subagent - SKILL.md Agent Skill

name: subagent description: Spawn and manage autonomous background agents for parallel work compatibility: "Designed for Vellum personal assistants" metadata: emoji: "🤖" vellum: display-name: "Subagent" category: "system" activation-hints: - "Spawn a background worker that runs in parallel with the main turn" - "Delegate a self-contained research or implementation task off the main thread" - "Multiple agents at once, or a context-inheriting fork" avoid-when: - "Task is small enough to do inline (single tool call, quick lookup)" - "User wants Claude Code or Codex — use the acp skill instead"

Subagent orchestration -- spawn background agents to work on tasks in parallel.

Lifecycle

Subagents follow this status flow: pending -> running -> completed / failed / aborted

Spawn: Use subagent_spawn with a label, objective, and role. The subagent runs autonomously.
Mid-run communication: Subagents can send notifications to the parent via notify_parent while still running -- useful for sharing interim findings or signaling that they are blocked.
Auto-notification: The parent conversation is automatically notified when a subagent reaches a terminal status (completed/failed/aborted). Do NOT poll subagent_status.
Read output: Use subagent_read after the subagent reaches a terminal status to retrieve its full output.

Roles

Each subagent is spawned with a role that determines its tool access. Choose the most restrictive role that can accomplish the task.

recall is local information search across memory, the personal knowledge base, past conversations, and workspace files. Use it when a subagent needs prior context that is not already in the prompt.

Role	Tools	When to use
`general`	Full tool access	Task genuinely needs unrestricted capabilities (rare -- prefer a specialized role)
`researcher`	`web_search`, `web_fetch`, `file_read`, `file_list`, `recall`, `notify_parent`	Information gathering, web research, codebase exploration, reading documentation
`coder`	`bash`, `file_read`, `file_write`, `file_edit`, `web_search`, `recall`, `notify_parent`	Code changes, file editing, running commands, build/test tasks
`planner`	`file_read`, `file_list`, `web_search`, `web_fetch`, `recall`, `notify_parent`	Analysis, planning, synthesizing information, reviewing approaches
`investigator`	`bash`, `file_read`, `file_list`, `web_search`, `web_fetch`, `recall`, `notify_parent`	Root-cause analysis: debugging, log forensics, tracing behavior across many files. Shell access is for read-only investigation (grep/find/reading logs); returns a compact root-cause report

All specialized roles (researcher, coder, planner) include notify_parent for mid-run communication with the parent.

Parent Communication

Subagents use notify_parent to send messages to the parent conversation while still running. Each notification has an urgency level:

info -- Progress updates, minor findings. The parent is informed but does not need to act.
important -- Key findings, significant results. The parent should review when convenient.
blocked -- The subagent needs guidance or a decision from the parent to continue.

Use notifications judiciously -- one per major finding or milestone. Do not send a notification for every small step.

Naming

Subagents can be referenced by label instead of UUID. The label parameter is accepted on subagent_message, subagent_status, subagent_read, and subagent_abort as an alternative to subagent_id. Label lookup is case-insensitive.

Use descriptive labels when spawning subagents (e.g., "research-auth-libraries", "implement-login-form") so they are easy to reference later.

Reading Output

subagent_read returns the subagent's assistant text output. Use the last_n parameter to retrieve only the most recent N assistant messages instead of the full history. This is useful for large outputs where you only need the final result.

Ownership

Only the parent conversation that spawned a subagent can interact with it (check status, send messages, abort, or read output).

Silent Mode

Set send_result_to_user: false when spawning a subagent whose result is for internal processing only. The parent will still be notified on completion, but the notification will instruct it to read the result without presenting it to the user.

Fork Mode

Forks are sub-agents that inherit the parent's full context -- messages, system prompt, and memory -- sharing the KV cache for near-free context inheritance. Use forks when the task benefits from knowing what you've been discussing; use a regular sub-agent when the task is self-contained.

Key behaviors: Forks always run as general role (the role parameter is ignored). send_result_to_user defaults to false. Read fork output with last_n: 1 to get only the final synthesis.

When to fork vs regular sub-agent:

Task	Mode
Single tool call (one search, one file read)	Direct -- don't spawn at all
Multi-page web research needing conversation context	Fork
Exploratory file search informed by prior discussion	Fork
Comparing multiple sources against what was discussed	Parallel forks
Self-contained task with a clear objective	Regular sub-agent

Rule of thumb: "Does this task need to know what we've been talking about?" If yes, fork. If the objective is fully self-describing, use a regular sub-agent with a scoped role.

Tips

Do NOT poll subagent_status in a loop. You will be notified automatically when a subagent completes.
Use roles to scope tool access and minimize blast radius. Default to the most restrictive role that works.
Spawn a researcher and coder in parallel for research-then-implement workflows -- the researcher gathers context while the coder starts on the known parts.
Use notify_parent for interim findings instead of waiting for completion. This lets the parent act on partial results early.
Use subagent_message to send follow-up instructions to a running subagent.
Use subagent_abort to cancel a subagent that is no longer needed.
Default to spawning subagents for any task that involves web research, multi-file exploration, or independent coding work. Serial execution should be the exception, not the rule.
Delegate root-cause investigations ("why is X happening?", debugging, log forensics) to an investigator instead of grepping inline. A long investigation done inline floods your own context with file slices and grep output, crowding out the conversation; the investigator does the digging in its own context and returns a compact root-cause report.
When a user request has both an information-gathering component and an action component, spawn a researcher immediately rather than doing the research inline yourself.
Prefer spawning 2-3 focused subagents over one large general-purpose subagent. Smaller scopes finish faster and fail more gracefully.