---
name: axum-code-review
description: Reviews axum web framework code for routing patterns, extractor usage, middleware, state management, and error handling. Use when reviewing Rust code that uses axum, tower, or hyper for HTTP services. Covers axum 0.7+ patterns including State, Path, Query, Json extractors.
---
# Axum Code Review
Review Workflow
1. **Check Cargo.toml** — Note axum version (0.6 vs 0.7+ have different patterns), tower, tower-http features
2. **Check routing** — Route organization, method routing, nested routers
3. **Check extractors** — Order matters (body extractors must be last), correct types
4. **Check state** — Shared state via `State<T>`, not global mutable state
5. **Check error handling** — `IntoResponse` implementations, error types
Output Format
Report findings as:
[FILE:LINE] ISSUE_TITLE
Severity: Critical | Major | Minor | Informational
Description of the issue and why it matters.
Quick Reference
| Issue Type | Reference |
|------------|-----------|
| Route definitions, nesting, method routing | [references/routing.md](references/routing.md) |
| State, Path, Query, Json, body extractors | [references/extractors.md](references/extractors.md) |
| Tower middleware, layers, error handling | [references/middleware.md](references/middleware.md) |
Review Checklist
Routing
[ ] Routes organized by domain (nested routers for `/api/users`, `/api/orders`)[ ] Fallback handlers defined for 404s[ ] Method routing explicit (`.get()`, `.post()`, not `.route()` with manual method matching)[ ] No route conflicts (overlapping paths with different extractors)Extractors
[ ] Body-consuming extractors (`Json`, `Form`, `Bytes`) are the LAST parameter[ ] `State<T>` requires `T: Clone` — typically `Arc<AppState>` or direct `Clone` derive[ ] `Path<T>` parameter types match the route definition[ ] `Query<T>` fields are `Option` for optional query params with `#[serde(default)]`[ ] Custom extractors implement `FromRequestParts` (not body) or `FromRequest` (body)State Management
[ ] Application state shared via `State<T>`, not global mutable statics[ ] Database pool in state (not created per-request)[ ] State contains only shared resources (pool, config, channels), not request-specific data[ ] `Clone` derived or manually implemented on state typeError Handling
[ ] Handler errors implement `IntoResponse` for proper HTTP error codes[ ] Internal errors don't leak to clients (no raw error messages in 500 responses)[ ] Error responses use consistent format (JSON error body with code/message)[ ] `Result<impl IntoResponse, AppError>` pattern used for handlersMiddleware
[ ] Tower layers applied in correct order (outer runs first on request, last on response)[ ] `tower-http` used for common concerns (CORS, compression, tracing, timeout)[ ] Request-scoped data passed via extensions, not global state[ ] Middleware errors don't panic — they return error responsesSeverity Calibration
Critical
Body extractor not last in handler parameters (silently consumes body, later extractors fail)SQL injection via path/query parameters passed directly to queriesInternal error details leaked to clients (stack traces, database errors)Missing authentication middleware on protected routesMajor
Global mutable state instead of `State<T>` (race conditions)Missing error type conversion (raw `sqlx::Error` returned to client)Missing request timeout (handlers can hang indefinitely)Route conflicts causing unexpected 405sMinor
Manual route method matching instead of `.get()`, `.post()`Missing fallback handler (default 404 is plain text, not JSON)Middleware applied per-route when it should be global (or vice versa)Missing `tower-http::trace` for request loggingInformational
Suggestions to use `tower-http` layers for common concernsRouter organization improvementsSuggestions to add OpenAPI documentation via `utoipa` or `aide`Valid Patterns (Do NOT Flag)
**`#[axum::debug_handler]` on handlers** — Debugging aid that improves compile error messages**`Extension<T>` for middleware-injected data** — Valid pattern for request-scoped values**Returning `impl IntoResponse` from handlers** — More flexible than concrete types**`Router::new()` per module, merged in main** — Standard organization pattern**`ServiceBuilder` for layer composition** — Tower pattern, not over-engineering**`axum::serve` with `TcpListener`** — Standard axum 0.7+ server setupBefore Submitting Findings
Load and follow `beagle-rust:review-verification-protocol` before reporting any issue.