Open-source Thunder Client alternatives

Hoppscotch is an open-source API development ecosystem for sending requests, inspecting responses and organizing API work. It is positioned as an alternative to Postman and Insomnia and runs in the browser, as a desktop app and from a command line interface, with offline, on-premises and cloud options.

The request builder supports the standard HTTP methods plus custom ones, and the toolset extends to GraphQL and WebSocket testing. You can generate code snippets for more than ten languages and frameworks, share requests through public URLs, and install the web app as a progressive web app for offline use. The interface is lightweight, with light, dark and black themes, a choice of accent colors and a distraction-free Zen mode.

Hoppscotch is MIT licensed and written mainly in TypeScript with Vue. Teams that need to keep API traffic and collections inside their own network can self-host it, while the hosted service at hoppscotch.io suits individuals who just want to start sending requests.

Bruno is an open-source API client and testing environment, described as a lightweight alternative to Postman and Insomnia. It supports REST, GraphQL, gRPC and WebSocket requests, and runs on macOS, Windows and Linux.

Its distinguishing idea is that collections live directly in a folder on your filesystem, saved in a plain text markup language called Bru. That means you can version and share API collections with Git or any version control system you already use. Bruno is offline only, and the maintainers state they have no plans to add cloud sync, because they believe your data should stay on your device. A CLI runs collections from the command line for automated testing and CI/CD, and a Docker option is also documented.

The core is MIT licensed, and the project offers paid versions that add further features for teams that want them. Bruno can be installed from the website or through Homebrew, Chocolatey, Scoop, Snap, Flatpak and Apt. It suits developers who prefer keeping API definitions next to their code.

Insomnia is an API client from Kong that is open source and runs on every major desktop platform. It handles GraphQL, REST, WebSockets, Server-Sent Events, gRPC and other HTTP-compatible protocols, so one desktop app can cover most of the API work a developer does day to day.

With it you can debug requests, design APIs in a native OpenAPI editor with visual preview, test them with native test suites and a collection runner, and mock them with a cloud or self-hosted mock server. A command line tool supports linting and testing in CI/CD pipelines, collaboration features help teams share work, and third-party plugins extend the app. Projects can be stored in a Local Vault for fully local use, synced through any Git repository, or kept in the cloud with optional end-to-end encryption.

Insomnia is Apache-2.0 licensed and written in TypeScript on Electron. It is free to get started with, and paid collaboration features are available from the vendor. It is a popular alternative to Postman for developers who want flexible storage options.

Yaak is a desktop API client for building, sending and inspecting requests to REST, GraphQL, gRPC, WebSocket and Server-Sent Events endpoints. It is built with Tauri, Rust and React and works offline-first, with no telemetry and no requirement to sync data to a cloud account.

Collections from Postman, Insomnia, OpenAPI, Swagger or curl can be imported. Responses can be filtered with JSONPath or XPath, and authentication supports OAuth 2.0, JWT and Basic Auth, with encrypted secrets that can be kept in the operating system keychain. Requests are grouped into workspaces and nested folders, and environment variables switch between dev, staging and production.

Workspaces can be mirrored to the filesystem so they can be versioned in Git or synced with a file-sync service. Template tags insert dynamic values such as UUIDs or timestamps, and themes and plugins allow customization. Yaak is MIT licensed, its repository topics position it as an alternative to Postman, Bruno and Insomnia, and development is funded by community-purchased licenses.

ATAC, short for Arguably a Terminal API Client, is a text user interface for building and sending API requests, similar in spirit to Postman, Insomnia and Bruno but running entirely in your terminal. No graphical environment is needed, which makes it handy over SSH and for keyboard-focused developers.

It is written in Rust using the ratatui library and offers Vim key-bindings, NeoVim integration and themes. The README covers several installation routes, including cargo, Homebrew, Scoop, Arch Linux, Fedora Copr, a Docker package, prebuilt binaries and compiling from source, and it documents features, planned work for the 1.0 and 2.0 releases, and the binary size and dependencies.

ATAC is MIT-licensed and runs locally on your machine, with no account or hosted service required. It suits developers who like terminal workflows and want a lightweight alternative to graphical API clients.

