prompting-fable

name

prompting-fable

description

How to prompt Fable (and other next-generation frontier agentic models) to get outsized results — distilled from Matt Shumer's "How I Prompt Fable." Use when handing a big build/creative/engineering task to a top-tier model, when the user asks "help me write a prompt for X", mentions Fable, /loop, or ultracode, or says "I can't get results like the demos." Shifts prompting from step-by-step instructions to goal + house rules + a hard self-checkable bar + looping.

Prompting Fable

Distilled from Matt Shumer's "How I Prompt Fable." The core shift: next-gen models get WORSE when you spoon-feed steps and BETTER when you hand a goal and fence it with rules + a hard bar. Prompt Fable like the current models and you get current-model results. Change the approach and the ceiling lifts.

Source guide (readable by agents): https://simplemarkdowneditor.com/pub/IbaCrTjLJT?key=uQOQ2NPO3TTUSXyYDjyLf

The 7 moves

1. Give it the goal, not the steps

Hand it big, sweeping, underspecified work — the way you'd hand a goal to a brilliant person you trust. Every step you dictate overrides its judgment with yours, and yours is usually worse. Don't specify how. Specify what and why.

2. Set house rules so you can trust it

An underspecified goal is safe only when fenced by a few rules it can't cross. House rules = the handful of things that must always be true regardless of path.

• Example rule: "Don't hard-code special cases (no regex for one edge case) — describe the behavior in the system prompt and let the model reason."
• For protection: assign a sub-agent one job — check the work against the house rules before anything ships.

3. Give it a real bar for "done"

Adjectives ("high quality") make it stop at its idea of good enough — lower than yours. Replace adjectives with a concrete, self-checkable test.

• Write the test yourself when you can: "a stranger can't tell our render from the real photo."
• When you can't measure it, hand THAT problem to the model — let it invent the measuring stick (e.g. it turned a screen recording into a heat map of motion and matched against it).
• Never let the builder grade itself. The build agent is biased and has a trajectory of justifications. Spin up a SEPARATE sub-agent with a fresh context window, point it at the real output (actual pixels, actual running app), and task it to PROVE the work is not passing.

4. Loop it until it hits the bar (especially creative work)

Put it on a loop: build → check against the bar → find the biggest gap → close it → repeat. For hours or days. The model never gets to decide it's finished — there's always a next gap. It stops when you say so, or when it genuinely can't find anything to fix. Use /loop.

• Progress trick: have it post progress (screenshots, notes) to a live doc so you can watch from your phone and inject comments mid-run.

5. Let it build on what you've already done

Old work is fuel. Once you have one great artifact, point new work at it: "here's the code, here's the quality bar, match this and go beyond it." It can also read TRACES of prior agent sessions — "read the forest traces and learn what worked" beats re-explaining the approach.

6. Get out of its way

Every forced stop costs time. Clear obstacles up front:

• Give a BUDGET instead of per-use permission for paid services.
• Tell it where keys/credentials live.
• In writing: "make your own calls; only come back if truly blocked or it's a decision only I can make."
• Exception: for huge, consequential builds, demand a PLAN first and have it ask everything it's unsure about up front. Once the plan is settled, it runs without stopping.

7. Two ways to run it

• Engineering — run a team. Several sessions pull tasks from a list/board, each triple-checks its own work with sub-agents and opens a PR with evidence. One dedicated integrator merges PRs, runs everything, tests like a real user, keeps it green. Overlapping features: one watches the other's traces to stay compatible.
• Creative — momentum + detail. Same loop, same hard bar, but fan out sub-agents to perfect individual pieces (one per tree in a forest). Run several separate attempts, keep the best, carry what worked into the next round.

When to spend on ultracode

Rarely. A good loop with an ambitious goal usually gets there without it. It earns its cost on FOUNDATIONS — a new system you'll build on for months, where a good base makes everything easier and a bad one makes everything harder forever. For that, and pretty much only that, pay for ultracode.

How to actually use this skill

When the user asks for help prompting Fable (or any frontier agentic model), draft a prompt with this shape:

GOAL: <the outcome, underspecified — no step-by-step>
WHY: <context so it can make good judgment calls>
HOUSE RULES:
  - <invariant 1 it must never break>
  - <invariant 2>
DONE = <a concrete, self-checkable test — no adjectives>
GRADING: a fresh separate sub-agent must try to prove this is NOT done,
         checking the real output, before anything ships.
LOOP: keep closing the biggest gap against DONE until it passes or you're told to stop.
AUTONOMY: budget $<X>; keys at <location>; make your own calls; only stop if truly blocked.
BUILD ON: <links to prior artifacts / traces to match and exceed>

Then pressure-test the user's draft: does it dictate steps (cut them)? does it use adjectives instead of a bar (replace them)? does the builder grade itself (add a fresh-context adversarial checker)? is there a loop and a stop condition?