# A2ui Validate — MCP tool `findutils:a2ui_validate`

Validates a JSONL A2UI payload against the basic catalog (or a custom catalog) and returns any errors, warnings, or info messages with exact line numbers. Call this on every LLM-generated payload before sending to the client.

- Category: developer
- MCP server: https://mcp.findutils.com/ (Streamable HTTP, no API keys, 120 req/min per IP)
- Reference page: https://findutils.com/mcp/a2ui-validate/

## Connect

```bash
claude mcp add findutils --transport http https://mcp.findutils.com/
```

Claude Desktop (`claude_desktop_config.json`):

```json
{
  "mcpServers": {
    "findutils": {
      "url": "https://mcp.findutils.com/"
    }
  }
}
```

## Call the tool (verified example)

```bash
curl -X POST https://mcp.findutils.com/ \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/call",
    "params": {
      "name": "a2ui_validate",
      "arguments": {
        "payload": "{\"version\":\"v0.9\",\"createSurface\":{\"surfaceId\":\"s\",\"catalogId\":\"x\"}}"
      }
    }
  }'
```

Example arguments (verified):

```json
{
  "payload": "{\"version\":\"v0.9\",\"createSurface\":{\"surfaceId\":\"s\",\"catalogId\":\"x\"}}"
}
```

Decoded `payload` argument (readability only — send it as a string):

```json
{
  "version": "v0.9",
  "createSurface": {
    "surfaceId": "s",
    "catalogId": "x"
  }
}
```

---
Full catalog: POST https://mcp.findutils.com/ with method `tools/list` · https://findutils.com/mcp/ · https://findutils.com/llms.txt