Explore and call your APIs with code

A code-based UI for exploring and calling gRPC and Twirp APIs.
Write TypeScript to construct requests, call services, and inspect responses — no forms, no clicking through fields.

 

Live Demo · Website

Features

• Code-based — Write TypeScript to call your APIs. Full autocomplete for services, methods, and message fields.
• gRPC & Twirp — Native support for both protocols. Reads your .proto files or uses gRPC server reflection.
• macOS & Docker — Available on the Mac App Store or as a Docker container for any environment.

Run with Docker

docker run --pull always --name kaja -d -p 41520:41520 \
    -v /my_app/proto:/workspace/proto \
    -v /my_app/kaja.json:/workspace/kaja.json \
    --add-host=host.docker.internal:host-gateway kajatools/kaja:latest

Then open http://localhost:41520.

Configuration

On macOS, apps are configured through the UI. The configuration is stored at ~/Library/Application Support/kaja/kaja.json.

With Docker, create a kaja.json file and mount it into the container. Every entry in apps is one app: a name plus one block whose key is the app's type, holding that type's parameters:

{
  "apps": [
    {
      "name": "users",
      "twirp": {
        "url": "http://host.docker.internal:41522",
        "proto_dir": "users/proto"
      }
    },
    {
      "name": "teams",
      "grpc": {
        "url": "host.docker.internal:41523",
        "reflection": true,
        "headers": { "Authorization": "Bearer xxx" }
      }
    }
  ]
}

App options

Each app has a name and exactly one typed block:

Type	Parameters
grpc	url, proto_dir (path to .proto files), reflection (use gRPC server reflection instead of local proto files), headers
twirp	url, proto_dir, headers

headers are sent with each request (e.g. {"Authorization": "Bearer xxx"}); for gRPC they are sent as metadata.

Migrating from the old format

Earlier versions used a top-level projects list with a protocol field. Kaja migrates these automatically on load — but to update a file by hand, move each project into apps and replace its protocol/url/protoDir/useReflection fields with a block named after the type.

Before:

{
  "projects": [
    { "name": "users", "protocol": "RPC_PROTOCOL_TWIRP", "url": "http://host.docker.internal:41522", "protoDir": "users/proto" }
  ]
}

After:

{
  "apps": [
    { "name": "users", "twirp": { "url": "http://host.docker.internal:41522", "proto_dir": "users/proto" } }
  ]
}

Docker arguments

Argument	Description
--pull always	Always pull the latest image. Kaja is updated frequently.
--name kaja	Name the container for easy management.
-d	Run in detached mode.
-p 41520:41520	Map the container port. Kaja listens on 41520 by default.
-v .../proto:/workspace/proto	Mount your proto_path into the container.
-v .../kaja.json:/workspace/kaja.json	Mount your configuration file.
--add-host=host.docker.internal:host-gateway	Access host services from the container.

Development

The development scripts require Go and Bun installed. If not installed, they will offer to install them for you via Homebrew.

• Run in local server: scripts/server
• Run in Docker: scripts/docker
• Run the desktop app: scripts/desktop
• Test UI: (cd ui && bun test)
• TSC UI: (cd ui && bun run tsc)
• Test server: (cd server && go test ./... -v)
• Update demo protos: scripts/demo-protos (The demo services are deployed via kaja/tools/website)