Kasta #

Kasta (Swedish: "to throw") — quickly throw TypeScript programs onto the web.

Kasta is a runtime for hosting small TypeScript programs called kasts. Write a kast, publish it to your AT Protocol PDS, sync it to Kasta, and it becomes a live HTTP endpoint.

How it works #

A kast is a TypeScript file that exports a default HTTP handler:

export default function handler(req: Request): Response {
  return new Response("hello!");
}

Kasta executes each kast in an isolated Deno Worker per request. Any HTTP verb is supported — the full Request is passed to your handler and your Response is returned to the caller.

Each kast gets a URL at:

kasta.app/{your-handle}/{kast-name}

AT Protocol integration #

Kasta uses your AT Protocol PDS as the source of truth for your kasts. No Kasta account needed — your ATP identity is your Kasta identity.

Two record types live in your PDS:

me.wilb.kasta.code — an immutable snapshot of a kast's source code:

{
  "$type": "me.wilb.kasta.code",
  "name": "hello",
  "files": [{ "path": "main.ts", "content": "..." }],
  "entrypoint": "main.ts",
  "lang": "typescript",
  "createdAt": "2026-04-13T00:00:00Z"
}

me.wilb.kasta.pointer — points to the currently active version (rkey = kast name):

{
  "$type": "me.wilb.kasta.pointer",
  "name": "hello",
  "active": {
    "uri": "at://did:plc:.../me.wilb.kasta.code/rkey",
    "cid": "bafy..."
  },
  "updatedAt": "2026-04-13T00:00:00Z"
}

To deploy a new version: write a new me.wilb.kasta.code record, update the me.wilb.kasta.pointer to reference its CID, then call POST /sync.

Deploying a kast #

1. Write an me.wilb.kasta.code record to your PDS
2. Create or update an me.wilb.kasta.pointer record (rkey = kast name) pointing to the code CID
3. Notify Kasta to sync:

curl -X POST https://kasta.app/sync \
  -H "content-type: application/json" \
  -d '{"handle": "you.bsky.social"}'

Kasta will respond with the URLs of all your active kasts.

Running the server #

deno task start

Requires Deno 2.2+. The server starts on port 8000 by default. Set BASE_URL to control the URL prefix returned in sync responses:

BASE_URL=https://kasta.app deno task start

Running tests #

deno task test

API #

File structure #

src/
  server.ts         # Hono app and route wiring
  db.ts             # SQLite schema and queries
  atproto.ts        # AT Protocol handle resolution and PDS record fetching
  sync.ts           # Sync orchestration
  runner.ts         # Deno Worker execution
  worker_harness.ts # Worker script that runs kast code
tests/
  *.test.ts
main.ts             # Entry point