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Mediator

github.com

Free plan WindowsmacOSLinux
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Spec score 7.7 #20 of 27 in Web Debugging Proxies

What it is

Mediator is a free, open-source desktop proxy for debugging gRPC traffic on Linux, macOS and Windows. It can redirect requests to beta or test servers without changes to client code. When an API schema is available, it parses gRPC requests and responses and presents binary messages as a JSON tree. Schemas can come from server reflection, proto source roots compiled with protoc, or FileDescriptorSet files. Matching server rules also allow gRPC and HTTPS decoding after the client installs the root certificate generated by that Mediator installation. Certificates are available in DER and PEM formats, and another installation requires its own certificate. The proxy listens on port 8888 by default. Downloads include Windows MSI, macOS DMG, Apple Silicon macOS DMG and Linux deb packages. Setup examples cover Java, Objective-C/iOS and Go clients. The repository identifies Apache-2.0 as its license.

Spec sheet

Purpose
Mediator is a cross-platform GUI proxy for debugging gRPC traffic.Read 4 Oct 2026 · github.com
Intended users
The repository describes the product as a gRPC debugging proxy and provides setup instructions for developers configuring gRPC clients.Read 4 Oct 2026 · github.com
License
The repository identifies its license as Apache-2.0.Read 4 Oct 2026 · github.com
Certificate handling
Each installation generates its own root certificate, available in DER and PEM formats, and a different installation requires reinstalling its certificate.Read 4 Oct 2026 · github.com
Client examples
The README gives proxy setup examples for Java, Objective-C/iOS, and Go clients.Read 4 Oct 2026 · github.com
Desktop downloads
The project lists Windows MSI, macOS DMG, Apple Silicon macOS DMG, and Linux deb distributions.Read 4 Oct 2026 · github.com
Desktop framework
The project says it uses Netty for the proxy protocol, Compose Desktop for the GUI, and Sisyphus as the Protobuf runtime.Read 4 Oct 2026 · github.com
Host rewrite
It can redirect requests to beta or test servers without changing client code.Read 4 Oct 2026 · github.com
HTTPS inspection
It can decode gRPC/HTTPS requests when a server rule matches, using a Mediator root certificate installed in the client.Read 4 Oct 2026 · github.com
Protobuf decoding
It parses gRPC request and response messages and can render binary messages as a JSON tree when an API schema is available.Read 4 Oct 2026 · github.com
Proxy default
When the app opens, its proxy server listens on port 8888 by default.Read 4 Oct 2026 · github.com
Schema sources
Mediator supports gRPC server reflection, proto source roots compiled with protoc, and FileDescriptorSet files as API schema sources.Read 4 Oct 2026 · github.com

Plans and prices

Free Free Cross-platform GUI gRPC debugging proxy · Apache-2.0 licensed Read 4 Oct 2026 · github.com

Every Mediator plan and price →

Strong points and limits

Strong points

  • Free and Apache-2.0 licensed
  • Runs on Linux, macOS and Windows
  • Schema-aware JSON message views
  • Redirects traffic without client-code changes
  • Desktop packages for major platforms

Limits

  • Requires an installed root certificate for HTTPS decoding
  • Certificates differ between installations
  • Proxy defaults to port 8888

Who it suits

Mediator is aimed at developers configuring gRPC clients and inspecting traffic across desktop operating systems. It suits teams needing schema-aware message views or test-server redirection.

Verdict

Mediator provides a cross-platform GUI for routing and examining gRPC traffic. Its certificate setup and dependence on available API schemas are important parts of deployment.

Where Specifiction places it

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