Castra

A self-hosted backend on Cloudflare: one Worker and one D1 database in your account serve REST endpoints for your tables. Every endpoint is protected by policies written in TypeScript and compiled to SQL. An MCP server lets AI agents inspect exactly what production enforces.

• Closed by default. A table without a policy has no routes.
• Policies are SQL. Rules become WHERE clauses, so pagination and counts stay correct.
• Checked writes. Every create and update is verified on the stored row, atomically.
• Auth included. Better Auth (email, GitHub), roles and API keys.
• Agent-safe MCP. Read and write tools on the same engine and write path as REST, with scoped tokens and an audit log.

Status: v0.4.1 (changelog). Early, but deployed and working. Upgrading from 0.4.0? See the upgrade guide. Read Status and limits before using it for anything important.

Quick start

Requires Node 20+ and pnpm.

npm create @castra-kit@latest my-app
cd my-app
cp .dev.vars.example .dev.vars    # set BETTER_AUTH_SECRET: openssl rand -base64 32
pnpm db:migrate:local
pnpm dev                          # http://localhost:8787/health

Deploy to your Cloudflare account (token permissions: docs/cloudflare-token.md):

CLOUDFLARE_API_TOKEN=... pnpm run deploy

The full walkthrough, including your first request and your first policy, is in Getting started.

What a policy looks like

import { authenticated, defineConfig, isPublic, owner, role } from "@castra-kit/core";

export default defineConfig({
  database: "d1",
  roles: ["admin", "editor"],
  tables: {
    posts: {
      read: isPublic().where((q) => q.eb("status", "=", "published")).or(owner("author_id")),
      create: authenticated(),
      update: owner("author_id").or(role("editor", "admin")),
      delete: role("admin"),
      fields: { author_id: { setBy: "server" } },
    },
  },
});
// Any table not listed here is never exposed.

Documentation

Getting started	Scaffold, run, first request, first policy, deploy
Concepts and configuration	Rules, write checks, field rules, config reference
REST API	Routes, filters, sorting, pagination, includes, errors
Auth	Better Auth, sessions, roles, API keys
MCP	Tools, local stdio server, remote /mcp, tokens and scopes
CLI	castra generate, provision, migrate, deploy, doctor, mcp
Rate limiting	Per-IP write limits, WAF rule for reads
Status and limits	What is verified, D1 limits, what is out of scope
Security	Threat model, guarantees, known issues
Problem types	Every error code the API returns
Architecture ·

Questions and ideas: Discussions. Troubleshooting and FAQ: Wiki.

Packages

Package
@castra-kit/core	Policy engine, schema snapshot, REST router, OpenAPI
@castra-kit/auth	Better Auth wiring, roles, API keys
@castra-kit/mcp	MCP tools, stdio server, /mcp route
@castra-kit/app	createCastraApp: the Worker wiring in one call
@castra-kit/cli	The castra command
@castra-kit/create	Project scaffolder

Contributing

See CONTRIBUTING.md. Report vulnerabilities privately, as described in SECURITY.md.

License

MIT © Mehmet Özer Özdaş