# What every API gets

URL: /interfaces · Id: `page:/interfaces`

> Every Interface, machine register and path an API serves from its one Definition, on its own host.

Every API on the platform serves all of the following from its one [Definition](/reference/concepts#definition), on its own host, with no code of its own.

## Interfaces
| Interface | At | What it is |
| --- | --- | --- |
| <a id="api"></a>API | `each operation path` | REST over HTTP: one GET per operation, answering JSON with a cost header and a request id. |
| <a id="mcp"></a>MCP | `/mcp` | Streamable HTTP with three tools for every API, never one tool per operation. |
| <a id="docs"></a>Docs | `/docs` | An index and one page per operation, Markdown first, with the HTML rendered from it. |
| <a id="sdk"></a>SDK | `/sdk` | One-file TypeScript and Python clients, generated from the Definition and served by the API. |
| <a id="app"></a>App | `/dashboard` | One [Key](/callers/keys) and its calls, in HTML, Markdown and JSON. |

## Machine registers
| Register | At | What it holds |
| --- | --- | --- |
| <a id="openapi"></a>OpenAPI 3.1 | `/openapi.json` | Every operation, its parameters, its return schema and its example. |
| <a id="llms-txt"></a>llms.txt | `/llms.txt` | Every operation with its route, in one plain text file for agents. |
| <a id="markdown-twin"></a>Markdown twin | `/docs/{verb}.md` | Each docs page as Markdown, the source its HTML is rendered from. |
| <a id="agents-json"></a>agents.json | `/.well-known/agents.json` | The card an agent reads first: what the API does, where its other registers are, and its price. |
| <a id="pricing"></a>Pricing document | `/pricing` | The posted price of every operation and the calls a month that cost nothing. |

## MCP tools
| Tool | Input | Answers |
| --- | --- | --- |
| `search` | `{query}` | The operations whose words match, each with its docs page. |
| `fetch` | `{id}` | The answer of a REST path as text, or the docs page of an operation as Markdown. |
| `do` | `{verb, input}` | Runs one operation; its structured content is exactly the REST body. |

## Reserved paths
| Path | Serves |
| --- | --- |
| `/` | The root JSON: the API name, its operations and its other registers. |
| `/mcp` | The MCP server. |
| `/docs` | The docs, in HTML or Markdown. |
| `/openapi.json` | The OpenAPI 3.1 document. |
| `/llms.txt` | The llms.txt file. |
| `/pricing` | The pricing document. |
| `/.well-known` | The agents.json card. |
| `/sdk` | The generated SDK files. |
| `/batch` | The [Batch](/reference/concepts#batch) route. |
| `/dashboard` | The [Dashboard](/reference/concepts#dashboard). |

## On every response
| Header | Carries |
| --- | --- |
| `X-Cost` | The price of the call, the upstream cost of serving it, and the currency. |
| `X-Request-Id` | The id a caller quotes when asking about a call. |