# The four faces (/docs/concepts/four-faces)



kestrel.markets is one API with four equal surfaces. **HTTP + SSE is canonical.**
The TypeScript SDK, the CLI, and MCP are thin projections over the same operations —
not separate implementations, and none privileged.

```
HTTP + SSE
  ├── TypeScript SDK
  ├── CLI
  └── MCP
```

All four return the same operation IDs, events, receipts, diagnostics, and
artifacts. There are no face-only shortcuts and no impoverished MCP wrappers. A
session started on one face is inspected and resumed on any other. (The published
CLI runs the local runtime **and** is platform-connected today — `sim`, `prove`,
`certify`, and `verify` all reach `api.kestrel.markets`; the fuller mode driving
arbitrary hosted sessions from every verb lands later. See [CLI](#cli).)

## The elegance test [#the-elegance-test]

The whole public surface is seven operations (ADR-0004): discover, browse, check,
run, score, prove, continue.

```
GET  /.well-known/kestrel-markets
GET  /catalog
POST /validate
POST /simulate
POST /grade
GET  /proof/{id}
GET  /offers/{id}
```

Everything else is a rendering, a meter, or a receipt.

## The faces [#the-faces]

### HTTP + SSE [#http-sse]

The canonical face. Every operation is a plain HTTP request; long-running work
streams progress and receipts over Server-Sent Events. The other three faces are
generated projections of exactly these endpoints — nothing is added or hidden.

### TypeScript SDK [#typescript-sdk]

A typed client that mirrors the HTTP surface one-to-one: the same operation IDs,
events, receipts, and artifacts, with types generated from the same contract. No
SDK-only conveniences that the wire protocol lacks.

### CLI [#cli]

`npx kestrel.markets` runs the open-source local runtime — parse, frame, grade,
and replay against the committed regime tapes, entirely on your machine — and is
**platform-connected today**: `sim`, `prove`, `certify`, and `verify` reach
`api.kestrel.markets` to shareable proof URLs, free and anonymous. The fuller
mode — the same seven operations from a terminal, driving arbitrary hosted
sessions resumable on any other face — lands later.

### MCP [#mcp]

A Model Context Protocol projection so agents drive the platform natively. It is
a thin, equal wrapper over the canonical endpoints — never an impoverished
subset.

## The website is a fifth client [#the-website-is-a-fifth-client]

This documentation site is itself a plain client of the same public API — never a
privileged face. Agents that prefer markdown can read every docs page, including
the home page, as clean markdown on the same URL via `Accept: text/markdown`
content negotiation, fetch the home page directly at `/home.md`, or start from the
`llms.txt` corpus, which links a pre-built markdown twin of every docs page.