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axum-syntax-handlers

Fix Axum handler compile errors by correcting signatures and extractor ordering.

Updated May 20, 2026
Search Tags:#rust#handlers#axum#intoresponse#extractors#compile-time diagnostics#debug_handler
One-click install
npx skills add https://github.com/Impertio-Studio/Axum-Claude-Skill-Package --skill axum-syntax-handlers
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: axum-syntax-handlers
Source: https://github.com/Impertio-Studio/Axum-Claude-Skill-Package/tree/main/skills/source/axum-syntax/axum-syntax-handlers
Command: npx skills add https://github.com/Impertio-Studio/Axum-Claude-Skill-Package --skill axum-syntax-handlers

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill includes references (resource) components.

What problem does it solve?

Axum often rejects a handler with an opaque compile-time error like the Handler trait bound not being satisfied, even when the function looks close to correct; this Skill helps you identify and fix the exact mismatch in the handler signature.

Core Features & Use Cases

  • Diagnose handler eligibility: Ensures the handler is an async function (or async closure) whose arguments are valid extractors and whose body extractor is positioned last.
  • Validate return types: Enforces that the return value implements IntoResponse, including Result-style handlers for typed failures.
  • Prevent Send-related rejection: Avoids !Send futures caused by holding non-Send values (e.g., std::sync::MutexGuard, Rc, RefCell borrows) across await points.
  • Control extractor arity: Prevents the “more than 16 arguments” failure by guiding extractor bundling into a custom struct implementing FromRequestParts.
  • Fallback for debugging: Directs you to apply #[debug_handler] first to get precise diagnostics for the failing argument or return type.

Quick Start

Ask the AI to rewrite your handler function so it compiles on Axum 0.8 by using only extractor arguments (with a single body extractor last), an IntoResponse-compatible return type, and #[debug_handler] when needed.

Frequently Asked Questions about axum-syntax-handlers

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
Why does my Axum handler fail to compile with a Handler trait bound not satisfied error?▼

Axum handler compile errors occur when arguments are not valid extractors, the body extractor is not positioned last, or the return type does not implement IntoResponse. Correcting the handler signature, extractor ordering, and return type resolves the rejection.

How do I fix a non-Send future error in an Axum async handler?▼

To fix a non-Send future error in an Axum handler, ensure you do not hold non-Send values like std::sync::MutexGuard, Rc, or RefCell borrows across await points. Restructuring the async function to drop these values before awaiting resolves the issue.

How many extractors can I use in an Axum handler function?▼

Axum handlers support a maximum of 16 extractor arguments. If you exceed the 16-argument limit, bundle multiple extractors into a custom struct implementing FromRequestParts to pass the compile check.

How do I get better compile-time diagnostics for an Axum handler rejection?▼

To get better compile-time diagnostics for an Axum handler rejection, apply the #[debug_handler] attribute to your async function. This pinpoints the exact failing argument or invalid return type causing the Handler trait bound failure.

Does Axum 0.8 require async functions for all handlers?▼

Yes, Axum 0.7 and 0.8 require handlers to be async functions or async closures. Arguments must be valid extractors, only a single FromRequest body extractor is allowed last, and the return type must implement IntoResponse.

Can I return a Result type from an Axum handler?▼

Yes, you can return a Result type from an Axum handler as long as both the success and error variants implement IntoResponse. This allows typed failure handling while satisfying the Handler blanket implementation requirements.

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