Best Free API Testing Tools Compared: Hoppscotch vs Thunder Client vs REST Client

A backend developer’s browser tab count tells a story. Somewhere between the local docs, the staging dashboard, and three Stack Overflow threads, there’s usually an API client open. For years, Postman was the default answer. But its growing feature bloat, account requirements, and cloud sync prompts have pushed plenty of developers toward lighter alternatives—three of which come up constantly in discussion threads: Hoppscotch, Thunder Client, and REST Client.

They look similar on the surface (all free, all fast, all handle HTTP requests), but they’re built on different philosophies. One is a full web app, one is a VS Code extension with a GUI, and one is a plain-text file format. Here’s how they actually compare in daily use.

The Contenders at a Glance

Hoppscotch Thunder Client REST Client
Type Web app / PWA (self-hostable) VS Code extension VS Code extension
Interface Full GUI, browser-based GUI inside VS Code Plain .http/.rest text files
Price Free tier; paid cloud plans Free tier; paid “Ultimate” license Completely free
Open source Yes (core) No Yes
Account required No (local mode) No No
Best for Quick requests, team sharing Developers who live in VS Code Version-controlled API collections

Hoppscotch: The Browser-First Client

Hoppscotch (formerly Postwoman) started as an open-source answer to Postman and has grown into a polished web app. You open a tab, type a URL, hit send, and you’re done—no install, no login. It supports REST, GraphQL, WebSocket, SSE, and MQTT, which makes it unusually versatile for a free tool.

The interface is fast. Requests fire from your browser, and the response panel handles JSON formatting, headers, and status codes cleanly. Collections, environments, and history are all available in local mode, stored in your browser’s storage.

Where it shines:

  • Zero friction. No install, works on any machine, including locked-down corporate laptops.
  • Self-hostable. Because the core is open source, teams can run their own instance and keep API keys off third-party servers—a real consideration for regulated industries.
  • Multi-protocol support. GraphQL and WebSocket testing in the same free tool is genuinely useful.
  • Installable PWA. You can “install” it like a desktop app without downloading an installer.

Where it stumbles:

  • Browser storage is fragile. Clearing site data wipes your collections unless you’ve synced to an account. That’s a real risk for anyone who treats it as their primary client.
  • Collaboration sits behind the paid tier. The free plan is generous for individuals, but team workspaces and shared collections push you toward Hoppscotch Cloud or a self-hosted deployment.

Hoppscotch is the best choice when you need to test something right now on a machine that isn’t yours, or when you want an open-source client you can host yourself.

Thunder Client: The VS Code Native

Thunder Client is a VS Code extension that puts a Postman-style GUI in your sidebar. The pitch is simple: you’re already in VS Code writing the code that calls the API, so why switch windows?

That proximity is the whole value proposition, and it delivers. You can fire a request, see the response, and edit the handler in the same window. Collections live in your workspace, environments are easy to switch, and the extension supports GraphQL, scripting, and test assertions in its free tier.

Where it shines:

  • Context switching disappears. Debugging a request and fixing the code that sends it happen in one place.
  • Local-first storage. Collections are stored locally by default, with optional git sync—no account required.
  • Scripting and tests. Pre-request and post-response scripts, plus basic assertions, are available without paying.
  • Fast. Lighter than running a full Electron app alongside your editor.

Where it stumbles:

  • It’s not open source. Thunder Client is proprietary. The free tier is genuinely usable, but advanced features (like CLI runs for CI and some team features) sit behind the paid Ultimate license.
  • VS Code lock-in. If you switch editors or need to test from a terminal, you lose your setup.
  • GUI-only workflow. Collections are stored in the extension’s own format, which makes reviewing API changes in pull requests awkward.

Thunder Client is the pragmatic pick for developers who spend most of their day in VS Code and want API testing without another window.

REST Client: The Plain-Text Purist

REST Client (the popular VS Code extension by Huachao Mao) takes the opposite approach: there’s no GUI to speak of. You write requests in a .http or .rest file, and a small “Send Request” link appears above each one. Click it, and the response opens in a side pane.

A request looks like this:

GET https://api.example.com/users/42
Authorization: Bearer {{token}}
Accept: application/json

That’s it. Variables, multiple requests per file, and even response handling via request scripts are supported, but everything lives in text.

Where it shines:

  • Version control native. Your API collection is a text file in your repo. Diffs are readable, pull requests show API changes, and onboarding is just “open this file.”
  • Completely free and open source. No tiers, no upsells, no license keys.
  • Extensible. Supports variables, environments via .env files, request chaining, and even GraphQL and gRPC in recent versions.
  • No vendor lock-in. The format is portable and human-readable; you can commit it, share it, or grep it.

Where it stumbles:

  • No visual collection browser. Large API suites become a scrolling exercise in text files.
  • Learning curve for scripting. Response handling exists but is less discoverable than a GUI’s test tab.
  • Not great for exploratory testing. If you want to poke at an unfamiliar API with a form-based interface, this isn’t it.

REST Client is the choice for teams that treat API definitions as code and want them living next to the source.

Head-to-Head: Which Should You Pick?

The honest answer is that these tools optimize for different things, and plenty of developers use more than one.

Choose Hoppscotch if:

  • You need a client on a machine where you can’t install software
  • You want an open-source, self-hostable option for security reasons
  • You test GraphQL, WebSockets, or MQTT alongside REST
  • You value a clean GUI over deep editor integration

Choose Thunder Client if:

  • VS Code is your primary environment
  • You want a GUI with collections, environments, and scripting without leaving the editor
  • You’re comfortable with a proprietary tool’s free tier

Choose REST Client if:

  • You want API requests versioned in git alongside your code
  • You prefer plain text and zero lock-in
  • You’re willing to trade GUI convenience for portability and openness

A common pattern: use REST Client for the requests that belong in the repo (smoke tests, documented endpoints), and keep Hoppscotch or Thunder Client open for exploratory poking. The tools aren’t mutually exclusive, and none of them requires a credit card.

The Bottom Line

All three tools are legitimately free and genuinely capable—none is a crippled trial. The deciding factor isn’t features so much as where you want your API requests to live. Hoppscotch keeps them in the browser and on your own server if you want. Thunder Client keeps them in your editor. REST Client keeps them in your repository as plain text.

If you’re still defaulting to Postman out of habit, any of these will cover the vast majority of day-to-day API testing without the account prompts. Pick the one whose storage model matches how your team already works, and you’ll spend less time managing the tool and more time shipping the API.