Modernize a Legacy Codebase with AI · Execution Map
Define & Scope
Clarify what you're building and for whom.
Design
Design the right solution before building.
Build & Refine
Build, test, secure, and make it production-ready.
Ship & Validate
Ship with confidence and validate results.
Step 1 of 8
Understand the codebase
A working mental model of the existing system.
Phase
Define & Scope
Everything you need for this step
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Workflow
AI Codebase Onboarding Workflow
Get up to speed on an unfamiliar codebase in an afternoon — ground the AI in the project, have it explain the hard parts, and keep what you learn.
Resource
Onboarding Codebase — Explain Code to a New Team Member
A capable engineer with zero context on your codebase needs different explanations than a junior: conventions, vocabulary, and where everything connects — not syntax.
Tool
Project Context Builder
Define what AI should permanently know about your project — stack conventions, glossary, and never-assume rules in a profile you paste once.
Step 2 of 8
Make the architecture explicit
The existing architecture reviewed and documented.
Phase
Design
Everything you need for this step
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Workflow
AI Architecture Recovery Workflow
Recover a legacy system's architecture before you change it — package the codebase context, explain the current structure, surface the risks and seams, then document the recovered architecture.
Resource
Architecture Explanation Prompt — Layers, Boundaries, Data Flow
Explain a system's shape, not its statements: layers and their owners, boundary contracts, dependency direction, and one request traced through every handoff.
Tool
Code Explanation Prompt
Build code explanation prompts — mode, audience, and depth turn into an understanding contract that teaches, not narrates.
Step 3 of 8
Pin the behavior with tests
Tests that pin current behavior before any change.
Phase
Build & Refine
Everything you need for this step
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Workflow
AI Test Generation Workflow
Build a test suite that fails for real reasons, not green decoration — coverage across unit, integration, and edge cases, then a review for the gaps.
Resource
Unit Test Prompt — Isolation Done Right
Mock the dependencies, test the business logic, one behavior per test — the unit testing contract that bans plumbing tests.
Tool
Test Case Prompt Generator
Build test generation prompts — unit, integration, or E2E — with framework modes and edge-case coverage rules.
Step 4 of 8
Refactor safely
Cleaner structure with behavior held constant.
Phase
Build & Refine
Everything you need for this step
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Workflow
AI Code Refactoring Workflow
Restructure code you own without breaking it — change only what's worth changing, and prove with tests and a diff that behavior held.
Resource
Safe Refactoring Prompt — Zero Regression Tolerance
For code that ships weekly: a refactoring prompt where regression avoidance outranks improvement depth, log lines stay intact, and every step is rollback-friendly.
Tool
Refactor Prompt Builder
Build behavior-preserving refactor prompts — goal, risk level, and code context turn into a safe refactoring contract.
Step 5 of 8
Modernize the code
Outdated patterns brought up to current practice.
Phase
Build & Refine
Everything you need for this step
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Workflow
AI Legacy Code Modernization Workflow
Update old, risky code you didn't write — safely — by understanding and pinning its behavior in tests before you change a single line.
Resource
Legacy Code Refactor — Changing Code You Can't Fully See
Legacy code has callers you cannot see and assumptions nobody wrote down. This refactoring prompt treats every public surface as load-bearing and changes in small, verified steps.
Tool
Refactor Prompt Builder
Build behavior-preserving refactor prompts — goal, risk level, and code context turn into a safe refactoring contract.
Step 6 of 8
Review the changes
The changes reviewed for correctness and design.
Phase
Build & Refine
Everything you need for this step
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Workflow
AI Code Review Workflow
A complete AI-assisted review pass — not one prompt — that ends with ranked findings, tests guarding behavior, and a refactor plan when one is warranted.
Resource
Code Review Prompt — the Review Contract
"Review this code" gets shallow comments. The review contract gets findings with severities, a checklist, and a verdict.
Tool
Code Review Prompt Generator
Generate code review prompts for any scope — snippet, file, diff, or full pull request — with focused review rules.
Step 7 of 8
Address performance
Measured hotspots fixed, not guessed-at ones.
Phase
Build & Refine
Everything you need for this step
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Workflow
AI Performance Optimization Workflow
Speed up code that works but drags — find the actual hot path instead of guessing, understand why it's slow, optimize it, and prove with tests that you changed the speed and nothing else.
Resource
Debug Performance Problems
Measure before reasoning: find WHERE the time goes, separate latency from memory from throughput, and think at production scale.
Tool
Debugging Prompt Generator
Build debugging prompts from symptoms, environment, and reproduction steps — root cause first, fix second.
Step 8 of 8
Ship the modernized code
The modernized code shipped with a rollback path.
Phase
Ship & Validate
Everything you need for this step
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Workflow
AI Deployment & Release Workflow
Cross the gap between 'tests pass' and 'safe in production' — assess release readiness, plan the deploy and its rollback, and set up the monitoring and launch checks before you ship, not after.
Resource
Production Readiness Review Prompt
SHIP or DO NOT SHIP: twelve checks on failure modes, observability, rollback, and load — the review that happens before the incident.
Tool
Markdown Output Builder
Build prompts that produce documents in a fixed structure — headings, sections, and tables.