Cessy Builder Docs

Cessy is a builder platform for configurable event-sourced business apps. You model the business once, publish it, and Cessy materializes the runtime surfaces: command APIs, projection reads, webhooks, subscriptions, MCP tools, channels, and custom pages.

These docs are written for human builders. If you are using an AI coding agent, connect it to the Design MCP early; the Design MCP exposes the current app model, reference knowledge, validation tools, workspace changesets, and page preview tools.

First path

  1. Read Builder Journey for the end-to-end mental model.
  2. Connect Claude, Codex, or another MCP client through Connect Design MCP.
  3. Run the Quickstart against a real app.
  4. Use DomainConfig when you need to understand the generated model.
  5. Use Runtime API when you need to integrate an external system.

Builder surfaces

SurfaceUse it for
Builder UIModel decisions, commands, events, projections, policies, permissions, agents, adapters, credentials, pages, and publishing.
Design MCPLet Claude, Codex, ChatGPT, or ces inspect and change app design with validation and reference context.
Runtime APILet external systems execute published commands and read published projections.
Runtime MCPLet app agents operate the published app through generated tools.
Custom pagesBuild app-specific screens on top of published runtime contracts.

Core rule

Business behavior belongs in the event-sourced model. Frontends, agents, webhooks, adapters, and external clients should call the generated runtime surfaces instead of reimplementing business rules.