Freedom251 › Web Debugging Proxies
Mediator
What Mediator is
Mediator is a free, open-source desktop proxy for debugging gRPC traffic on Linux, macOS, and Windows. Developers can redirect requests to beta or test servers without changing client code. When an API schema is available, Mediator parses gRPC requests and responses and can show binary messages as a JSON tree. Schemas can come from server reflection, proto source roots compiled with protoc, or FileDescriptorSet files. For matching server rules, it can decode gRPC and HTTPS requests 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. Desktop downloads include Windows MSI, macOS DMG, Apple Silicon macOS DMG, and Linux deb packages. The project also gives proxy setup examples for Java, Objective-C/iOS, and Go clients. Mediator is licensed under Apache-2.0.
Who it suits
Mediator suits developers configuring gRPC clients who need to redirect or inspect traffic across desktop operating systems. It is useful when an API schema is available for decoding messages.
What it does well
- Redirects traffic without client-code changes.
- Parses messages when an API schema is available.
- Supports three schema-source types.
- Downloads are listed for Windows, macOS, and Linux.
- Free under Apache-2.0.
What to know first
- HTTPS inspection requires installing the generated root certificate.
- A different installation requires reinstalling its certificate.
- Message decoding depends on an available API schema.
Limits
Parsing gRPC messages and displaying binary messages as a JSON tree require an API schema. HTTPS decoding requires a matching server rule and the client certificate from the same installation.
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| Free | Cross-platform GUI gRPC debugging proxy · Apache-2.0 licensed | Free |
As github.com lists them, read 4 Oct 2026. The maker's own page has the final word.
Getting started
- Download the Windows MSI, macOS DMG, Apple Silicon macOS DMG, or Linux deb package.
- Install and open Mediator; its proxy listens on port 8888 by default.
- Configure the gRPC client to use the proxy, following the project examples for Java, Objective-C/iOS, or Go.
- Provide a schema through server reflection, compiled proto source roots, or a FileDescriptorSet file when message parsing is needed.
- For HTTPS decoding, install the root certificate generated by that Mediator installation in the client.
- Add a matching server rule for requests to decode.
Verdict
Mediator provides a free desktop proxy with schema-based gRPC message decoding and request redirection. Certificate setup is required for matching HTTPS inspection, and certificates are specific to each installation.
Questions
Is Mediator free?
Yes. The project lists a free plan at no cost, and identifies the software as open source under Apache-2.0.
Which operating systems does it support?
Mediator supports Linux, macOS, and Windows. The project lists deb, DMG, Apple Silicon DMG, and MSI downloads.
Does Mediator need a schema to parse messages?
Yes. An API schema is needed to parse gRPC messages and render binary messages as a JSON tree. Supported sources include server reflection, proto source roots compiled with protoc, and FileDescriptorSet files.
How does HTTPS decoding work?
It works when a server rule matches and the client has installed the root certificate generated by that Mediator installation. Certificates are available in DER and PEM formats.
What is the default proxy port?
When the app opens, its proxy server listens on port 8888 by default.
Which client setup examples are provided?
The project README gives proxy setup examples for Java, Objective-C/iOS, and Go clients.
Facts from Mediator's own pages
- Certificate handling
- Each installation generates its own root certificate, available in DER and PEM formats, and a different installation requires reinstalling its certificate. · github.com, 4 Oct 2026
- Client examples
- The README gives proxy setup examples for Java, Objective-C/iOS, and Go clients. · github.com, 4 Oct 2026
- Desktop downloads
- The project lists Windows MSI, macOS DMG, Apple Silicon macOS DMG, and Linux deb distributions. · github.com, 4 Oct 2026
- Desktop framework
- The project says it uses Netty for the proxy protocol, Compose Desktop for the GUI, and Sisyphus as the Protobuf runtime. · github.com, 4 Oct 2026
- Host rewrite
- It can redirect requests to beta or test servers without changing client code. · github.com, 4 Oct 2026
- HTTPS inspection
- It can decode gRPC/HTTPS requests when a server rule matches, using a Mediator root certificate installed in the client. · github.com, 4 Oct 2026
- Intended users
- The repository describes the product as a gRPC debugging proxy and provides setup instructions for developers configuring gRPC clients. · github.com, 4 Oct 2026
- License
- The repository identifies its license as Apache-2.0. · github.com, 4 Oct 2026
- Protobuf decoding
- It parses gRPC request and response messages and can render binary messages as a JSON tree when an API schema is available. · github.com, 4 Oct 2026
- Proxy default
- When the app opens, its proxy server listens on port 8888 by default. · github.com, 4 Oct 2026
- Purpose
- Mediator is a cross-platform GUI proxy for debugging gRPC traffic. · github.com, 4 Oct 2026
- Schema sources
- Mediator supports gRPC server reflection, proto source roots compiled with protoc, and FileDescriptorSet files as API schema sources. · github.com, 4 Oct 2026
Where Mediator stands on Freedom251
- Web Debugging Proxies#6 of 27
- gRPC Tools#18 of 24