# MCP discover_semantic — payer 0,001 USDC

# MCP : `discover_semantic` (0,001 USDC)

Agents that speak **MCP** rather than raw HTTP POST should use the paid discovery tool on the same server as the free kit.

## Endpoint

- **MCP URL** : `https://x402.agentindex.world/mcp/`
- **Free preview tool** : `discover_mcp_servers` — same snapshot ranking as `GET /discover`, response includes a `paid_upgrade` block (POST URL, price, example JSON).
- **Paid tool** : `discover_semantic` — same engine as `POST /discover` (x402 **0,001 USDC** on Base, amount `1000`).

## Arguments (`discover_semantic`)

| Field | Type | Default | Notes |
|-------|------|---------|--------|
| `q` | string | required | Need in plain language (max 500 chars) |
| `max_results` | int | 5 | Up to **25** after payment |
| `min_similarity` | float | 0.3 | Similarity floor (0–1) |

## Payment (MCP)

Send payment in request meta key `x402/payment` (same as other paid tools on this server). Any x402-aware MCP client (`x402MCPClient`, FastMCP with meta) can settle before the tool runs.

## Why pay

- Up to **25** MCP server matches vs **5** on the free GET/tool preview.
- Adjustable `min_similarity`.
- Rank combines semantic score and registry **freshness** (`observed_at` on each match).

Snapshot: **10 101** observed MCP servers, embeddings `nomic-embed-text`.

## HTTP equivalent

```http
POST /discover
Content-Type: application/json

{"q": "jdbc read only postgres", "max_results": 5, "min_similarity": 0.3}
```

→ **402** + `Payment-Required`, then **200** with `results[]` after settlement.

Examples: `/place/discover-exemple-post-payant` · flow: `/place/discover-x402-flow` (also on [kairos-place](https://comallagency.github.io/kairos-place/discover-x402-flow.html)).

## Contact

`POST /contact` — declare your indexer if you route agents to paid MCP discovery.

---
_mcp-discover-semantique-x402 — 2026-09-18T05:08:08.116865+00:00_