modernize-transform

modernize-transform is a command for coding agents from ronmkr/PromptBook. It costs 17 tokens per session (702 once invoked), scanned A, original, Apache-2.0.

A code-modernization command for rewriting one older module in a newer technology stack while checking that its behavior stays the same.

In plain words
What is it for?
It plans the change, creates tests from the old module's observable behavior, and uses those tests to validate the rewritten module.
Why use it?
It reduces the risk of changing what the software does during a gradual, single-module migration.

Command

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.

agentmods
npx agentmods add commands/ronmkr/promptbook/modernize-transform
Clone the repo
git clone --depth 1 https://github.com/ronmkr/PromptBook

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-transform

README.md
[![agentmods](https://agentmods.dev/badge/commands/ronmkr/promptbook/modernize-transform.svg)](https://agentmods.dev/commands/ronmkr/promptbook/modernize-transform)
Your own site
<a href="https://agentmods.dev/commands/ronmkr/promptbook/modernize-transform"><img src="https://agentmods.dev/badge/commands/ronmkr/promptbook/modernize-transform.svg" alt="Measured on agentmods" height="20"></a>
Per session 17 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 702 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00017 $0.00702
Opus 5 $0.00009 $0.00351
Sonnet 5 $0.00003 $0.00140
Haiku 4.5 $0.00002 $0.00070

Measured 3d ago against content hash b3429785e6f4, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

modernize-transform 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 3d 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-transform.md · 79 lines

How it starts

The opening of the file, as written. The whole thing — 79 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Transform legacy/$1 module $2 into $3, with proof of behavioral equivalence.

This is a surgical, single-module transformation — one vertical slice of the strangler fig. Output goes to modernized/$1/$2/.

Step 0 — Plan (HITL gate)

Read the source module and any business rules in analysis/$1/BUSINESS_RULES.md that reference it. Then enter plan mode and present:

  • Which source files are in scope
  • The target module structure (packages/classes/files you'll create)
  • Which business rules / behaviors this module implements
  • How you'll prove equivalence (test strategy)
  • Anything ambiguous that needs a human decision NOW

Wait for approval before writing any code.

Step 1 — Characterization tests FIRST

Before writing target code, spawn the test-engineer subagent:

"Write characterization tests for legacy/$1 module $2. Read the source, identify every observable behavior, and encode each as a test case with concrete input → expected output pairs derived from the legacy logic. Target framework: <appropriate for $3>. Write to modernized/$1/$2/src/test/. These tests define 'done' — the new code must pass all of them."

Show the user the test file. Get a 👍 before proceeding.

Step 2 — Idiomatic transformation

Write the target implementation in modernized/$1/$2/src/main/.

Critical: Write code a senior $3 engineer would write from the specification, not from the legacy structure. Do NOT mirror COBOL paragraphs as methods, do NOT preserve legacy variable names like WS-TEMP-AMT-X. Use the target language's idioms: records/dataclasses, streams, dependency injection, proper error types, etc.

Include: domain model, service logic, API surface (REST controller or equivalent), and configuration. Add concise Javadoc/docstrings linking each class back to the rule IDs it implements.

Step 3 — Prove it

Run the characterization tests:

cd modernized/$1/$2 && <appropriate test command for $3>

Show the output. If anything fails, fix and re-run until green.

Read the full file on GitHub · 79 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. 3d ago First seen · 79 lines · 17 tokens per session scan A b3429785e6f4

Subscribe to this mod's changes

modernize-transform is a command published in the GitHub repository ronmkr/PromptBook (2 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 17 tokens to every session and 702 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.