UCPList vs UCPChecker: Directory vs Validator

Two Tools, Two Jobs

We get this question a lot: "What is the difference between UCPList and UCPChecker?" Fair question. Both are tools in the UCP ecosystem. Both deal with UCP implementations. But they solve fundamentally different problems.

The short version: UCPList is a directory. UCPChecker is a validator. One helps you find things. The other helps you verify things. Both are useful. They are complementary, not competing.

What UCPList Does

UCPList is the discovery layer for the UCP ecosystem. It answers the question: "What exists?"

When you visit UCPList.ai, you get a searchable, categorized directory of everything in the UCP ecosystem: merchants with UCP endpoints, platforms with native UCP support, payment handlers that support token exchange, developer tools and SDKs, and agent integrations that use UCP for commerce.

Each listing includes:

• Current UCP status (Live, Announced, or Ecosystem participant)
• Category and capabilities
• Description and key details
• Verification status and date
• Links to the tool, documentation, or endpoint

UCPList is built for three audiences. Developers building UCP integrations who need to find SDKs, validators, and reference implementations. Merchants evaluating UCP who want to see what platforms and tools support it. Agent builders looking for UCP-enabled merchants and payment handlers to integrate with.

The directory is curated and verified. We check that listed tools actually exist and work. The data is also open source at GitHub, so anyone can contribute listings or corrections.

What UCPChecker Does

UCPChecker is a validation tool. It answers the question: "Is this implementation correct?"

When you point UCPChecker at a UCP endpoint, it runs a suite of checks against that specific implementation:

• Does the endpoint respond with valid JSON?
• Are all required fields present in the product data?
• Are data types correct (numbers are numbers, URLs are URLs)?
• Does the response conform to the UCP specification structure?
• Are checkout URLs reachable?
• How fast does the endpoint respond?

UCPChecker is built for developers and merchants who have already built or enabled a UCP endpoint and need to verify it works correctly before going live. It is a QA tool. You run it, it tells you what is broken, you fix it, you run it again.

When to Use Each

Use UCPList when you need to find something. Looking for a Python SDK for UCP? Check the developer tools category. Want to know which payment handlers support UCP token exchange? Check the payment handlers category. Need to see which merchants are live with UCP? Check the merchants category.

Use UCPChecker when you need to validate something. Built a UCP endpoint and want to make sure it works? Run UCPChecker against it. Enabled UCP on your Shopify store and want to confirm the endpoint is returning correct data? UCPChecker will tell you. Debugging why an agent is not picking up your products? UCPChecker will flag the specific fields or structure issues causing the problem.

Use both when you are going from zero to live. Start with UCPList to find the right SDK or platform guide for your setup. Build your implementation. Then validate it with UCPChecker before going live. Then submit your listing to UCPList so agents and developers can discover you.

The Overlap

There is some overlap, and that is fine. UCPList includes a validator tool that performs basic UCP endpoint validation. It checks endpoint availability, required fields, and response format. This covers the most common issues.

UCPChecker goes deeper on validation. More checks, more detailed error reporting, edge case coverage. If you are debugging a tricky implementation issue, UCPChecker's deeper validation suite is more likely to catch it.

Think of it this way: UCPList's built-in validator is the smoke test. UCPChecker is the full test suite.

Different Perspectives on the Ecosystem

UCPList takes a broad view. It tracks the entire ecosystem across categories: not just merchants, but platforms, payment handlers, developer tools, and agent integrations. It is useful for understanding the landscape and finding your way around.

UCPChecker takes a deep view. It focuses on one implementation at a time and tells you everything about whether that specific implementation is correct. It is useful for building and debugging.

Both perspectives are necessary. You need the map and the magnifying glass.

Our Honest Take

We built UCPList because the ecosystem needed a directory. People were struggling to find tools, merchants, and implementations. Discovery was fragmented across GitHub repos, blog posts, and word of mouth.

UCPChecker fills a different gap. It gives developers confidence that their implementation is correct before they expose it to agent traffic. That confidence matters. A broken UCP endpoint is worse than no endpoint at all because it trains agents to deprioritize you.

We are not competing with UCPChecker. We link to validation tools in our directory. We recommend validation as part of the implementation process. Both tools make the ecosystem better.

If you are just getting started with UCP, start here: browse the directory to understand what is available, find the tools you need, and use validation to make sure your implementation is solid before launch. The tools page has our built-in validator and links to other validation resources.