json-contracts = generator

json-contracts = schema contract registry + validator

developer writes code
TypeScript validates it

agent writes JSON
json-contracts validates it

User
  ↓
Agent using whatever model the user picked
  ↓
json-contracts MCP server
  - lists available JSON contracts
  - returns schemas, rules, examples, and instructions
  - validates agent-produced JSON
  - returns repair contracts when validation fails
  ↓
Agent generates or repairs JSON itself
  ↓
App consumes valid JSON

npm install -g json-contracts
json-contracts --help

npx -y json-contracts@latest

mkdir my-json-contracts
cd my-json-contracts
npx -y json-contracts@latest init
npx -y json-contracts@latest validate

npx -y json-contracts@latest validate --contracts ./json-contracts
npx -y json-contracts@latest lint --strict --contracts ./json-contracts

./json-contracts

{
  "mcpServers": {
    "json-contracts": {
      "command": "npx",
      "args": ["-y", "json-contracts@latest"],
      "env": {
        "JSON_CONTRACTS_DIR": "./json-contracts"
      }
    }
  }
}

{
  "mcpServers": {
    "json-contracts": {
      "command": "npx",
      "args": ["-y", "json-contracts@latest"],
      "env": {
        "JSON_CONTRACTS_DIR": "/absolute/path/to/json-contracts"
      }
    }
  }
}

{
  "mcpServers": {
    "json-contracts": {
      "command": "npx",
      "args": ["-y", "json-contracts@latest"],
      "env": {
        "JSON_CONTRACTS_DIR": "./json-contracts"
      }
    }
  }
}

{
  "name": "json-contracts",
  "command": "npx",
  "args": ["-y", "json-contracts@latest"],
  "env": {
    "JSON_CONTRACTS_DIR": "./json-contracts"
  }
}

{
  "command": "json-contracts",
  "args": []
}

json-contracts/support-ticket.json
json-contracts/real-estate-lead.json
json-contracts/chart-generation.json

{
  "contract": "real-estate-lead",
  "input": "I'm pre-approved for a 4 bedroom house in Durham NC up to 900k.",
  "context": {
    "current_datetime": "2026-05-03T00:00:00Z",
    "email": "JohnnyAppleseed@gmail.com",
    "source": "website-lead-form"
  }
}

When converting natural language into app JSON, use json-contracts.

Create flow:
1. Call get_json_contract with contract, input, and context.
2. Generate JSON using the returned schema, rules, examples, input, and context.
3. Call validate_json.
4. If invalid, call get_repair_contract, repair the JSON, and validate again.
5. Return only validated JSON to the app.

Edit flow:
1. Call get_edit_contract with contract, currentJson, input, and context.
2. Return the complete updated object, not a patch.
3. Call validate_json.
4. Repair and validate again if needed.

Never skip validation. Never add fields that are not allowed by the schema. Do not copy context fields into output unless the schema allows them and the contract rules say to use them.

user input + app context
  -> get_json_contract or get_edit_contract
  -> your chosen model generates JSON
  -> validate_json
  -> if invalid: get_repair_contract -> model repairs -> validate_json
  -> app consumes valid JSON

json-contracts/support-ticket.json -> support-ticket

{
  "description": "Convert natural language into a support ticket object.",
  "rules": [
    "If the user says urgent, severity must be critical.",
    "Summary must be under 80 characters.",
    "Category must be authentication, billing, bug, feature_request, or other."
  ],
  "operations": {
    "create": {
      "enabled": true
    },
    "edit": {
      "enabled": true,
      "return": "full_object",
      "rules": [
        "Start from currentJson.",
        "Apply only the user's requested change.",
        "Preserve all unspecified fields exactly.",
        "Return the complete updated JSON object."
      ]
    }
  },
  "schema": {
    "type": "object",
    "additionalProperties": false,
    "properties": {
      "summary": {
        "type": "string",
        "maxLength": 80
      },
      "severity": {
        "type": "string",
        "enum": ["low", "medium", "high", "critical"]
      },
      "category": {
        "type": "string",
        "enum": ["authentication", "billing", "bug", "feature_request", "other"]
      }
    },
    "required": ["summary", "severity", "category"]
  },
  "examples": [
    {
      "input": "Urgent, users cannot log in after SSO update.",
      "output": {
        "summary": "Users cannot log in after SSO update",
        "severity": "critical",
        "category": "authentication"
      }
    }
  ]
}