API Dash is an open-source API client for desktop and mobile, built with Flutter and described as a lightweight alternative to Postman and Insomnia. You can create and customize HTTP and GraphQL requests, visually inspect the responses, and generate code for integrating an API into your application. It is released under the Apache-2.0 license and includes AI-assisted features.

Requests can be built with different HTTP methods, headers, query parameters, and bodies, and the app handles Unicode and emoji content in both requests and previews. Requests are organized into collections and folders that you can rearrange, rename, and duplicate. Collections can be imported from Postman, cURL, Insomnia, OpenAPI, and HAR files, and the topics also mention server-sent events and WebSocket support.

Builds are provided for iOS, macOS, Windows, and Linux in several package formats. It suits developers who want a free, native-feeling alternative for exploring and testing APIs and who may want to contribute, since the project takes part in open-source programs and welcomes contributors.

Restfox is a lightweight API testing client for HTTP and socket connections that works offline-first. It is offered as a web app and as desktop builds, and it aims to be a simpler alternative to larger tools such as Postman. It is written in Vue and released under the MIT license.

You send REST requests, work with GraphQL and WebSocket connections, keep a history of responses, define environment variables, and extend the client with plugins. Because it is offline-first, collections are stored locally, and the app can be installed as a PWA from the browser.

Installation options include Homebrew on macOS, Snap on Ubuntu and other distributions, RPM and DEB packages, precompiled binaries for Windows, and Docker Compose for hosting the web app yourself, with an option to change the port. It suits developers who want a quick, privacy-friendly client without accounts or cloud syncing.

Resterm is an API-as-code workbench for the terminal. Requests are saved in plain .http and .rest files that can live in your repository next to code, and the same files can be run in a terminal UI or in CI with a resterm run command. It is written in Go and released under the Apache-2.0 license.

It supports HTTP, GraphQL, gRPC, WebSocket, and server-sent events. Assertions, captures, loops, conditions, and multi-step workflows are written directly in request files, and scripting is available with RestermScript, a small expression language, or JavaScript. Mock servers and traffic recording use the same file format, and the tool handles OAuth 2.0, tokens from CLIs like gh, SSH tunnels, and Kubernetes port-forwards. Tracing, profiling, and OpenAPI import are also included.

Because requests are plain text, they diff and version well in Git. Resterm suits developers who prefer terminal workflows and want API tests that run identically on a laptop and in a pipeline.

Voiden is an offline API client for developers, QA engineers, and technical writers to build, test, collaborate on, and document APIs in one place. APIs are described in plain-text .void files that you keep in Git, with no account and no required cloud sync. It is built with Electron and TypeScript and released under the Apache-2.0 license.

Requests are composed from reusable API blocks that can be replaced and versioned like code, with a slash-command interface and a command-line tool designed to work with AI agents. It supports REST, GraphQL, gRPC, and WebSocket protocols, imports OpenAPI, and topics mention an MCP client. The project says it has no telemetry, no venture funding, and no cloud lock-in.

Voiden is positioned as an alternative to Postman, Bruno, and Insomnia. It suits teams who want their API collections and documentation to live in the repository as files that can be reviewed and shared through normal Git workflows.

Chapar is a native API testing tool for developers, written in Go and designed to start quickly and stay light. It draws its interface with a GPU-rendered UI toolkit rather than a browser engine, and runs the same on macOS, Linux and Windows. Requests, environments and cookies are plain files on your machine, with no account and no cloud sync.

It supports several protocols. For REST and HTTP it handles every method, query and path parameters and JSON, XML, text, form-data, URL-encoded and binary bodies with syntax highlighting. For gRPC it supports server reflection or proto files, unary and server-streaming methods, metadata and trailers, and TLS with client certificates. GraphQL queries and variables are supported with response data and errors shown separately. Workspaces keep separate collections, requests and environments, and a free hosted mock server is available for trying features. WebSocket and MQTT are planned.

Chapar is licensed under BSD-3-Clause and named after the royal mounted couriers of ancient Persia. It is aimed at developers who want a lightweight, privacy-respecting alternative to heavier API clients.