Proven DI core
A hierarchical Context of Bindings with
@inject, providers, interceptors, extension points,
and tag-based discovery — ported from LoopBack 4.
Agent-native, end to end
Interfaces agents use.
Backends agents
build.
AgentBack gives your REST endpoints, MCP tools, OpenAPI docs, typed
clients, and validation one Zod contract — one
schema, every boundary. Agents consume that surface with
machine-actionable errors, /llms.txt, and MCP tools;
and because there's a single source of truth, a coding agent can
author the whole surface from it without drift. Built on
LoopBack 4's proven dependency-injection core, rebuilt for ESM
and Node 22.
alpha · ESM-only · Node 22.13+ · TypeScript 6
const City = z.object({city: z.string().min(1)});
const Report = z.object({summary: z.string(), tempC: z.number()});
@api({basePath: '/weather'})
class WeatherController {
@get('/forecast/{city}', {path: City, response: Report})
async forecast(input: {path: z.infer<typeof City>}) { /* … */ }
}
@mcpServer()
class WeatherTools {
@tool('forecast', {input: City, output: Report})
async forecast(input: z.infer<typeof City>) { /* … */ }
}One artifact, many views
The Zod schema is the contract
Declare a schema once, on the decorator. The framework derives every other representation from it — so a coding agent adds a surface in one edit and nothing drifts.
- Runtime validatorrequests & tool calls parsed before your code runs
-
z.infertypethe handler's input type, enforced at compile time -
OpenAPI 3.1.1served at
/openapi.json, rendered in Swagger UI - MCP tool schemainput/output contracts on the official MCP SDK
-
/llms.txtagent-readable surface map from the same route registry - Typed clientno codegen — the client imports the same schemas
Positioning
For APIs that apps and agents consume
Most stacks keep the runtime contract, the service contract, and the agent contract in three hand-synchronized places.
| Stack | Runtime contract | Service contract | Agent/tool contract |
|---|---|---|---|
| Express + raw Zod | Hand-wired Zod | Hand-written OpenAPI | Hand-written manifest |
| Fastify | JSON Schema / TypeBox | OpenAPI via plugin | Custom adapter |
| Hono | Zod (validator) | OpenAPI via add-on | Custom adapter |
| tRPC | Zod | TypeScript-only | Custom adapter |
| NestJS | class-validator | Swagger decorators | Custom adapter |
| FastAPI | Pydantic | OpenAPI from same models | Custom adapter |
| AgentBack | Zod | OpenAPI from same Zod | MCP from same Zod |
Fastify and Hono are transport runtimes, not competitors. They solve HTTP plumbing; AgentBack solves the layer above — one Zod schema projected to REST, OpenAPI, and MCP through a DI container, riding on a host beneath it. Hono is the closest sibling in spirit (Web-standard core, codegen-free typed client, Zod), and AgentBack is built to stay host-portable so the same projection runs wherever the handler is mounted.
What's in the box
Agent ergonomics, end to end
Hybrid surfaces
REST and MCP servers are components over the same container. Run either, or both from one process — controllers and tool classes are just bindings.
Build a hybrid app →Errors agents can fix
Stable codes, per-field issues, the violated schema, retryability, and remediation hints — the same machine-actionable envelope on REST and MCP.
Read the design note →Safety primitives
confirm: payload-bound confirmation tokens and
idempotency: key replay, declared on the route or
tool that must not run twice.
Per-call pricing
@price('$0.001') meters a route or tool; the price
gate refuses unpaid calls with an x402/MPP challenge. Stripe
metered billing from the same usage log.
Typed client, no codegen
TypeScript consumers import the same schemas and get typed calls plus runtime validation — the client never imports a running server.
Contract-first clients →Tool-surface budgets
Every tool definition costs context-window tokens on every
connection. toolCostReport token-prices the MCP
surface before agents pay for it.
Production rails
Auth (JWT, OAuth 2.1), authorization voters, health probes, Prometheus metrics, OpenTelemetry, rate limiting, validated config — all as DI components.
Deploy to production →Documentation
A guided path, ideas first
Three ideas carry the whole framework: everything is a binding in a context, schemas live once on the decorator, and servers are components.
For coding agents
Hand the build to a coding agent
AgentBack ships an agent skill that teaches Claude Code, Codex, Cursor, and 20+ other agents the conventions that aren't guessable from type signatures — schema-on-decorator, the slot-0 input bundle, the DI container. One Zod schema is the only source of truth, so an agent adds a route, its MCP tool, and its docs in a single edit without drift. The docs are agent-readable too — /llms.txt, /llms-full.txt, and a markdown mirror of every page — so the agent reads the framework the way it reads your API.
# install the AgentBack skill into your agent of choice
npx skills add ninemindai/agentback
# point an agent at the docs corpus
curl -s https://agentback.dev/llms.txtBuilt with AgentBack
A worked example, end to end
Not a snippet — a real service. agentback-demo is a
Weather server where one Zod schema set is served over stdio,
authenticated HTTP, and a dev console. It's the shape a coding agent
and the skill produce: one contract fanning out to REST, MCP, a
typed client, and docs, with nothing kept in sync by hand.
One Zod schema set, served three ways — stdio, authenticated HTTP, and a dev console. Backed by the free Open-Meteo API.
- one schema → REST + MCP + typed client + docs
AgentError,/llms.txt, tool-cost report- the canonical agent-plus-skill build
Quick start
Run the examples in two minutes
AgentBack is in alpha — the end-to-end examples work and the API surface is still moving. Clone the repo and run a working REST, MCP, or hybrid app, each with its explorer UI.
# clone & build (tests and examples run against dist/)
git clone https://github.com/ninemindai/agentback
pnpm install && pnpm build
# REST + Swagger UI + Context Explorer
pnpm -F hello-rest start
# REST + MCP from one process, both UIs
pnpm -F hello-hybrid start