Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add njt/powerups-requirements --skill reverse-engineering-requirementsgit clone --depth 1 https://github.com/njt/powerups-requirementsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/njt/powerups-requirements/reverse-engineering-requirements)<a href="https://agentmods.dev/skills/njt/powerups-requirements/reverse-engineering-requirements"><img src="https://agentmods.dev/badge/skills/njt/powerups-requirements/reverse-engineering-requirements/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/njt/powerups-requirements/reverse-engineering-requirements"><img src="https://agentmods.dev/badge/skills/njt/powerups-requirements/reverse-engineering-requirements.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00101 | $0.03080 |
| Opus 5 | $0.00051 | $0.01540 |
| Sonnet 5 | $0.00020 | $0.00616 |
| Haiku 4.5 | $0.00010 | $0.00308 |
Grade A, and why
reverse-engineering-requirements scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 286 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Reverse-Engineering Requirements
Purpose
Extract what an existing system actually does — and what it should do in a reimplementation — by reading source code, iteratively reviewing with fresh-eyes subagents, and separating genuine requirements from implementation accidents.
This is harder than greenfield elicitation because the code contains everything: requirements, design decisions, style choices, workarounds, dead code, and accidental complexity from previous technology constraints. Your job is to separate signal from noise.
Role Division
You do: Orchestrate the process. Dispatch subagents. Facilitate discussion between the human and the review findings. Draft and refine the requirements doc. Identify non-goals.
The human does: Provide context about the system's purpose and users. Confirm or reject your interpretations. Identify which behaviours are intentional vs accidental. Make priority calls.
Subagents do: Read source code with fresh eyes. Compare spec against code. Find omissions, inaccuracies, and things that don't belong. They bring no prior assumptions — that's their value.
You never: Assume every behaviour in the code is a requirement. Treat implementation details as requirements. Skip the human's judgment on what matters.
What Belongs Where
The same filtering from gathering-requirements applies, but with an extra category that dominates in reverse-engineering work:
Requirement = behaviour observable from outside. "Display client name in task list." Decision = how the system achieves it. "Store config at ~/.cu/config.json." Style = formatting/presentation. "Truncate names at 45 characters." Non-Goal = something present in the old system that we explicitly don't want. "Font size adjustment buttons (unnecessary on web — the old WinForms app couldn't resize or rescale)."
The litmus test for non-goals: "Is this behaviour in the old code because of a genuine user need, or because of a constraint that no longer exists?" If the constraint is gone, the behaviour is a non-goal candidate. Confirm with the human.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 286 lines · 101 tokens per session scan A c16827f7ccc0
reverse-engineering-requirements is a skill published in the GitHub repository njt/powerups-requirements (11 stars, last pushed 5mo ago), licensed MIT. It adds 101 tokens to every session and 3,080 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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