The server could not understand the request — malformed JSON, a missing required field, or a parameter of the wrong type.
The baseline negative test. It is also the code most often used where 422 would be more accurate, so check which one your API actually sends.
101 endpoints in this playground answer with 400. Every one is free, needs no signup, and can be called from the browser or with curl.
GET https://funapi.dev/api/friends/v1/characters — Invalid page parameter, or an unknown query parameter (strict mode) (Friends API)GET https://funapi.dev/api/friends/v1/characters/{id} — Invalid id (Friends API)POST https://funapi.dev/api/friends/v1/characters — Missing name / invalid JSON (Friends API)POST https://funapi.dev/api/friends/v1/characters/bulk — Body is not a JSON array (Friends API)PUT https://funapi.dev/api/friends/v1/characters/{id} — Empty body / invalid JSON (Friends API)POST https://funapi.dev/api/friends/v1/characters/bulk-delete — "ids" is missing, empty, or not an array of integers (Friends API)GET https://funapi.dev/api/friends/v1/episodes — Non-integer season (Friends API)GET https://funapi.dev/api/friends/v1/friends/v2/characters — Invalid page parameter (Friends API)POST https://funapi.dev/api/friends/v1/graphql — Missing "query" string, or completely unrecognized syntax (Friends API)GET https://funapi.dev/api/superheroes/v1/heroes — Invalid page (Superhero API)POST https://funapi.dev/api/superheroes/v1/heroes — Missing name or power (Superhero API)POST https://funapi.dev/api/superheroes/v1/heroes/versus — Same hero twice or unknown id (Superhero API)GET https://funapi.dev/api/pizza/v1/menu — Invalid vegetarian value (Pizza Orders API)POST https://funapi.dev/api/pizza/v1/orders — Unknown pizzaId, bad size, or missing address (Pizza Orders API)PUT https://funapi.dev/api/pizza/v1/orders/{id}/status — Invalid status value (Pizza Orders API)PATCH https://funapi.dev/api/pizza/v1/orders/{id} — Empty body, invalid JSON, or bad size (Pizza Orders API)GET https://funapi.dev/api/coffee/v1/drinks — Invalid type (Coffee Shop API)POST https://funapi.dev/api/coffee/v1/orders — Unknown drinkId or missing name (Coffee Shop API)GET https://funapi.dev/api/football/v1/teams — Invalid page (Football API)POST https://funapi.dev/api/football/v1/matches — Same team twice or unknown team (Football API)GET https://funapi.dev/api/movies/v1/movies — Invalid sort or page, or an unknown query parameter (strict mode) (Movies API)GET https://funapi.dev/api/movies/v1/search/fuzzy — Missing "q" or invalid maxDistance (Movies API)POST https://funapi.dev/api/movies/v1/movies — Missing title (Movies API)PUT https://funapi.dev/api/movies/v1/movies/{id}/rating — Rating outside the inclusive 0–10 range (Movies API)POST https://funapi.dev/api/movies/v1/movies/{id}/poster — Missing filename or sizeBytes (Movies API)…and 76 more endpoints across the catalog.
All HTTP status codes · All 37 mock REST APIs · Getting started guide