SchemaGate

What it does

Post an LLM output string and a JSON Schema; receive a binary valid/invalid verdict plus a hint describing the validation failure. Use this as the last step before treating LLM output as structured data. Prevents downstream type errors, broken pipelines, and hallucinated field names from propagating.

When to use it

• Validate LLM-generated JSON before inserting into a database
• Gate a multi-step pipeline on schema compliance
• Retry loops: validate → retry if invalid

Request schema

{
  "response": "{\"name\": \"Acme Corp\", \"revenue\": \"not a number\"}",
  "schema": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "revenue": {
        "type": "number"
      }
    },
    "required": [
      "name",
      "revenue"
    ]
  }
}

Response schema

{
  "valid": false,
  "hint": "revenue: expected number, got string"
}

Code example — TypeScript via MCP

Install the MCP server once; all 16 services become tool calls.

// Configure @melis-ai/x402-tools-mcp in your MCP client
// Then call the tool:

const result = await mcpClient.callTool("schemagate", {
  "response": "{\"name\": \"Acme Corp\", \"revenue\": \"not a number\"}",
  "schema": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "revenue": {
        "type": "number"
      }
    },
    "required": [
      "name",
      "revenue"
    ]
  }
});

console.log(result);
// ["valid","hint"]...

Code example — Python via direct HTTP

import requests

# x402 payment header must be set by your wallet client
# See x402.org for client libraries

headers = {
    "Content-Type": "application/json",
    "x-payment": "<signed-x402-payment-header>",
}

resp = requests.post(
    "https://schemagate.melis.ai/validate-schema",
    json={
      "response": "{\"name\": \"Acme Corp\", \"revenue\": \"not a number\"}",
      "schema": {
        "type": "object",
        "properties": {
          "name": {
            "type": "string"
          },
          "revenue": {
            "type": "number"
          }
        },
        "required": [
          "name",
          "revenue"
        ]
      }
    },
    headers=headers,
)
print(resp.json())

Code example — curl with internal key bypass

For testing with an issued internal key (skips x402 payment flow):

curl -X POST https://schemagate.melis.ai/validate-schema \
  -H "Content-Type: application/json" \
  -H "x-internal-key: YOUR_KEY" \
  -d '{"response":"{\"name\": \"Acme Corp\", \"revenue\": \"not a number\"}","schema":{"type":"object","properties":{"name":{"type":"string"},"revenue":{"type":"number"}},"required":["name","revenue"]}}'

Related services

FAQ