Milkman — Privacy-First API Client

Milkman is a privacy-first, open-source desktop API client with zero telemetry, no account requirement, and no cloud dependency — all data stays on your local machine. Postman is a commercially operated product that requires an account, stores collections in the cloud, and collects usage telemetry. Milkman is built in Java and runs on any platform with Java 11+. Postman is Electron-based. Milkman's plugin architecture allows extending it with support for many protocols beyond REST, whereas Postman's extensibility is more limited. The trade-off is that Milkman has a smaller community and fewer built-in integrations than Postman.

Milkman has a rich plugin ecosystem. Core plugins include: REST (HTTP/HTTPS requests), GraphQL, WebSocket, gRPC, SQL (execute queries against databases), JavaScript (run scripts), Git (commit and push from inside Milkman), and Cassandra. Community plugins extend it further. Plugins are JAR files placed in the plugins directory. Each plugin adds a new request type — for example, the WebSocket plugin adds a WebSocket connection tab, the gRPC plugin adds support for protobuf services. This makes Milkman unusually versatile for a desktop API client.

API clients regularly handle sensitive data: production credentials, authentication tokens, API keys, PII in request/response bodies, and internal endpoint URLs. Tools that sync this data to the cloud or collect telemetry create a potential data leakage surface. Regulated industries (healthcare, finance, government) often have policies that prohibit sending API request data to third-party cloud services. Privacy-first tools like Milkman and Bruno store everything locally with no outbound data transmission, making them compliant with strict data handling requirements and eliminating the risk of credentials being exposed via a vendor's cloud infrastructure.

Milkman supports named environments, each containing a set of key-value variable pairs. Switch between environments (development, staging, production) from the environment dropdown. Variables are referenced in request URLs, headers, and body using double-curly brace syntax. Environments are stored as local files and can be imported/exported for sharing with teammates via Git or file share without involving any cloud service. Secret values in environments are masked in the UI to prevent accidental exposure.

Yes, both via plugins. The GraphQL plugin provides a dedicated query editor with schema introspection support — Milkman can fetch the schema from a GraphQL endpoint and display it for reference. The gRPC plugin supports unary, server-streaming, client-streaming, and bidirectional-streaming calls. You provide the .proto file or a reflection-enabled endpoint, define the request message, and execute the call. Both plugins are maintained as part of the Milkman plugin ecosystem and are available in the official releases.

Milkman requires Java 11 or higher. It is distributed as a platform-specific installer for Windows (installer and portable ZIP) and macOS, and as a cross-platform JAR for Linux. On most systems you can check your Java version with java -version. If Java is not installed, adopt OpenJDK from adoptium.net — it is free and open-source. Milkman itself is open-source under the MIT license and available at milkman.dev. It has modest hardware requirements and runs well on older machines.