fractal

Define your API as plain functions, project it to any protocol surface.

https://docs.rhi.zone/fractal/

The composition unit is Node<P,Res> = { meta, handler }. meta is the reflection descriptor — walkable, serialisable — built during route construction. handler is the executable. Transports, validation, and static types are opt-in layers composed via combinators; they are not in the core.

Write the tree once. Multiple interpreters walk it to produce an HTTP server with OpenAPI, a GraphQL server with SDL, an MCP server (tools/resources/prompts/sampling), a CLI, and type-safe clients for each — all from the same definition.

Packages

Package	Role
@rhi-zone/fractal	Umbrella — the core on the package root, one subpath per protocol (/http, /cli, /json-rpc, /graphql, /mcp). Start here if you want more than one protocol
@rhi-zone/fractal-api-tree	Core: api/op tree constructors, Node/Handler/Meta, the tag lattice, source-level schema extraction
@rhi-zone/fractal-type-ir	Type IR — subtyping hierarchy + open metadata bag, projectable to 20+ targets (JSON Schema, OpenAPI, GraphQL SDL, SQL DDL, Protobuf, Zod, ...)
@rhi-zone/fractal-http-api-projector	HTTP projection — compiled router, OpenAPI 3.1, typed client
@rhi-zone/fractal-http-framework-projector	Router codegen for existing HTTP frameworks (Express, more to follow) — eject model, not a runtime
@rhi-zone/fractal-graphql-api-projector	GraphQL projection — SDL, resolver dispatch, subscriptions, typed client
@rhi-zone/fractal-mcp-api-projector	MCP projection — tools, resources, prompts, sampling
@rhi-zone/fractal-cli-api-projector	CLI projection — subcommand dispatch, shell completions, streaming
@rhi-zone/fractal-json-rpc-api-projector	JSON-RPC 2.0 projection — HTTP POST + WebSocket transports, batch requests, typed client

Each projector is installable on its own; bun add @rhi-zone/fractal gets the core plus HTTP, CLI, and JSON-RPC behind subpaths, with GraphQL and MCP as optional peers so neither protocol's runtime is loaded — or, for the MCP SDK, even installed — by a consumer that doesn't ask for it.

Quick example

Author once:

import { api, op } from "@rhi-zone/fractal-api-tree";
import { http } from "@rhi-zone/fractal-http-api-projector/verbs";

const tree = api({
  books: api({
    list: op(() => [...store.values()], http.get),
    add: op((input: { title: string; author: string }) => addBook(input), http.post),
  }),
});

Project to HTTP, with OpenAPI served for free:

import { createFetch } from "@rhi-zone/fractal-http-api-projector/presets";

const fetch = createFetch(tree);
await fetch(new Request("http://localhost/books/list"));

Project the same tree to MCP tools:

import { toTools } from "@rhi-zone/fractal-mcp-api-projector";

const tools = toTools(tree); // [{ name: "books_list", ... }, { name: "books_add", ... }]

...or to a CLI:

import { runCli } from "@rhi-zone/fractal-cli-api-projector";

await runCli(tree, ["books", "add", "--title", "Dune", "--author", "Herbert"]);

...or to GraphQL SDL and a resolver map — see packages/graphql-api-projector.

Development

bun install
bun run typecheck
bun run test