Subagent Spawn Book Agent Skill

Subagent Spawn Book (SSB). Use before creating any subagent and before choosing which model leads a session or orchestrates a run…

Context cost
6k tokensestimated from the bundle, loaded when it triggers
Bundle
8 files · 23.8 kBtext throughout, nothing executable
Licence
not declarednone named by its author
Last change
—v3.0.0
Servers it uses
Noneruns standalone

What it does

Subagent Spawn Book (SSB). Use before creating any subagent and before choosing which model leads a session or orchestrates a run: whenever the user asks for one, a plan includes delegation or fan-out, or the work at hand would go better in another session, such as research, a browser or computer-use task, a review or critique, a visual check, a bulk job, or anything another model would do better.

What this skill changes about the agent has not been set out here as a list. Its SKILL.md, shown below, says it in the author’s own words.

productivity

The skill itself

A skill is instructions the model reads, so you can see what you are getting: below is the start of its SKILL.md. The front matter loads with every session, the body loads when the skill triggers, and the whole file comes with the install.

SKILL.md9.0 kB · preview
--- name: "subagent-spawn-book" metadata: author: "Leeor Nahum" version: "3.0.0" ---
9# Subagent Spawn Book
10
11Use this skill before creating any subagent. A subagent is any separate model, agent, task runner, chat, CLI invocation, or orchestrator worker asked to handle part of the work, including a session that will run the work itself and delegate further.
12
13This skill is a spawn book. It owns which model to select and how to find the exact spawn instructions. It does not own general prompting technique, task planning, or review method.
14
15## Universal Spawn Rules
16
17- Apply this skill at every spawn point, not once per session. Having read it earlier does not cover a later spawn: an orchestrator that fans out repeatedly, a mind that spawns its own researchers, or a plan step that delegates each re-applies the selection and naming rules to the spawn at hand.
18- If the user names a specific model or agent, use that target unless it is unavailable in its own harness or unsafe for the requested action.
19- Interpret informal model names from context and current provider naming. Do not require an exact reference heading when the user's intent is clear.
20- If the user does not name a target, choose from the model section below without asking the user to pick.
21- Treat this skill as a set of defaults for concise delegation. User, agent, plan, or project instructions override the defaults when they specify an undocumented model, mode, permission profile, harness, fan-out shape, or spawn method. When a project pins a model or a fan-out shape, follow it and say so at the spawn point rather than silently skipping this skill.
22- A critic is spawned on a different provider than the work it checks, and is given the goal and the work rather than the builder's framing, so it does not inherit the builder's assumptions. It is the lowest-priced frontier model of the other provider: GPT Sol when a Claude model built the work, Claude Opus when a GPT model built it. When only one provider is reachable, use that provider's lowest-priced frontier model that did not build the work, never Claude Fable unless the user named it, or else a fresh session of the builder's model, and say in the report that the check was same-provider, because it is weaker.
23- If the current harness is the selected model's own harness, or the current session genuinely serves the selected model, use its internal subagent tooling. Confirm the internal tooling actually spawns the selected model at the effort chosen for the spawn, whether the user named it or the reference sets it. If internal subagents are pinned to a different model, or the tooling cannot reach that effort by any route the model's reference documents, that does not count. Spawn through the native command instead, and say so at the spawn point.
24- If the current harness is not the selected model's own harness, spawn the model through its own harness using the selected reference.
25- If the user, plan, or orchestrator names a spawn preference, apply it after resolving the model. Do not treat access to a model inside another harness as model ownership.
26- Read the selected model's reference before spawning it. References are model-specific and teach the exact spawn command and how to resume the session.
27- A spawned session can be resumed by its id with a reply, and it keeps its context. Use that for a back-and-forth, such as a critic answering the builder's response, instead of starting over.
This is a preview of SKILL.md. Download or install the skill to get the whole thing.
In the file
SKILL.md1,498 words
Files8
Licencenot declared
Why you can read it

Nothing in a skill executes. The client loads the text and the model follows it, so a skill can be audited the way a runbook is — by reading it.

What it costs in context

Skills are not billed by the call. They are paid for in context: every token the instructions occupy is a token your code, your diff and your conversation cannot use. Here is what this one takes and when it takes it.

≈130
always loaded
The name and description, so the model knows the skill exists and when to reach for it.
5,820
on trigger
The instruction body and 7 supporting files, read only when the skill fires.
3.0%
of a 200k window
Ten skills this size would take about 30% of the window before you open a file.
050k100k150k200k context window

6k tokens, estimated from the bundle at four bytes to the token, held for the rest of the session once it triggers. Heavy. Teams tend to install this one per project rather than globally, and load it only when the job comes up.

