Say "fable-mode" (or "operate carefully," or "high-judgment mode" or "think like fable") in a Claude Code or Codex session, and one line buried in the skill file does most of the work: "Never promote 'plausible' to 'confirmed' in your summary." That single rule is the whole philosophy in miniature — don't let something that merely looks right pass as something that was checked.
Fable-mode is not a tool, a model swap, or a set of new commands. It's a behavioral overlay — a skill file at ~/.claude/skills/fable-mode/SKILL.md
or ~/.codex/skills/fable-mode/SKILL.md
or any other agent you use, that gets loaded into the turn and changes how the agent scopes work, verifies its own claims, and reports results. Nothing about what Agents can do changes. What changes is the discipline around using it.
The skill is organized into seven blocks, and each one targets a specific failure mode that shows up in normal agent use:
Judgment before action. The first move is classification: is this a question, a problem description, or a change request? For the first two, the deliverable is an assessment — investigate and stop, don't start editing files nobody asked you to edit. Irreversible actions (deletes, pushes, overwrites) require a stop-and-confirm, and specifically: "before deleting or overwriting anything, actually look at the target."
Verification as the non-negotiable core. This is the section that does the heavy lifting. Every "done" claim needs evidence produced after the last edit — a test run before your final change proves nothing about your final change. Claims get graded on a three-tier scale: Confirmed (you ran it and saw the result), Plausible (the code reads right but you haven't executed it), Assumed (inherited from the user's description). The rule is that you report the grade you actually earned, not the one that sounds better.
Reasoning habits. Hold two hypotheses before committing to a diagnosis. Treat your memory of a library's API as a prior, not a fact, and check the installed version when correctness depends on it. When a result contradicts what you expected, that's flagged as "the most information-dense moment of the task" — chase it instead of smoothing over it.
Anti-patterns as hard stops. Eight explicit bans, including "declare success without a post-change verification run," "fix a bug you can't explain," and "hedge a known failure ('should work now') — either you verified it or you report it as unverified."
The skill closes with a five-item checklist the agent is meant to run before ending any turn — essentially a self-audit against the rules above.
Turn fable-mode on for the tasks where being wrong is expensive: schema migrations, auth changes, anything touching shared code, or a bug you don't yet understand. Expect the final report to distinguish what was actually tested from what merely compiles, expect fewer "while I was in there, I also…" surprises in the diff, and expect the agent to stop and ask before anything destructive rather than assuming consent. Don't expect it to make trivial tasks faster — for a one-line CSS fix, the skill's own "match depth to stakes" rule means it should behave close to normal anyway. The gain isn't speed; it's a report you can trust at face value, on the tasks where that trust is worth paying the extra verification steps for.
Feel free to contribute