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).

Hey Product Hunt 👋 We're the team behind Apinizer (API management). For years, our customers — banks, government agencies, insurers, hospitals, defence — told us the same thing: "When we test our APIs, our data must never leave the machine." But modern API tools keep moving the opposite way. Collections, tokens, request/response bodies increasingly sync to a vendor cloud. For teams in regulated or air-gapped environments, that isn't a feature — it's an unacceptable risk. That was our #1 reason to build this. Two more reasons: these tools keep changing (yesterday's free feature is behind a login/cloud/paywall today), and even the small utilities we open every day — jwt.io, text diff — force us online. So we built Testnizer: 🔒 Fully offline. The UI physically can't reach the internet (CSP connect-src 'self') — every request goes through a local process you control. Collections live in local SQLite on your disk; tokens sit in your OS keychain (Keychain / DPAPI / libsecret). Nothing leaves your machine. 🧰 The tools you use daily, built in and offline. JWT decode/encode, text diff, JSONPath, XPath, XSLT, Jolt, Hash, HMAC, Base64, UUID, Epoch, Regex, JSON↔XML, WS-Security… everything you'd normally paste into jwt.io — now without going online. 🌐 One app, every protocol. REST, SOAP, WebSocket, GraphQL, gRPC, SSE, Socket.IO, MCP. 🔎 Open source (MIT). Don't take our word that your data stays local — read the code. 💻 Free & standalone for Windows, macOS, and Linux. No server, no account, no cloud. We're building in the open and it's still early — if you hit a bug or want a feature, tell us on GitHub issues. Every piece of feedback goes straight into the roadmap. 🙏 Would love to hear what you think! 🌐 https://www.testnizer.com 🐙 https://github.com/apinizer/test...

honestly this is kind of a dream, i hate how postman and insomnia lock features behind accounts. the local sqlite and keychain setup means i can actually version control stuff properly without workarounds.

finally a desktop api client that doesn't nag me to sign up. love that collections live in sqlite and secrets stay in the keychain. one thing i'd really appreciate is a built-in mock server so i can stub responses from my saved collections and let the frontend dev hit them without spinning up anything else.

Testnizer — The offline API client

Offline, open-source API client. Your data never leaves.

Offline, open-source API client. Your data never leaves.