Fable Sonnet
Run fable-mode execution discipline on Claude Sonnet. Routes the task to the @fable-worker-sonnet agent, whose definition carries the staged loop with step-3 verification enforced hardest (Sonnet's known gap), optionally followed by a cold @fable-verifier pass.
Install
Copy install prompt for AI
Natural-language prompt you can paste into any Claude conversation. Claude Code installs it to ~/.claude/skills/fable-mode-sonnet/; claude.ai and Claude Desktop adopt it for the current chat and tell you how to save it permanently.
Copy install command
curl -fsSL https://spellbook.build/i/fable-mode-sonnet | bash
Drops the file into ~/.claude/skills/fable-mode-sonnet/SKILL.md. The script is plain shell — inspect it by dropping the | bash.
Download skill folder
Download .zipA fable-mode-sonnet/ folder with SKILL.md (and any supporting files) — unzip into ~/.claude/skills/.
Benchmarks
This skill isn't in a benchmarked category yet. Set metadata.type in the frontmatter to activate scorecards.
Skill content
---
name: fable-sonnet
description: >
Run fable-mode execution discipline on Claude Sonnet. Routes the task to the
@fable-worker-sonnet agent, whose definition carries the staged loop with
step-3 verification enforced hardest (Sonnet's known gap), optionally followed
by a cold @fable-verifier pass. Trigger when the user explicitly asks for
thorough/systematic/"deep work" handling on Sonnet ("fable on sonnet", "stage
this on sonnet", "deep work mode, sonnet"). The balanced default between Haiku
(cheap/fast) and Opus (peak reasoning). Do NOT use for ordinary single-pass
tasks.
---
# Fable Mode — Sonnet (v3, agent-routed)
v3 change: the worker is a real agent definition (`agents/fable-worker-sonnet.md`)
invoked by name, not a prose briefing the model can soft-ignore. Its system
prompt carries the loop and the operational rules; this skill only routes.
If a task has one obvious correct approach and fits in a single pass, skip this
loop and do it directly.
## How to run it
1. Confirm `fable-worker-sonnet` appears in the available agent types. If not,
fall back to inline: spawn a general-purpose Sonnet agent and pass it the
rules verbatim from `agents/fable-worker-sonnet.md`.
2. Spawn **@fable-worker-sonnet** via the Task tool (`subagent_type:
"fable-worker-sonnet"`). Brief it with: the task, the exact output path(s),
relevant context, and the pass condition its deliverable must satisfy —
name the check, don't leave it to taste.
3. For independent sub-parts, spawn multiple workers concurrently and merge.
Cap concurrency at a handful. Workers do not spawn workers.
4. For high-stakes deliverables, follow with **@fable-verifier**, briefed with
only the spec and the artifact path — not the worker's report.
5. Relay results and anything marked unverified.