Required Fields Validator

Cloudflare Workers + TypeScript MCP server for the single app required-fields-validator.

Project purpose

Required Fields Validator checks whether submitted fields include required fields and returns a structured validation result. The app is read-only, deterministic, and scoped to field completeness validation.

Project structure

• src/index.ts - Cloudflare Worker routes, review shell pages, challenge route, MCP methods, and tool logic.
• tests/routes.test.ts - Route, challenge, and MCP regression tests.
• wrangler.jsonc - Cloudflare Worker configuration.
• package.json - Local scripts and development dependencies.
• README.md - Setup, deployment, and operations notes.

Routes

• GET /
• GET /privacy
• GET /terms
• GET /support
• GET /health
• GET /.well-known/openai-apps-challenge
• POST /mcp

MCP Methods

• initialize
• tools/list
• tools/call

Tool

• validate_required_fields

The tool checks submitted field keys against required field names and returns structuredContent matching the declared outputSchema. It is deterministic and does not call external APIs, write to databases, submit forms, or update external systems.

Local development

npm install
npm run typecheck
npm test
npm run dev

When running locally, set OPENAI_APPS_CHALLENGE if you need to test the challenge route with a non-empty value.

PowerShell example:

$env:OPENAI_APPS_CHALLENGE = "your-token"
npm run dev

Deployment

Deploy with Wrangler:

npm run deploy

The deployed Worker must expose POST /mcp directly. Do not use an app slug prefix for the MCP endpoint.

Environment variables

• OPENAI_APPS_CHALLENGE - Plain text token returned by GET /.well-known/openai-apps-challenge.

The challenge route returns the environment variable value as plain text. It does not return JSON and does not hard-code a token.

Online URLs

• Home: https://required-fields-validator.<your-workers-subdomain>.workers.dev/
• Privacy: https://required-fields-validator.<your-workers-subdomain>.workers.dev/privacy
• Terms: https://required-fields-validator.<your-workers-subdomain>.workers.dev/terms
• Support: https://required-fields-validator.<your-workers-subdomain>.workers.dev/support
• Health: https://required-fields-validator.<your-workers-subdomain>.workers.dev/health
• Challenge: https://required-fields-validator.<your-workers-subdomain>.workers.dev/.well-known/openai-apps-challenge
• MCP: https://required-fields-validator.<your-workers-subdomain>.workers.dev/mcp

Replace <your-workers-subdomain> with the deployed Cloudflare Workers subdomain shown by Wrangler.

Common failures

• Challenge route is empty: set OPENAI_APPS_CHALLENGE in the Worker environment and redeploy.
• MCP route returns not found: call POST /mcp, not an app-prefixed route.
• TypeScript fails after dependency changes: run npm install, then npm run typecheck.
• Local route tests fail: run npm test and inspect the failing route or MCP method.
• Deploy fails due to authentication: sign in with Wrangler for the target Cloudflare account, then rerun the deploy command.