docs/tools/subagents.md

metadata

summary: >-
  Sub-agents: spawning isolated agent runs that announce results back to the
  requester chat
read_when:
  - You want background/parallel work via the agent
  - You are changing sessions_spawn or sub-agent tool policy
title: Sub-Agents

Sub-agents

Sub-agents are background agent runs spawned from an existing agent run. They run in their own session (agent:<agentId>:subagent:<uuid>) and, when finished, announce their result back to the requester chat channel.

Slash command

Use /subagents to inspect or control sub-agent runs for the current session:

• /subagents list
• /subagents kill <id|#|all>
• /subagents log <id|#> [limit] [tools]
• /subagents info <id|#>
• /subagents send <id|#> <message>

/subagents info shows run metadata (status, timestamps, session id, transcript path, cleanup).

Primary goals:

• Parallelize "research / long task / slow tool" work without blocking the main run.
• Keep sub-agents isolated by default (session separation + optional sandboxing).
• Keep the tool surface hard to misuse: sub-agents do not get session tools by default.
• Support configurable nesting depth for orchestrator patterns.

Cost note: each sub-agent has its own context and token usage. For heavy or repetitive tasks, set a cheaper model for sub-agents and keep your main agent on a higher-quality model. You can configure this via agents.defaults.subagents.model or per-agent overrides.

Tool

Use sessions_spawn:

• Starts a sub-agent run (deliver: false, global lane: subagent)
• Then runs an announce step and posts the announce reply to the requester chat channel
• Default model: inherits the caller unless you set agents.defaults.subagents.model (or per-agent agents.list[].subagents.model); an explicit sessions_spawn.model still wins.
• Default thinking: inherits the caller unless you set agents.defaults.subagents.thinking (or per-agent agents.list[].subagents.thinking); an explicit sessions_spawn.thinking still wins.

Tool params:

• task (required)
• label? (optional)
• agentId? (optional; spawn under another agent id if allowed)
• model? (optional; overrides the sub-agent model; invalid values are skipped and the sub-agent runs on the default model with a warning in the tool result)
• thinking? (optional; overrides thinking level for the sub-agent run)
• runTimeoutSeconds? (default 0; when set, the sub-agent run is aborted after N seconds)
• cleanup? (delete|keep, default keep)

Allowlist:

• agents.list[].subagents.allowAgents: list of agent ids that can be targeted via agentId (["*"] to allow any). Default: only the requester agent.

Discovery:

• Use agents_list to see which agent ids are currently allowed for sessions_spawn.

Auto-archive:

• Sub-agent sessions are automatically archived after agents.defaults.subagents.archiveAfterMinutes (default: 60).
• Archive uses sessions.delete and renames the transcript to *.deleted.<timestamp> (same folder).
• cleanup: "delete" archives immediately after announce (still keeps the transcript via rename).
• Auto-archive is best-effort; pending timers are lost if the gateway restarts.
• runTimeoutSeconds does not auto-archive; it only stops the run. The session remains until auto-archive.
• Auto-archive applies equally to depth-1 and depth-2 sessions.

Nested Sub-Agents

By default, sub-agents cannot spawn their own sub-agents (maxSpawnDepth: 1). You can enable one level of nesting by setting maxSpawnDepth: 2, which allows the orchestrator pattern: main → orchestrator sub-agent → worker sub-sub-agents.

How to enable

{
  agents: {
    defaults: {
      subagents: {
        maxSpawnDepth: 2, // allow sub-agents to spawn children (default: 1)
        maxChildrenPerAgent: 5, // max active children per agent session (default: 5)
        maxConcurrent: 8, // global concurrency lane cap (default: 8)
      },
    },
  },
}

Depth levels

Depth	Session key shape	Role	Can spawn?
0	agent:<id>:main	Main agent	Always
1	agent:<id>:subagent:<uuid>	Sub-agent (orchestrator when depth 2 allowed)	Only if maxSpawnDepth >= 2
2	agent:<id>:subagent:<uuid>:subagent:<uuid>	Sub-sub-agent (leaf worker)	Never

Announce chain

Results flow back up the chain:

1. Depth-2 worker finishes → announces to its parent (depth-1 orchestrator)
2. Depth-1 orchestrator receives the announce, synthesizes results, finishes → announces to main
3. Main agent receives the announce and delivers to the user

Each level only sees announces from its direct children.

