version: "1.0.2" name: acpx description: Use acpx as a headless ACP CLI for agent-to-agent communication. Use when running coding agents through acpx, managing persistent ACP sessions, queueing prompts, overriding the Claude system prompt, consuming structured agent output from scripts, or composing multi-agent workflows 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>]

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
• gemini -> gemini --acp
• cursor -> cursor-agent acp
• copilot -> copilot --acp --stdio
• droid -> droid exec --output-format acp
• fast-agent -> uvx fast-agent-mcp acp
• 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
• 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.

Key commands

Prompt (default, persistent session)

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

• Uses a saved session for the session scope key, auto-resumes prior session
• 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>, --no-wait, -f, --file <path>

Exec (one-shot)

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

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

• cancel: sends cooperative session/cancel through queue-owner IPC
• set-mode: calls ACP session/set_mode
• set: calls ACP session/set_config_option
• set model <id>: calls session/set_model for mid-session model switching

Sessions

acpx sessions list                          # list all sessions
acpx sessions new --name backend            # create fresh session
acpx sessions ensure --name backend         # idempotent: get or create
acpx sessions close backend                 # close a session
acpx sessions show backend                  # show metadata
acpx sessions history backend --limit 20    # show turn history
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                                 # check local agent process

Prefix any command with an agent name: acpx codex sessions ensure --name backend

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
• --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
• --system-prompt <text>: replace the agent system prompt (persisted in session)
• --append-system-prompt <text>: append text to the agent 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
• --verbose: verbose ACP/debug logs to stderr

Permission flags are mutually exclusive.

System prompt override (Claude)

# 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 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.

Config files

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

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

Supported keys: defaultAgent, defaultPermissions, nonInteractivePermissions, ttl, timeout, format, agents map, auth map.

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.

Session behavior

Persistent prompt sessions are scoped by: agentCommand, absolute cwd, optional session name.

• 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
• 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

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.

• 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
• After the queue drains, owner shutdown is governed by TTL (default 300s, configurable with --ttl)

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]
• --json-strict: pair with --format json to suppress non-JSON stderr noise

Example automation:

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

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.

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.

The authoring surface lives in acpx/flows. Node types: acp (model-driven step), decision (constrained-choice LLM step), action (runtime-supervised deterministic operation), compute (pure local data transform), checkpoint (pause point for human or external trigger).

See references/advanced.md for the full authoring example, edge shapes, and detailed node type reference.

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'