What causes "Unsupported server function HTTP method: {method:?}" in leptos-rs/leptos?

Change the server function to use GET, POST, PUT, DELETE, or PATCH (the default is POST).

Unsupported server function HTTP method: {method:?}

Error message

Unsupported server function HTTP method: {method:?}

What it means

leptos's Axum integration builds a route for each server function based on the HTTP method stored in the server function's metadata. Only GET, POST, PUT, DELETE, and PATCH are mapped to Axum's method routers; any other method causes an immediate panic while constructing the router.

Source

Thrown at integrations/axum/src/lib.rs:1842

        // register server functions
        for (path, method) in server_fn::axum::server_fn_paths() {
            let cx_with_state = cx_with_state.clone();
            let handler = move |req: Request<Body>| async move {
                handle_server_fns_with_context(cx_with_state, req).await
            };

            if !excluded.contains(path) {
                router = router.route(
                    path,
                    match method {
                        Method::GET => get(handler),
                        Method::POST => post(handler),
                        Method::PUT => put(handler),
                        Method::DELETE => delete(handler),
                        Method::PATCH => patch(handler),
                        _ => {
                            panic!(
                                "Unsupported server function HTTP method: \
                                 {method:?}"
                            );
                        }
                    },
                );
            }
        }

        // register router paths
        for listing in paths.iter().filter(|p| !p.exclude) {
            let path = listing.path();

            for method in listing.methods() {
                let cx_with_state = cx_with_state.clone();
                let cx_with_state_and_method = move || {
                    provide_context(method);
                    cx_with_state();

View on GitHub (pinned to 32d20f6c9d)

Solutions

Change the server function to use GET, POST, PUT, DELETE, or PATCH (the default is POST).
If a custom method is truly required, add a match arm mapping it to the corresponding Axum method-router helper before the catch-all panic.
Verify the config passed to #[server(...)] (e.g. `method = ...`) only uses supported verbs.

Example fix

// before
#[server(FetchThing, "/api")]
#[cfg_attr(feature = "ssr", server(method = HEAD))]
async fn fetch_thing() -> Result<(), ServerFnError> { ... }
// after
#[server(FetchThing, "/api")]
#[cfg_attr(feature = "ssr", server(method = GET))]
async fn fetch_thing() -> Result<(), ServerFnError> { ... }

Defensive patterns

Strategy: validation

Validate before calling

const SUPPORTED: &[&str] = &["GET", "POST", "PUT", "DELETE", "PATCH"];
fn server_fn_method_supported(method: &str) -> bool {
    SUPPORTED.contains(&method.to_uppercase().as_str())
}

Type guard

fn is_supported_method(m: &http::Method) -> bool {
    matches!(m, &http::Method::GET | &http::Method::POST | &http::Method::PUT | &http::Method::DELETE | &http::Method::PATCH)
}

Prevention

Stick to the default POST method or the five supported verbs in #[server] config.
Review generated server-function registrations in CI for non-standard methods.
Add a build-time test that leptos_routes() constructs without panicking for all registered functions.

When it happens

Trigger: Calling LeptosRoutes::leptos_routes/leptos_routes_with_context on an Axum router when a registered server function declares an HTTP method outside the supported set (e.g. via custom #[server] macro configuration setting method to HEAD or OPTIONS).

Common situations: Customizing server function methods with non-standard verbs; hand-written or generated server function registrations with typos in the method; using a macro or codegen that emits methods Axum routing helpers here don't cover.

Related errors

AI-assisted analysis of leptos-rs/leptos@32d20f6c9d (2026-09-01). Data as JSON: /api/errors/a2b9ff1de8b89d09. Report an issue: GitHub.