Tool policy by depth

• Depth 1 (orchestrator, when maxSpawnDepth >= 2): Gets sessions_spawn, subagents, sessions_list, sessions_history so it can manage its children. Other session/system tools remain denied.
• Depth 1 (leaf, when maxSpawnDepth == 1): No session tools (current default behavior).
• Depth 2 (leaf worker): No session tools — sessions_spawn is always denied at depth 2. Cannot spawn further children.

Per-agent spawn limit

Each agent session (at any depth) can have at most maxChildrenPerAgent (default: 5) active children at a time. This prevents runaway fan-out from a single orchestrator.

Cascade stop

Stopping a depth-1 orchestrator automatically stops all its depth-2 children:

• /stop in the main chat stops all depth-1 agents and cascades to their depth-2 children.
• /subagents kill <id> stops a specific sub-agent and cascades to its children.
• /subagents kill all stops all sub-agents for the requester and cascades.

Authentication

Sub-agent auth is resolved by agent id, not by session type:

• The sub-agent session key is agent:<agentId>:subagent:<uuid>.
• The auth store is loaded from that agent's agentDir.
• The main agent's auth profiles are merged in as a fallback; agent profiles override main profiles on conflicts.

Note: the merge is additive, so main profiles are always available as fallbacks. Fully isolated auth per agent is not supported yet.

Announce

Sub-agents report back via an announce step:

• The announce step runs inside the sub-agent session (not the requester session).
• If the sub-agent replies exactly ANNOUNCE_SKIP, nothing is posted.
• Otherwise the announce reply is posted to the requester chat channel via a follow-up agent call (deliver=true).
• Announce replies preserve thread/topic routing when available (Slack threads, Telegram topics, Matrix threads).
• Announce messages are normalized to a stable template:
  • Status: derived from the run outcome (success, error, timeout, or unknown).
  • Result: the summary content from the announce step (or (not available) if missing).
  • Notes: error details and other useful context.
• Status is not inferred from model output; it comes from runtime outcome signals.

Announce payloads include a stats line at the end (even when wrapped):

• Runtime (e.g., runtime 5m12s)
• Token usage (input/output/total)
• Estimated cost when model pricing is configured (models.providers.*.models[].cost)
• sessionKey, sessionId, and transcript path (so the main agent can fetch history via sessions_history or inspect the file on disk)

Tool Policy (sub-agent tools)

By default, sub-agents get all tools except session tools and system tools:

• sessions_list
• sessions_history
• sessions_send
• sessions_spawn

When maxSpawnDepth >= 2, depth-1 orchestrator sub-agents additionally receive sessions_spawn, subagents, sessions_list, and sessions_history so they can manage their children.

Override via config:

{
  agents: {
    defaults: {
      subagents: {
        maxConcurrent: 1,
      },
    },
  },
  tools: {
    subagents: {
      tools: {
        // deny wins
        deny: ["gateway", "cron"],
        // if allow is set, it becomes allow-only (deny still wins)
        // allow: ["read", "exec", "process"]
      },
    },
  },
}

Concurrency

Sub-agents use a dedicated in-process queue lane:

• Lane name: subagent
• Concurrency: agents.defaults.subagents.maxConcurrent (default 8)

Stopping

• Sending /stop in the requester chat aborts the requester session and stops any active sub-agent runs spawned from it, cascading to nested children.
• /subagents kill <id> stops a specific sub-agent and cascades to its children.

Limitations

• Sub-agent announce is best-effort. If the gateway restarts, pending "announce back" work is lost.
• Sub-agents still share the same gateway process resources; treat maxConcurrent as a safety valve.
• sessions_spawn is always non-blocking: it returns { status: "accepted", runId, childSessionKey } immediately.
• Sub-agent context only injects AGENTS.md + TOOLS.md (no SOUL.md, IDENTITY.md, USER.md, HEARTBEAT.md, or BOOTSTRAP.md).
• Maximum nesting depth is 5 (maxSpawnDepth range: 1–5). Depth 2 is recommended for most use cases.
• maxChildrenPerAgent caps active children per session (default: 5, range: 1–20).