Fableit

Fableit teaches your AI coding assistant to work like a careful senior engineer. It is a small ruleset you install once. After that, the model checks facts before stating them, reads the code before changing it, verifies its own work before reporting, and tells you honestly what it did and did not do.

It packages the engineering process of Claude Fable 5 (retired 2026-07-07) so that any model in any agent tool can run it: Claude Code, OpenCode, Cursor, Codex CLI, Gemini CLI, aider, and anything else that reads an instructions file.

Where this comes from

Published analysis found that Fable 5's lead over older models was not raw intelligence on short tasks. It was learnable behavior:

• Goal persistence: after every error or detour, re-anchor on the original goal instead of drifting.
• Killing incorrect beliefs: treat your current theory as a hypothesis and drop it the moment evidence contradicts it.
• Self-verification as a reflex: test your own work before presenting it.
• Keeping looking before asking: exhaust what you can find yourself before interrupting the human with a question.
• Effort allocation: think hard on the genuinely hard parts, move fast through the mechanical parts.
• Memory discipline: with persistent memory, Fable improved 3x more than Opus.

Fableit injects those behaviors as an always-on ruleset: ground → comprehend → reason → design → execute → verify → report. In plain terms: check the facts, read the code, think, plan, do the work, test it, then report honestly.

How it works

Two files matter, and they say the same thing at different sizes:

• SKILL.md is the full blueprint, written for the model to read when it needs the complete process.
• hooks/fableit-instructions.js holds the condensed ruleset that gets injected into every session. One source of truth for every host.

Once installed, the ruleset is added to the model's instructions automatically at the start of every session. You never have to remember to turn it on.

Install

Fableit is published on npm under two names with identical contents: @seedexr/fableit, the canonical package owned by the SeedeXR organization, and fableit, the short name used in the commands below. Install whichever you prefer.

Claude Code

Recommended: the installer wires everything (hooks, skill, statusline badge).

npx fableit

# or straight from GitHub:
npx github:SeedeXR/fableit

What the installer does, step by step:

• Adds three hooks to settings.json in your Claude config dir:
  • SessionStart injects the ruleset when a session begins,
  • SubagentStart makes sub-agents follow the same rules,
  • UserPromptSubmit tracks level switches like /fableit ultra.
• Installs the fableit skill and copies the package to ~/.claude/fableit.
• If you have no statusline, adds a [FABLEIT] / [FABLEIT:ULTRA] badge so you can see at a glance that it is active (a bash script, skipped on Windows).

It never overwrites an existing statusline, and it refuses to touch a settings.json it cannot parse. Restart Claude Code or /clear to activate.

Alternative: install through the plugin marketplace.

/plugin marketplace add SeedeXR/fableit
/plugin install fableit@fableit

Skill only (no hooks, load on demand with /fableit):

git clone https://github.com/SeedeXR/fableit ~/.claude/skills/fableit

To remove everything the installer added (hooks, skill, flag, OpenCode entry, installed copy), while leaving your other settings untouched:

npx fableit uninstall

OpenCode

npx fableit opencode

This wires the plugin into ~/.config/opencode/opencode.json, pointing at the stable ~/.claude/fableit copy. Or: npm i -g fableit and add "plugin": ["fableit"] to your opencode.json. The plugin appends the ruleset to every turn's system prompt and registers the /fableit command.

Other tools (Cursor, Codex CLI, Copilot, Gemini CLI, Windsurf, aider, ...)

Any tool that reads an instructions file can run fableit: append the ruleset to whatever file your tool loads.

npx fableit print >> AGENTS.md      # Codex, aider, many others
npx fableit print >> .cursorrules   # Cursor
npx fableit print >> GEMINI.md      # Gemini CLI
npx fableit print lite              # smaller variant, to stdout

Levels

Fableit ships three intensity levels. Each level includes everything from the one before it and adds more.

Level	Adds
lite	Grounding/zero-hallucination protocol, comprehension-first, the solution ladder, root-cause debugging, verify-before-report, honest reporting.
full (default)	+ goal persistence, effort allocation & sub-agent orchestration, deciding vs asking, session rhythm & memory discipline.
ultra	+ a mandatory verification gate: every claim in the final report must trace to observed evidence, and reports end with a "Verified:" list.

Which one to pick: lite is the core discipline and the cheapest in tokens. full, the default, adds the behaviors that matter on long tasks. ultra adds a strict "no evidence, no claim" gate, built for models that tend to guess confidently.

Switch anytime with /fableit lite|full|ultra|off (both Claude Code and OpenCode). Turn it off with stop fableit or normal mode. All states, including off, persist until changed. Set the default level with the FABLEIT_DEFAULT_MODE env var or ~/.config/fableit/config.json ({"defaultMode": "ultra"}).

Why it helps older models

The behaviors above are process, not parameters. A model that re-anchors on the goal after every error, refuses to state unobserved facts, and runs a verification gate before reporting closes most of the gap this ruleset was distilled from. The ultra gate exists precisely for models that hallucinate confidently: no evidence, no claim.

Development

npm test        # node --test tests/*.test.js (unit + installer integration)

PRs welcome. Keep the spirit: it is a decision process, not a style guide. Every addition should be a behavior a model can actually execute, grounded in something observed or published, not vibes.