Servers bill, skills cost

A server charges by the month. A skill charges once per session, in context, and then keeps charging it for as long as the session lives.

Before and after

The same question, put to the same model twice: once as it comes, and once with these instructions loaded.

No worked example has been published for this skill yet.

The procedure it runs

The procedure has not been set out here step by step. It is in the body of its SKILL.md: the start of it is shown above, and the whole file comes with the install.

Prose, not code

These steps are written for a model to follow, not executed by a runtime. It can still be told to skip one, and it will say so when it does.

Servers it uses

None. This skill calls no MCP servers at all.

Everything it needs is in the instructions, so it works in a project with nothing connected — the model reads the file and changes how it works with what it can already reach.

Its SKILL.md does not declare which tools it asks the agent for, so what it touches is whatever the instructions themselves ask for — read them before you install it.

What it asks for
Writes filesnot declared
Network accessnot declared

This SKILL.md carries no allowed-tools line, so neither is declared. A skill grants no permissions of its own — it can only ask for tools your client already has.

What it will not do

Every skill is narrow, and the useful ones say where they stop. These are the jobs this one is the wrong tool for.

What this skill is not for has not been published here. Nothing is implied by that: it is a section the author has not filled in.

What is in the bundle

8 files, 23.8 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

  • SKILL.md9.0 kB
  • AGENTS.md4.3 kB
  • README.md0.4 kB
  • references/claude-fable.md2.0 kB
  • references/claude-opus.md2.6 kB
  • references/gpt-astra.md1.8 kB
  • references/gpt-luna.md1.4 kB
  • references/gpt-sol.md2.3 kB
What is not in it

No dependencies and nothing executable: a skill is text the agent reads, so the bundle is 8 files you can review in full before installing.

Install

Installing copies the bundle into your project. Nothing runs at install time — the files sit on disk until the model reads them.

# Subagent Spawn Book · 6k tokens when loaded · macOS, Linux mkdir -p .claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/subagent-spawn-book/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/subagent-spawn-book" ] && { [ ! -e .claude/skills/subagent-spawn-book ] || { mv .claude/skills/subagent-spawn-book "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/subagent-spawn-book" .claude/skills/ && echo "Installed .claude/skills/subagent-spawn-book"
On Windows, or any OS with Node 20+
npx mcprush@latest skill add leeornahum/subagent-spawn-book

Windows PowerShell says 'running scripts is disabled on this system'? Run Set-ExecutionPolicy -Scope CurrentUser RemoteSigned once, or type npx.cmd instead of npx (codex.cmd, gemini.cmd, grok.cmd likewise). PowerShell 7 needs neither. Writes to .claude/skills/subagent-spawn-book/ in the current project. For every project instead, run mkdir -p ~/.claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/subagent-spawn-book/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/subagent-spawn-book" ] && { [ ! -e ~/.claude/skills/subagent-spawn-book ] || { mv ~/.claude/skills/subagent-spawn-book "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/subagent-spawn-book" ~/.claude/skills/ && echo "Installed ~/.claude/skills/subagent-spawn-book" (macOS, Linux) — or add --global to the npx line. The curl line replaces .claude/skills/subagent-spawn-book/ only after the download succeeds, so files left there by another skill of the same name, or by an older release, do not mix in. A copy already there is moved aside, not deleted, and the line prints where.

Which clients pick it up on their own

A skill is a folder of text. Most of these read a skills folder and pick it up without being told; the rest take the same folder another way — an upload in the app, a parameter on an API call — and then choose it by its description just the same.

Claude Code.claude/skills/
Claude DesktopCustomize › Skills
ChatGPTSkills › Create › Upload
Cursor.cursor/skills/
VS Code.github/skills/
Codex CLI.agents/skills/
Gemini CLI.gemini/skills/
Grok Build.grok/skills/
Microsoft CopilotSkills › Upload a skill
PerplexityComputer › Skills › Upload a skill
DeepSeek Harness.dsh/skills/
Zed.agents/skills/
Devin Desktop.devin/skills/
Windsurf (legacy).windsurf/skills/
OpenAI Agents SDKInstructions or sandbox Skills
HTTP / APIa request parameter
This release
Version3.0.0
Publishedno release date on file
PriceFree
Referenceleeornahum/subagent-spawn-book

Versions

v3.0.0 is what is on the shelf; no release here carries a date. Instructions change more often than APIs do — a skill can be rewritten entirely without anything it depends on moving.

v3.0.0
  • No earlier releases have been published to the marketplace.
Pinning

The install command always fetches the release that is current the day you run it — v3.0.0 today — and cannot ask for an earlier one. The copy on your disk does not change until you run it again.

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