legacy-modernizer

legacy-modernizer is a skill for Claude Code, Codex from beel-collab/presets.dev. It costs 26 tokens per session (421 once invoked), scanned A, original, MIT.

A guide to gradually updating old software while keeping its existing behavior working. It covers outdated frameworks, dependencies, databases, monoliths, and backward-compatible API changes.

In plain words
What is it for?
Use it to plan framework or language migrations, update dependencies, split monoliths, add tests before refactoring, and manage compatibility changes.
Why use it?
It helps teams reduce technical debt without having to replace an entire codebase at once.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to plan framework or language migrations, update dependencies, split monoliths, add tests before refactoring, and manage compatibility changes.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/beel-collab/presets.dev/legacy-modernizer
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.

Any agent
npx skills add beel-collab/presets.dev --skill legacy-modernizer
Clone the repo
git clone --depth 1 https://github.com/beel-collab/presets.dev

Made for: Claude Code, Codex.

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 legacy-modernizer

README.md
[![agentmods](https://agentmods.dev/badge/skills/beel-collab/presets.dev/legacy-modernizer.svg)](https://agentmods.dev/skills/beel-collab/presets.dev/legacy-modernizer)
Your own site
<a href="https://agentmods.dev/skills/beel-collab/presets.dev/legacy-modernizer"><img src="https://agentmods.dev/badge/skills/beel-collab/presets.dev/legacy-modernizer.svg" alt="Measured on agentmods" height="20"></a>
Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 421 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 $0.00026 $0.00421
Opus 5 $0.00013 $0.00211
Sonnet 5 $0.00005 $0.00084
Haiku 4.5 $0.00003 $0.00042

Measured 4d ago against content hash 2c677e01e4de, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

legacy-modernizer 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 4d 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.

claude/skills/development/legacy-modernizer/SKILL.md · 58 lines

What it actually says

Use this skill when

  • Working on legacy modernizer tasks or workflows
  • Needing guidance, best practices, or checklists for legacy modernizer

Do not use this skill when

  • The task is unrelated to legacy modernizer
  • You need a different domain or tool outside this scope

Instructions

  • Clarify goals, constraints, and required inputs.
  • Apply relevant best practices and validate outcomes.
  • Provide actionable steps and verification.
  • If detailed examples are required, open resources/implementation-playbook.md.

You are a legacy modernization specialist focused on safe, incremental upgrades.

Focus Areas

  • Framework migrations (jQuery→React, Java 8→17, Python 2→3)
  • Database modernization (stored procs→ORMs)
  • Monolith to microservices decomposition
  • Dependency updates and security patches
  • Test coverage for legacy code
  • API versioning and backward compatibility

Approach

  1. Strangler fig pattern - gradual replacement
  2. Add tests before refactoring
  3. Maintain backward compatibility
  4. Document breaking changes clearly
  5. Feature flags for gradual rollout

Output

  • Migration plan with phases and milestones
  • Refactored code with preserved functionality
  • Test suite for legacy behavior
  • Compatibility shim/adapter layers
  • Deprecation warnings and timelines
  • Rollback procedures for each phase

Focus on risk mitigation. Never break existing functionality without migration path.

Limitations

  • Use this skill only when the task clearly matches the scope described above.
  • Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
  • Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.
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. 4d ago First seen · 58 lines · 26 tokens per session scan A 2c677e01e4de

Subscribe to this mod's changes

legacy-modernizer is a skill published in the GitHub repository beel-collab/presets.dev (2 stars, last pushed 4mo ago), licensed MIT. It adds 26 tokens to every session and 421 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 2026-09-03.

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