AI Code Review vs Linters: What's the Difference and Do You Need Both?
Teams adding Merlin AI Code Review to their pipeline often ask: "We already have ESLint/Clippy/Rubocop — do we still need AI review?" The short answer is yes, and here's exactly why: linters and AI code review operate at fundamentally different levels of abstraction.
What linters catch
Linters perform static analysis — they check code against a set of rules without understanding what the code is supposed to do. They excel at:
- Syntax errors — unclosed brackets, invalid tokens, type mismatches
- Style enforcement — naming conventions, indentation, import ordering
- Known anti-patterns — using
==instead of===in JavaScript,unwrap()without justification in Rust - Simple dead code — unused variables, unreachable branches
- Formatting — line length, trailing whitespace
Linters are fast, deterministic, and cheap. They should run before AI review and before human review — catching mechanical issues in milliseconds.
What AI code review catches
AI review operates at the semantic level — it understands what the code does, not just how it looks. It catches:
- Logic bugs — off-by-one errors, incorrect conditional logic, race conditions that linters can't detect
- Security vulnerabilities — SQL injection, XSS, authentication bypasses — context-dependent issues that require understanding the code's purpose
- Architectural concerns — inappropriate coupling, violation of SOLID principles, problematic abstractions
- Cross-file impact — with RAG, how a change in one file affects other parts of the codebase
- Missing tests — identifying which changed logic isn't covered by tests
- Documentation gaps — where public APIs lack documentation
- Business logic errors — code that compiles and lints cleanly but does the wrong thing
The coverage gap between them
| Issue type | Linter | AI review |
|---|---|---|
| Syntax errors | ✅ | ✅ |
| Style violations | ✅ | ✅ |
| Logic bugs | ❌ | ✅ |
| Security vulnerabilities | ⚠️ (simple patterns) | ✅ (contextual) |
| Missing tests | ❌ | ✅ |
| Architecture concerns | ❌ | ✅ |
| Cross-file impact | ❌ | ✅ (with RAG) |
| Documentation gaps | ⚠️ (presence, not quality) | ✅ |
| Business logic errors | ❌ | ✅ |
The right pipeline order
Run them in sequence, fastest first:
- Format checks (Prettier, gofmt, rustfmt) — milliseconds
- Linter (ESLint, Clippy, Rubocop) — seconds
- Merlin AI Code Review — 30–60 seconds, in parallel with tests
- Tests — minutes
- Human review — inherits pre-cleaned PRs
This pipeline catches issues at the cheapest possible point: formatting issues before linting, linting issues before AI review, AI-caught issues before human review. Each layer is smarter and more expensive than the last, so earlier layers should catch everything they can.