Best legacy modernization skills for Claude Code, Codex and other agents.

Guides systematic, test-backed refactoring in the style of Martin Fowler, moving through research, planning and small incremental changes with your approval at each phase.

luongnv89/claude-howto

Moves a legacy internal Ghost package from JavaScript and CommonJS to TypeScript and ESM in three focused commits that keep git file history intact.

TryGhost/Ghost

Measures a code port between languages or frameworks with jscpd's function-level comparison, porting tests before code and tracking what is left unmatched.

kucherenko/jscpd

Pre-launch and pre-commit audit for vibe coding projects. An agent skill from noobnooc/agent.

noobnooc/agent

Guide for organizing MSBuild infrastructure with Directory.Build.props, Directory.Build.targets, Directory.Packages.props, and Directory.Build.rsp.

microsoft/testfx

Analyzes a Rails app and builds an upgrade report with breaking changes, deprecations and step-by-step migration guides, one version at a time from Rails 2.3 through 8.1.

ombulabs/claude-code_rails-upgrade-skill

Catalog of MSBuild anti-patterns with detection rules and fix recipes.

runceel/ReactiveProperty

Picks the next CPython standard library module ready for a RustPython upgrade, skipping modules that already have an open upgrade pull request.

RustPython/RustPython

Migrate a .NET 8 project to .NET 9 and resolve all breaking changes.

dotnet/skills

Guide for modernizing and migrating MSBuild project files to SDK-style format.

microsoft/testfx

Migrate a .NET 9 project or solution to .NET 10 and resolve all breaking changes.

dotnet/skills

Catalog of MSBuild anti-patterns with detection rules and fix recipes.

microsoft/testfx

Diagnose and repair a broken or non-standard agent-second-brain install/migration.

smixs/agent-second-brain

Covers ES6+ syntax and functional patterns for refactoring older JavaScript: async/await, destructuring, spread, modules, generators and data pipelines.

wshobson/agents

基于 Martin Fowler 方法论做系统化重构。Use when users ask to refactor code, improve structure, reduce technical debt, clean up legacy code, or improve…

lhfer/claude-howto-zh-cn

Guides migrating AngularJS 1.x apps to modern Angular: choosing a strategy, running a hybrid app with ngUpgrade, and converting controllers, directives and services.

wshobson/agents

Upgrade React applications to latest versions, migrate from class components to hooks, and adopt concurrent features.

wshobson/agents

Modernizes UIKit apps for multi-window environments by replacing legacy shared-state APIs with context-appropriate modern alternatives.

superagents-lab/xcode27-skills

Migrates a direct command call in Ruby Git's Git::Lib to a Git::Commands class, as part of a Strangler Fig redesign, with a plan, legacy tests and a pull request.

ruby-git/ruby-git

Reads an undocumented codebase and writes up what it does: architecture, data flows, observed behavior as EARS requirements, and open questions to confirm.

Jeffallan/claude-skills

Test quality review drawing on twelve classic engineering books — with primary focus on xUnit Test Patterns, The Art of Unit Testing, How Google Tests Software, and Working Effectively with Legacy…

hyhmrright/brooks-lint

A skill your agent uses when modifying existing code that lacks tests and you need to document its actual current behavior before making changes -- the legacy code dilemma where you need tests to…

citypaul/.dotfiles

A skill your agent uses when the user asks to review, audit, or check the quality of ADVPL/TLPP code for TOTVS Protheus before merge or deploy -- covering best practices (RecLock/MsUnlock pairing…

thalysjuvenal/advpl-specialist

Writes snapshot-style approval tests in Python, JavaScript, TypeScript or Java, comparing output against an approved file instead of writing individual assertions.

lexler/skill-factory

Rules for continuing or remodeling a prior CraftBot building script: treat the inherited model as a found object, audit it against the brief, and track every change.

lukapiskorec/craftbot

Vietnamese edition of a systematic refactoring skill based on Martin Fowler's book, working in approved phases with small, test-backed changes.

luongnv89/claude-howto

Migrate a .NET 10 project or solution to .NET 11 and resolve all breaking changes.

dotnet/skills

DO NOT INVOKE when the primary request explicitly asks to convert, migrate, modernize, or rewrite a legacy/old-style project to SDK style; use msbuild-modernization.

dotnet/skills

Generates Protheus MVC screens in ADVPL/TLPP, with ModelDef, ViewDef, MenuDef and Browse functions for single-entity and master-detail layouts.

totvs/engpro-advpl-tlpp-skills

WORKFLOW SKILL - Safely migrates eligible Aspire 13.6+ AppHosts from legacy ProjectResource APIs to experimental DotnetProjectResource APIs after a per-resource assessment and explicit approval of…

CommunityToolkit/Aspire

Plans incremental migrations of aging systems with the strangler fig pattern, using dependency maps, rollback plans, characterization tests and gradual traffic shifts.

Jeffallan/claude-skills

Multi-agent code review that checks the current diff from multiple angles (spec compliance, bugs from two lenses, conventions/modernization, abstraction reuse, security, DB query performance, test…

sendou-ink/sendou.ink

Refactoring rules for Handsontable code: SOLID applied to plugins, Law of Demeter fixes, performance patterns and strict protection of backward compatibility.

handsontable/handsontable

Azure Communication Services CallingServer (legacy) Java SDK.

microsoft/skills

Steers C++ code toward C++20, C++23 and C++26 idioms such as smart pointers, concepts, std::expected and std::print, with a security focus.

trailofbits/skills

Produces evidence-based migration plans using the Strangler Fig pattern for monolith splits, rewrites and framework upgrades, without implementing them.

tech-leads-club/agent-skills

Scan codebases for technical debt, score severity, track trends, and generate prioritized remediation plans.

alirezarezvani/claude-skills

Domain-Driven Development workflow specialist using ANALYZE-PRESERVE-IMPROVE cycle for behavior-preserving code transformation.

modu-ai/moai-adk

A skill your agent uses when integrating legacy code, custom code, or C/C++ code into Simulink via C Function blocks.

matlab/simulink-agentic-toolkit

Modernize Go code to recent language features, standard library improvements, and idiomatic patterns.

context-labs/whip

Implement cheat codes, hidden interactions, and unlockable meta-content via time-windowed input sequence buffers, spam thresholds, look-at (dot-product) detectors, progress-% unlocks, and meta…

thedivergentai/GD-Agentic-Skills

Perform janitorial tasks on C/.NET code including cleanup, modernization, and tech debt remediation.

DynamoDS/Dynamo

Apply when creating, modifying, refactoring, debugging, testing, or reviewing TypeScript and Node.js code under bff/ in chat-gun.

HsienW/chat-gun

Modern C language features for .NET 10 and C 14. An agent skill from codewithmukesh/dotnet-claude-kit.

codewithmukesh/dotnet-claude-kit

Map application architecture — components, layers, data flow, and integration points.

EmeaAppGbb/spec2cloud

Stack configuration: local and remote imports, inheritance, deep merging, locals, vars, settings, metadata, overrides, dependencies, and modernization

cloudposse/atmos

Write or review production Go: errors, concurrency, context, types, generics, safety, tests, benchmarks, profiling, modernization, and module structure.

pedronauck/skills

Two related workflows for a locally-cloned codebase, in one skill.

github/awesome-copilot