Sanjeev Kumar

Posted on May 15

I built a free, local-first Postman alternative — no account, no cloud, no subscription

#api #testing #webdev #opensource

I got tired of Postman.

Not the tool itself — Postman is genuinely good. What I got tired of was the friction: the mandatory account, the cloud sync I didn't ask for, the features hidden behind a $12/month plan, the loading screen every time I just wanted to hit an endpoint. And when Postman announced that the free plan would be limited to a single user starting March 2026, a lot of teams started asking the same question: what else is out there?

So I built API Sentinel — a free, local-first desktop API client. No account. No cloud. No subscription. Everything runs on your machine.

Download: github.com/Sanjeevsky/api-sentinel-downloads
Landing page: sanjeevsky.github.io/api-sentinel-downloads

Why local-first matters

Most API clients have drifted toward cloud-first architectures. That means your collections, environments, request history, API keys, and internal endpoint URLs are sitting on someone else's server. For teams working on internal APIs, financial systems, or anything with compliance requirements — that's a problem.

API Sentinel takes the opposite approach:

No account required — launch and start testing immediately
No cloud sync — everything is stored on your filesystem
No telemetry by default — nothing phones home unless you enable it
Works fully offline — no internet needed to use the app itself

Your request data, API credentials, and collections never leave your machine.

What's included — everything, free

This is the part where most tools have an asterisk. API Sentinel doesn't. Every feature is in the free download:

Request building

URL bar with autocomplete and direct cURL import
All HTTP methods, HTTP/1.1 and HTTP/2
Structured editors for params, headers, auth (Bearer, Basic, API Key, OAuth), cookies, variables
Body modes: JSON, raw, form-data, urlencoded, GraphQL, binary file uploads
Pre-request and test scripting with assertions
Code generation from any request

Response analysis

Pretty-print, raw, and JSON tree views
Headers, cookies, timing, and timeline data
Response search and export
Markdown and schema-style rendering

Regression testing

Save response snapshots locally
Mark baselines and compare current vs saved
Side-by-side diff between any two responses
All snapshots stay on your machine

Organization

Collections with nested folders and environments
Multiple environments (local, staging, prod) with variable toggles
Full request history with time machine inspection
Import: cURL, OpenAPI/Swagger, HAR, common API client formats

Automation and flows

Collection runner — execute multiple requests in sequence with pass/fail reporting
Scheduled runs — recurring local automation, results stored locally
Flows — chain requests where one uses another's output (login → fetch profile → validate)
Proxy capture — intercept real network traffic and build requests from it

Protocol support

REST and HTTP (all methods)
GraphQL — schema introspection, query editor, mutations, subscriptions
WebSocket — full composer with message history
SSE — Server-Sent Events client
Socket.IO — dedicated composer
MQTT — client with topic subscriptions

Testing and security

Mock server — local endpoint simulation, no external service needed
Load testing — concurrent virtual users, duration-based runs, latency/throughput metrics
Security testing — passive scan helpers, fuzzing passes, common API vulnerability checks
Everything runs locally — no data sent externally

How it compares to Postman and Insomnia

Feature	API Sentinel	Postman	Insomnia
Mock server	✅ Free	Paid plan	Limited
Load testing	✅ Free	Paid plan	✗
Security testing	✅ Free	Paid plan	✗
Collection runner	✅ Free	Limited free	Limited
Scheduled runs	✅ Free	Paid plan	✗
Chained flows	✅ Free	Paid plan	✗
WebSocket	✅ Free	✅ Free	Limited
SSE client	✅ Free	Partial	✗
Socket.IO	✅ Free	✗	✗
MQTT	✅ Free	✗	✗
Proxy capture	✅ Free	Limited	✗
Snapshot regression	✅ Free	Paid plan	✗
AI assistant	✅ Free	Paid plan	✗
No account required	✅	✗	✗
Local-first storage	✅	✗ Cloud	Partial
Works offline	✅	Partial	Partial
Price	Free	Freemium / $12+/mo	Freemium / $8+/mo

Everything Postman puts behind a paid plan is free in API Sentinel, and your data never leaves your machine.

Screenshots

Main workspace — REST testing, response inspection, history:

Request composer with cURL import:

Response viewer with JSON tree and snapshot comparison:

Mock server for local endpoint simulation:

Platform support

Windows — .exe for x64
macOS — .dmg for Intel and Apple Silicon
Linux — .deb for x64

Current version: v0.0.1 — initial public release.

macOS note: Current builds are preview releases and not yet notarized by Apple. On first launch: right-click → Open → approve in System Settings → Privacy & Security → Open Anyway. Full notarization is on the roadmap.

Why I built this instead of Bruno or Insomnia

Bruno is excellent for Git-native, file-based collections — but no built-in mock server, load testing, or real-time protocol support. You'd need separate tools for those.

Insomnia is solid for daily REST and GraphQL work but has drifted toward cloud and freemium. No load testing, no scheduled runs, no chained flows, no MQTT or Socket.IO.

Hoppscotch is great for quick browser-based checks but not a full desktop client, and doesn't run fully offline.

API Sentinel is the tool I wanted to exist: everything in one place, all local, all free, no account.

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