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Testnizer — The offline API client
Offline, open-source API client. Your data never leaves.
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...
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About Testnizer — The offline API client on Product Hunt
“Offline, open-source API client. Your data never leaves.”
Testnizer — The offline API client was submitted on Product Hunt and earned 0 upvotes and 1 comments, placing #16 on the daily leaderboard. 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).
Testnizer — The offline API client was featured in API (98.4k followers), Open Source (68.6k followers), Developer Tools (516.2k followers) and GitHub (41.3k followers) on Product Hunt. Together, these topics include over 126.7k products, making this a competitive space to launch in.
Who hunted Testnizer — The offline API client?
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