modernize-extract-rules

modernize-extract-rules is a command for Claude Code from ronmkr/PromptBook. It costs 14 tokens per session (764 once invoked), scanned A, original, Apache-2.0.

A code-analysis command that finds business rules hidden in an older system and writes them as readable, testable specifications.

In plain words
What is it for?
It helps document formulas, validation and eligibility checks, and status or lifecycle changes, either across a system or in selected files.
Why use it?
It makes important decisions easier to understand and preserves knowledge that may otherwise remain buried in code or with particular engineers.

Command for Claude Code

Written for Claude Code: argument-hint in frontmatter. Also seen: mentions subagents; positional $N argument.

Good fit It helps document formulas, validation and eligibility checks, and status or lifecycle changes, either across a system or in selected files.

Compare 6 commands from other repositories ↓
Install with agentmods
npx agentmods add commands/ronmkr/promptbook/modernize-extract-rules
Install

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.

Clone the repo
git clone --depth 1 https://github.com/ronmkr/PromptBook

Made for: Claude Code.

Wrote 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.

agentmods badge for modernize-extract-rules

README.md
[![agentmods](https://agentmods.dev/badge/commands/ronmkr/promptbook/modernize-extract-rules.svg)](https://agentmods.dev/commands/ronmkr/promptbook/modernize-extract-rules)
Your own site
<a href="https://agentmods.dev/commands/ronmkr/promptbook/modernize-extract-rules"><img src="https://agentmods.dev/badge/commands/ronmkr/promptbook/modernize-extract-rules.svg" alt="Measured on agentmods" height="20"></a>
Per session 14 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 764 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00014 $0.00764
Opus 5 $0.00007 $0.00382
Sonnet 5 $0.00003 $0.00153
Haiku 4.5 $0.00001 $0.00076

Measured 7d ago against content hash d0a7f765bb83, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

modernize-extract-rules 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 7d 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.

plugins/standard/code-modernization/commands/modernize-extract-rules.md · 77 lines

How it starts

The opening of the file, as written. The whole thing — 77 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Extract the business rules embedded in legacy/$1 into a structured, testable specification — the institutional knowledge that's currently locked in code and in the heads of engineers who are about to retire.

Scope: if a module pattern was given ($2), focus there; otherwise cover the entire system. Either way, prioritize calculation, validation, eligibility, and state-transition logic over plumbing.

Method

Spawn three business-rules-extractor subagents in parallel, each assigned a different lens. If $2 is non-empty, include "focusing on files matching $2" in each prompt.

  1. Calculations — "Find every formula, rate, threshold, and computed value in legacy/$1. For each: what does it compute, what are the inputs, what is the exact formula/algorithm, where is it implemented (file:line), and what edge cases does the code handle?"

  2. Validations & eligibility — "Find every business validation, eligibility check, and guard condition in legacy/$1. For each: what is being checked, what happens on pass/fail, where is it (file:line)?"

  3. State & lifecycle — "Find every status field, state machine, and lifecycle transition in legacy/$1. For each entity: what states exist, what triggers transitions, what side-effects fire?"

Synthesize

Merge the three result sets. Deduplicate. For each distinct rule, write a Rule Card in this exact format:

### RULE-NNN: <plain-English name>
**Category:** Calculation | Validation | Lifecycle | Policy
**Priority:** P0 | P1 | P2
**Source:** `path/to/file.ext:line-line`
**Plain English:** One sentence a business analyst would recognize.
**Specification:**
  Given <precondition>
  When  <trigger>
  Then  <outcome>
  [And  <additional outcome>]
**Parameters:** <constants, rates, thresholds with their current values>
**Edge cases handled:** <list>
**Suspected defect:** <optional — legacy behavior that looks wrong; decide preserve-vs-fix during transform>
**Confidence:** High | Medium | Low — <why; if < High, state the exact SME question>

Read the full file on GitHub · 77 lines

Changes

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.

  1. 7d ago First seen · 77 lines · 14 tokens per session scan A d0a7f765bb83

Subscribe to this mod's changes

modernize-extract-rules is a command published in the GitHub repository ronmkr/PromptBook (2 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 14 tokens to every session and 764 once invoked, about $0.0001 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 2026-08-31.