sondahub

sondahub offers a collection of free fake backend APIs representing multiple industries such as e-commerce, banking, IoT, social media, and healthcare. It supports numerous protocols including REST, GraphQL, gRPC, MQTT, SAML, OAuth, and many others. The service provides realistic API behaviors, persistent writes tied to user sessions without a database, and sandboxes for popular third-party APIs like Stripe, Twilio, and OpenAI. It enables developers to test integrations, authorization flows, and client behaviors without accounts or keys.