Testnizer — The offline API client

What it does

A free, standalone desktop API client (REST, SOAP, GraphQL, gRPC, WebSocket & more) that runs 100% offline. Collections stay in local SQLite, tokens in your OS keychain — nothing ever goes to a vendor cloud. Built-in offline dev tools. Open source (MIT).

The offline API client for teams requiring absolute data privacy. Free, fully offline desktop API testing for banking, government, healthcare, defence.

Test HTTP, SOAP, WebSocket, GraphQL, gRPC and SSE — then sign a JWT, open a JKS keystore, build a SAML assertion or inspect a live TLS chain without leaving the app, and without a key or a token ever being uploaded anywhere. Free, and built by Apinizer for teams in banking, government, insurance and healthcare where production credentials and payloads must never leave the machine. The cryptography runs where the app runs: keystores (JKS / PKCS#12, no keytool), certificates and mTLS , JWT / JOSE , JWK / JWKS , WS-Security , SAML and live TLS inspection — with the private key never leaving the app core. See the toolbox → Imported a Swagger spec, ran a POST, got a 200. No account, no cloud…from testnizer.com

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