name

reverse-prompt-engineer

description

Reverse-engineer the prompt that most likely produced a given piece of text. Fans out many subagents that each guess a candidate prompt, runs each guess one-shot in a clean room (the executor never sees the target), scores the output against the target, then steers the best candidates over several rounds until the reproduction matches as closely as possible. Trigger when the user says "reverse engineer this prompt", "what prompt produced this", "guess the prompt", "reverse prompt engineer", or invokes /reverse-prompt-engineer. Accepts: the target text (required), and optional tuning — fanout, rounds, keep, threshold.

Reverse Prompt Engineer

Given a piece of target text, recover a prompt that — when handed to a fresh model with no other context — reproduces text as close to the target as possible. This is an evolutionary search driven by a multi-agent workflow:

Seed — N guesser agents each propose a candidate prompt, each through a different lens (a simple question, a system+user pair, a constrained task, a creative brief, a transformation, a template, a minimal prompt, a richly-specified prompt) so the starting pool is diverse.
Execute — each candidate is run one-shot in a clean room: an executor agent sees only the candidate prompt, never the target, and produces what that prompt would naturally yield. This separation is the whole point — it keeps the reproduction honest instead of leaking the answer.
Score — a judge compares each produced output against the target (content, structure, tone, length, details), returns a 0–100 similarity, and gives concrete steering advice.
Steer — the top candidates are rewritten using the judge's advice and re-evaluated. Survivors are always carried forward so a strong prompt is never lost to a worse rewrite. Loop until the best similarity clears the threshold, the rounds run out, or the token budget runs low.

The orchestration lives in workflow.js next to this file. You run it via the Workflow tool — invoking it from this skill is the explicit opt-in the tool requires.

How to run it

Get the target text. It's whatever the user wants reverse-engineered — usually pasted in their message. If they didn't include any text, ask for it before doing anything else. Don't guess.
Read any tuning options the user mentioned and fold them into the args object (all optional):
- fanout — conventional seed guessers (default 10)
- wild — unconventional "wildcard" seed guessers that try weird angles (personas, odd formats, continuations, constraint-stacking) to induce different response types (default 6)
- explore — fresh wildcard explorers injected each steer round to add novelty / break plateaus (default 3)
- rounds — max steering rounds (default 3)
- keep — survivors carried into each steer round (default 4)
- threshold — similarity (0–100) at which to stop early (default 90)
- patience — stop after this many steer rounds with no improvement (plateau stop; default 2, 0 disables)
- lengthFree / lengthScale — length-penalty knobs (defaults 30 / 80; see Scoring below)
Invoke the Workflow tool with the bundled script and the target as args. Use scriptPath so you don't have to re-send the script. The script (workflow.js) sits next to this SKILL.md, in this skill's own directory. This skill ships inside a plugin, so build the path from the skill's base directory — the absolute path printed as "Base directory for this skill" when the skill loads:
```
Workflow({
  scriptPath: "<skill base directory>/workflow.js",
  args: { text: "<the full target text>", fanout: 10, rounds: 3, threshold: 90 }
})
```
${CLAUDE_PLUGIN_ROOT}/skills/reverse-prompt-engineer/workflow.js resolves to the same file if the environment variable is available. Always pass an absolute path — do not assume the old project-relative .claude/skills/... location, which no longer exists now that this is a plugin.

If the user gave no tuning, you may pass the raw string as args (e.g. args: "<the target text>") — the script accepts either form. Preserve the target's exact formatting, whitespace, and line breaks.
Present the result the workflow returns. Lead with the recovered prompt, then show how close it got and let the user judge. A good shape:
- Recovered prompt — bestPrompt, in a fenced block so it's copy-pasteable.
- Match: similarity/100 — and one line on whatMatched / whatDiffered.
- Reproduced output — ALWAYS quote reproducedOutput back in full, verbatim, in its own fenced block. This is the actual text the clean-room model produced from the recovered prompt, and it is the single most useful thing for the user to eyeball against their original. Never paraphrase, truncate, or merely describe it — show the whole thing, even when the match is poor (a bad reproduction is exactly what the user needs to see). Only omit it if reproducedOutput is null.
- Optionally, the runnersUp prompts if they're meaningfully different and useful.
- Note the steeringRounds, candidatesEvaluated, and stoppedReason (threshold-reached / plateaued / rounds-exhausted / stopped-early) so the effort and why-it-stopped are transparent. If it plateaued, say so — more rounds won't help; suggest changing a penalty knob instead.
Offer next steps when the match is imperfect: re-run with a higher fanout/rounds, a higher threshold, or a refined target. If the user liked a runner-up better, offer to steer from that one.

Scoring: raw similarity minus two penalties

The headline similarity is not the raw judge score. The goal is to recover the short, generating instruction a person would actually type — not a long prompt that smuggles the answer in by quoting the target. So the ranked score is the judge's raw match multiplied by two code-computed penalties:

similarity = rawSimilarity × (1 − leakage) × lengthFactor

rawSimilarity (0–100) — the judge's content/structure/tone match of the clean-room output vs the target.
verbatimLeakagePct — deterministic: the % of the target's words covered by runs of 5+ consecutive words that also appear verbatim in the candidate prompt. (1 − leakage) guts prompts that quote the answer.
promptWords + length penalty — people type short prompts, so length is penalized. The first lengthFree words (default 30) are free; beyond that the score decays — a prompt lengthScale words (default 80) over the free budget keeps half its score, twice that a third, and so on. Tune via the lengthFree / lengthScale args.

