> ## Documentation Index
> Fetch the complete documentation index at: https://sella.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Sella architecture: MCP, payments, and the marketplace

> Sella runs as two cooperating services behind one MCP interface. Agents never call them directly — the nine MCP tools handle everything.

Sella is built from two cooperating servers that sit behind a single agent interface. You never call them directly — the [MCP tools](/reference/mcp-tools) wrap everything — but understanding what's underneath helps you reason about latency, resilience, and cost.

## The two servers

Both services work together to power the full agent commerce loop: one handles the marketplace itself, the other owns API provider discovery and proxying.

<CardGroup cols={2}>
  <Card title="Sella Core" icon="server" href="/reference/mcp-tools">
    The marketplace, dashboards, auth, the MCP endpoint (`/api/mcp`), and the x402 payment gateway. Manages the dataset catalogue, dataset file storage, and orchestrates Cradle and Merge GPU jobs on your behalf — no infrastructure to configure.
  </Card>

  <Card title="API Data Market" icon="network" href="/consumers/api-market">
    A standalone service that manages the 1,400+ provider registry, normalises and classifies providers, and proxies paid calls with x402 or MPP.
  </Card>
</CardGroup>

These services are intentionally separate. When `list_market_apis` fetches from the Data Market backend, it uses a short timeout and falls back to a static catalogue if the backend is unavailable — so discovery stays resilient even during partial outages.

## Payments

Every paid call settles through an [x402](/reference/x402) facilitator in USDC. A chain-agnostic router selects the settlement chain per product — **Base, Solana, and Stellar** are live, with more on the way — and the runtime `402` challenge names the exact chain and amount for each transaction.

<Note>
  The challenge is authoritative. Always read the chain, amount, and recipient from the live `402` response — never hard-code them, because they vary per listing and per payment option.
</Note>

## Where Sella sits in the landscape

Most ways an agent can buy something today are either **point tools** (a single paid endpoint) or **human-operated platforms** (a dashboard with a checkout). Sella occupies the corner that is both agent-native and a full marketplace — data, compute, and APIs, with payment built into the protocol.

<CardGroup cols={2}>
  <Card title="Not just discovery" icon="magnifying-glass" href="/consumers/discover">
    Finding an API is table stakes. Sella also evaluates, pays, and delivers — all in one uninterrupted flow, without leaving the agent's context.
  </Card>

  <Card title="No human in the loop" icon="robot" href="/consumers/operators">
    Agents authenticate, hold wallets, and settle payments themselves, governed by the policies you set in your SKILLS.md file.
  </Card>
</CardGroup>