final assistant text only
• --suppress-reads: replace raw read-file contents with [read output suppressed] in text and json output
• --json-strict: pair with --format json to suppress non-JSON stderr noise (logs, banners) for downstream consumers

Example automation:

acpx --format json codex exec 'review changed files' \
  | jq -r 'select(.type=="tool_call") | [.status, .title] | @tsv'

Permission modes

• --approve-all: no interactive permission prompts
• --approve-reads (default): approve reads/searches, prompt for writes
• --deny-all: deny all permission requests
• --non-interactive-permissions <deny|fail>: chosen behavior when no TTY is available to prompt
• --policy <json-or-file>: match ACP permission requests by tool kind/title; non-interactive escalations add ACP response metadata

If every permission request is denied/cancelled and none approved, acpx exits with permission-denied status.

Flows (multi-agent workflows)

Flows let you declare a multi-agent workflow as a graph of typed nodes connected by edges, executed by the acpx runtime. The runtime owns persistence, retries, timeouts, and routing — the flow file declares the shape, not the engine.

Run a flow

acpx flow run ./my-flow.flow.ts --input-file ./flow-input.json
acpx flow run ./my-flow.flow.ts --input-json '{"task":"FIX: add a regression test"}'
acpx --approve-all flow run examples/flows/pr-triage/pr-triage.flow.ts \
  --input-json '{"repo":"openclaw/acpx","prNumber":150}'
acpx flow run ./my-flow.flow.ts --default-agent claude

Run artifacts persist under ~/.acpx/flows/runs/<runId>/. Default per-step timeout is 15 minutes when --timeout is unset; flows that declare permission requirements fail fast before starting.

Authoring a flow

The authoring surface lives in acpx/flows. The minimal example:

import { acp, decision, decisionEdge, defineFlow, checkpoint, extractJsonObject } from "acpx/flows";

const choices = ["bug", "feat", "doc"] as const;

export default defineFlow({
  name: "pr-triage",
  startAt: "classify",
  nodes: {
    classify: decision({
      choices,
      question: ({ input }) =>
        `Classify the PR description below. Reply with one of: ${choices.join(", ")}.\n\n${input.description}`,
    }),
    bug_lane: acp({
      prompt: ({ outputs }) =>
        `The PR is a bug. Write a regression test that reproduces it.\n\nDecision context: ${JSON.stringify(outputs.classify)}`,
      parse: (text) => extractJsonObject(text),
    }),
    feat_lane: acp({
      prompt: () => "List acceptance criteria for the feature, one bullet per criterion.",
    }),
    doc_lane: checkpoint({
      summary: "doc change — needs human review",
      run: ({ outputs }) => ({ route: "doc", note: outputs.classify }),
    }),
  },
  edges: [
    decisionEdge({
      from: "classify",
      choices,
      cases: {
        bug: "bug_lane",
        feat: "feat_lane",
        doc: "doc_lane",
      },
    }),
  ],
});

Node types

Type	Purpose
acp({ prompt, parse?, agent?, cwd? })	Model-driven step. The prompt builder receives { input, outputs }. Optional parse coerces the raw text (e.g., extractJsonObject).
decision({ choices, question })	Constrained-choice LLM step. choices is a readonly tuple; the runtime validates the model's reply against it and TypeScript infers the union from choices.
action(...)	Runtime-supervised deterministic operation: shell, GitHub API, test execution, comment posting.
compute(...)	Pure local data transform: normalization, routing key derivation, signal reduction.
checkpoint({ summary, run })	Pause point for human or external trigger. run returns the outcome to record while paused.

Edge shapes

// Linear edge
{ from: "node", to: "next" }

// JSONPath switch — non-decision routing
{
  from: "node",
  switch: {
    on: "$.route",
    cases: { "value-a": "branch_a", "value-b": "branch_b" },
  },
}

// Decision edge — exhaustive at compile time
decisionEdge({
  from: "classify",
  choices,                                 // same readonly tuple as decision()
  cases: {                                 // every choice must map to a node id
    bug: "bug_lane",
    feat: "feat_lane",
    doc: "doc_lane",
  },
})

If a decisionEdge omits a case from choices, the TypeScript compiler refuses to compile — so a flow can't ship with a forgotten branch when new choices are added.

Why use flows

• Cross-vendor by construction: classify with codex, write code with claude, summarize with gemini — same flow file, no glue.
• Persistence and replay: every run streams events to disk, replayable via the flow viewer under ~/.acpx/flows/runs/.
• Permission preflight: flows declaring permission requirements fail before any agent starts, instead of mid-run.
• Typed routing: the LLM is constrained to a literal union, the compiler verifies exhaustivity, the runtime validates the reply.

See examples/flows/ in the repo for working samples (branch.flow.ts, pr-triage/, two-turn.flow.ts, shell.flow.ts, workdir.flow.ts).

Practical workflows

Persistent repo assistant:

acpx codex 'inspect failing tests and propose a fix plan'
acpx codex 'apply the smallest safe fix and run tests'

Parallel named streams:

acpx codex -s backend 'fix API pagination bug'
acpx codex -s docs 'draft changelog entry for release'

Specialized Claude reviewer that survives session reuse:

acpx --system-prompt "You are a reviewer who refuses to approve untested changes." claude -s reviewer
acpx claude -s reviewer 'review the diff in src/auth/'

Idempotent session bootstrap (safe to call before every prompt in scripts):

acpx codex sessions ensure -s ci
acpx codex -s ci 'run the smoke suite and report failures'

Queue follow-up without waiting:

acpx codex 'run full test suite and investigate failures'
acpx codex --no-wait 'after tests, summarize root causes and next steps'

One-shot script step:

acpx --format quiet exec 'summarize repo purpose in 3 lines'

Machine-readable output for orchestration:

acpx --format json --json-strict codex 'review current branch changes' > events.ndjson

Raw custom adapter command:

acpx --agent './bin/custom-acp-server --profile ci' 'run validation checks'

Periodic cleanup:

acpx codex sessions prune --dry-run --older-than 14
acpx codex sessions prune --older-than 30 --include-history

Multi-agent triage flow:

acpx --approve-all flow run ./pr-triage.flow.ts --input-json '{"prNumber": 842}'

Repo-scoped review with permissive mode:

acpx --cwd ~/repos/shop --approve-all codex -s pr-842 \
  'review PR #842 for regressions and propose minimal patch'