Both penalties are wired through the whole loop: guessers are told to stay terse and never copy 5+-word runs, the judge is forbidden from ever advising "use this exact line," and the steerer is fed the current leakage and word count and told to cut both. When you present results, report the breakdown — e.g. "similarity 41/100 (raw 77, 0% leakage, 250 words)" — so the user sees whether the score was lost to quoting, to length, or is a genuine residual (style/specifics a short prompt legitimately can't recover).

Notes

The executor never sees the target, by design — the reproduction is honest, not a copy.
Similarity is a judge's estimate plus a code penalty, not a guarantee — describe it as "approximate match."
This burns tokens (many subagents over several rounds). For a quick, cheap pass, suggest fanout: 4, rounds: 1.

Reverse Prompt Engineer

Seed — N guesser agents each propose a candidate prompt, each through a different lens (a simple question, a system+user pair, a constrained task, a creative brief, a transformation, a template, a minimal prompt, a richly-specified prompt) so the starting pool is diverse.

Execute — each candidate is run one-shot in a clean room: an executor agent sees only the candidate prompt, never the target, and produces what that prompt would naturally yield. This separation is the whole point — it keeps the reproduction honest instead of leaking the answer.

Score — a judge compares each produced output against the target (content, structure, tone, length, details), returns a 0–100 similarity, and gives concrete steering advice.

Steer — the top candidates are rewritten using the judge's advice and re-evaluated. Survivors are always carried forward so a strong prompt is never lost to a worse rewrite. Loop until the best similarity clears the threshold, the rounds run out, or the token budget runs low.

The orchestration lives in workflow.js next to this file. You run it via the Workflow tool — invoking it from this skill is the explicit opt-in the tool requires.

How to run it

Get the target text. It's whatever the user wants reverse-engineered — usually pasted in their message. If they didn't include any text, ask for it before doing anything else. Don't guess.

Read any tuning options the user mentioned and fold them into the args object (all optional):

fanout — conventional seed guessers (default 10)
wild — unconventional "wildcard" seed guessers that try weird angles (personas, odd formats, continuations, constraint-stacking) to induce different response types (default 6)
explore — fresh wildcard explorers injected each steer round to add novelty / break plateaus (default 3)
rounds — max steering rounds (default 3)
keep — survivors carried into each steer round (default 4)
threshold — similarity (0–100) at which to stop early (default 90)
patience — stop after this many steer rounds with no improvement (plateau stop; default 2, 0 disables)
lengthFree / lengthScale — length-penalty knobs (defaults 30 / 80; see Scoring below)

Invoke the Workflow tool with the bundled script and the target as args. Use scriptPath so you don't have to re-send the script. The script (workflow.js) sits next to this SKILL.md, in this skill's own directory. This skill ships inside a plugin, so build the path from the skill's base directory — the absolute path printed as "Base directory for this skill" when the skill loads:

Workflow({
  scriptPath: "<skill base directory>/workflow.js",
  args: { text: "<the full target text>", fanout: 10, rounds: 3, threshold: 90 }
})

${CLAUDE_PLUGIN_ROOT}/skills/reverse-prompt-engineer/workflow.js resolves to the same file if the environment variable is available. Always pass an absolute path — do not assume the old project-relative .claude/skills/... location, which no longer exists now that this is a plugin.

If the user gave no tuning, you may pass the raw string as args (e.g. args: "<the target text>") — the script accepts either form. Preserve the target's exact formatting, whitespace, and line breaks.

Present the result the workflow returns. Lead with the recovered prompt, then show how close it got and let the user judge. A good shape:

Recovered prompt — bestPrompt, in a fenced block so it's copy-pasteable.
Match: similarity/100 — and one line on whatMatched / whatDiffered.
Reproduced output — ALWAYS quote reproducedOutput back in full, verbatim, in its own fenced block. This is the actual text the clean-room model produced from the recovered prompt, and it is the single most useful thing for the user to eyeball against their original. Never paraphrase, truncate, or merely describe it — show the whole thing, even when the match is poor (a bad reproduction is exactly what the user needs to see). Only omit it if reproducedOutput is null.
Optionally, the runnersUp prompts if they're meaningfully different and useful.
Note the steeringRounds, candidatesEvaluated, and stoppedReason (threshold-reached / plateaued / rounds-exhausted / stopped-early) so the effort and why-it-stopped are transparent. If it plateaued, say so — more rounds won't help; suggest changing a penalty knob instead.

Offer next steps when the match is imperfect: re-run with a higher fanout/rounds, a higher threshold, or a refined target. If the user liked a runner-up better, offer to steer from that one.

Scoring: raw similarity minus two penalties

similarity = rawSimilarity × (1 − leakage) × lengthFactor

rawSimilarity (0–100) — the judge's content/structure/tone match of the clean-room output vs the target.

verbatimLeakagePct — deterministic: the % of the target's words covered by runs of 5+ consecutive words that also appear verbatim in the candidate prompt. (1 − leakage) guts prompts that quote the answer.

promptWords + length penalty — people type short prompts, so length is penalized. The first lengthFree words (default 30) are free; beyond that the score decays — a prompt lengthScale words (default 80) over the free budget keeps half its score, twice that a third, and so on. Tune via the lengthFree / lengthScale args.

Notes

The executor never sees the target, by design — the reproduction is honest, not a copy.

Similarity is a judge's estimate plus a code penalty, not a guarantee — describe it as "approximate match."

This burns tokens (many subagents over several rounds). For a quick, cheap pass, suggest fanout: 4, rounds: 1.