GuideIntermediate
Refactoring & Legacy Code with Claude Code
Master working with existing codebases using Claude Code. Learn to onboard much faster with a systematic method, explore codebases with the Explore subagent, coordinate multi-file refactoring, migrate frameworks, and manage context for large projects. Most of a developer's work happens in code that already exists, and these are the skills for it.
- lessons
- 43
- modules
- 8
- available in
- English · Spanish
- certificate
- Yes
- access
- Free
What you'll be able to do
- Onboard to unknown codebases much faster using systematic Claude Code exploration
- Use the Explore subagent for read-only investigation: search by intent without loading up your session
- Generate architecture diagrams, dependency maps, and flow analysis with Claude Code
- Execute coordinated multi-file refactoring with automated cross-file reference updates
- Plan and execute framework migrations (Flask→FastAPI) using strangler fig pattern
- Manage context for large projects: chunking strategies, CLAUDE.md, how to use (and measure) the 1M token window
- Identify and eliminate tech debt with incremental refactoring assisted by AI
- Migrate a real legacy project end-to-end with documentation and regression tests
What you need to bring
It's for you if...
- Developers joining existing teams who need to understand large codebases quickly
- Teams with accumulated tech debt looking for efficient modernization strategies
- Professionals working with large projects (50K-500K+ lines) who need context management skills
- Developers migrating frameworks or languages who want AI-assisted step-by-step execution
- Anyone who spends most of their time maintaining, understanding, or improving existing code
Requirements and materials
- Completed Claude Code Foundations (or equivalent Claude Code experience)
- Completed Testing with Claude Code: tests are the safety net for every refactoring
- Intermediate Python (functions, classes, modules, imports, error handling)
- Git proficiency (branches, merging, pull requests, conflict resolution)
- No prior refactoring methodology experience required (taught from scratch)
The syllabus, module by module
Open any of them to see its lessons.
What people usually ask
No limit. It's a free guide: come in whenever you like, as often as you like.
No. Modules run from easier to harder, but you can jump to the one you need. Progress is saved per lesson.
Whatever is needed is listed under “What you need to bring”, above. If nothing is listed there, you can start from zero.
In the WhatsApp group, and every two weeks there's a live with an instructor where questions get worked through.
Yes. When you finish every lesson you get a statement of completion. Pass the guide's certification exam and it becomes a certificate, with a verifiable code you can share on LinkedIn.
Start whenever you like
What students say
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