# Choose HTTP, SDK or MCP

Choose the smallest applicable free or authorized paid interface.

Canonical: https://402signal.com/developers/interfaces

## Use the smallest tool that answers the task

 | Interface | Use it for | Do not infer

 | preview | Free catalog discovery without a new probe. | Fresh availability or signed evidence.

 | validate | Free readiness of one exact catalog-listed HTTPS endpoint. | Settlement, delivery or unrestricted URL testing.

 | HTTP /route | Supported current offer evaluation against buyer requirements. | Automatic seller execution.

 | Local guard | Offline evidence verification before the buyer's callback. | Wallet control or exactly-once payment execution.

 | Buyer adapters | The documented bounded lifecycle and recovery composition. | Universal merchant compatibility or permission to spend.

[OpenAPI](/openapi.json) defines HTTP inputs. [GET /rails](/rails) lists supported payment rails. The [MCP manifest](/mcp.json) defines the actual exposed tools. Bounded POST and batch/session profiles are HTTP-only unless explicitly present in the advertised MCP input schema.

The credential-free Glama stdio adapter supports preview and validate. It cannot sign, forward payment headers or complete a paid route. Paid routing requires a capable HTTP client with separately authorized payment. The versioned hosted MCP transport is `/mcp/v0.3.1`; HTTP recovery remains separate.

### For coding agents

Use these task guides or the [optional customer skill](https://github.com/402signalhq/402signal/blob/main/skills/402signal-buyer-checks/SKILL.md). Install or load it through your host's supported process. A file on GitHub is not globally available to every agent.

The copyable briefs are instructions for a chosen task, not new spending authority. Do not ask for wallet keys just to run an offline check. An ordinary free API request does not need a paid route.

[Markdown task index](https://github.com/402signalhq/402signal/blob/main/docs/customer/README.md) · [Machine-readable service guide](/llms.txt) · [MCP adapter](https://github.com/402signalhq/402signal/blob/main/integration/mcp/README.md).