UCP Tools Compared: Validators, Monitors & Developer Tools
Not all UCP tools do the same thing. Validators tell you if your manifest is valid today. Monitors tell you if it stays valid tomorrow. Here's how the major tools compare.
Why Tool Choice Matters for UCP Compliance
UCP compliance isn't a one-time checkbox — it's an ongoing infrastructure requirement. A manifest that passes validation today can break tomorrow when a Shopify app updates, a CDN configuration changes, or a WAF starts blocking bot traffic. The tools you choose determine whether you catch those regressions in seconds or discover them when an AI agent fails to shop at your store.
There are now several tools in the ecosystem, each with a different focus. This page breaks them down so you can pick the right one for your workflow.
Feature Comparison Matrix
| Feature |
UCP Checker
This site
|
UCPtools.dev
|
Nextwaves
|
Google Official
|
ucpvalidator.app
|
|---|---|---|---|---|---|
| Real-time monitoring Ongoing checks, status alerts | ✓ | — | — | — | — |
| Bulk validation Check multiple domains at once | ✓ | — | ✓ | — | — |
| AI agent testing Live agent sessions against real stores | ✓ Playground | ✓ Endpoint probes | — | — | — |
| Chrome extension Auto-detect UCP while browsing | ✓ | — | — | — | — |
| Public API Validation and status API (early dataset snapshot on Hugging Face, not updated) | ✓ API | — | — | — | — |
| Platform guides Implementation walkthroughs by platform | ✓ | ✓ | — | ✓ | — |
| Profile / manifest generation Generate a UCP manifest for your store | — | ✓ | — | — | — |
| Grading system Score or letter grade for compliance | ✓ Runtime grade | ✓ Multi-level | ✓ A–F | — | — |
| Merchant directory Browse known UCP-enabled stores | ✓ 3,400+ stores | — | — | — | — |
| Free tier Available at no cost | ✓ | ✓ | ✓ | ✓ | ✓ |
Tool Profiles
UCP Checker This site
Monitor + ValidatorUCP Checker is the infrastructure layer of the UCP ecosystem. It continuously crawls 3,465+ merchants and re-checks them daily, so the directory always reflects live UCP status across the open web. That continuous, neutral coverage is the core product.
Beyond static validation, UCP Checker integrates with the UCP Playground — an environment that runs live AI agent sessions against real stores and feeds runtime performance scores back into the directory. This data cannot be derived from reading manifest files alone.
- 3,465+ merchants crawled and indexed
- Daily re-checks with email alerts on status change
- Live agent sessions via the UCP Playground (A–F runtime grade)
- Chrome extension for passive detection while browsing
- Early dataset snapshot on Hugging Face (April 2026, CC-BY 4.0, no longer updated)
- MCP server for AI agent integration
- Free public API for programmatic validation
UCPtools.dev
Validator + GeneratorUCPtools.dev is a developer-focused toolkit for building and validating UCP manifests. It offers multi-level validation and UCP profile generation — useful when you're starting from scratch. Note: their "agent simulation" probes endpoints but does not run real AI agent sessions like the UCP Playground.
- Multi-level validation: syntax, schema, spec conformance
- Endpoint probing (not live agent sessions)
- UCP profile and hosting artifact generation
- Signing key pair generation and management
- Platform implementation guides
Best for: Developers building their first UCP manifest who need a guided creation workflow.
Nextwaves
ValidatorNextwaves takes a test-centric approach to UCP validation, running 40+ individual tests against your manifest and grading the result with a letter grade from A to F. Each failing test comes with an actionable fix recommendation, making it useful for debugging specific compliance issues.
- 40+ automated validation tests
- A–F grading system
- Actionable fix recommendations for each failure
- Bulk domain validation
Best for: Teams who want a structured test report they can track through a remediation process.
Google Official (ucp.dev)
Spec + ReferenceThe official UCP specification site maintained by Google. It defines the standard, hosts the developer guides, and integrates with Google Merchant Center for stores joining the UCP ecosystem through Google's channels. Not a third-party validator — the authoritative source of truth for what the spec requires.
- Official protocol specification
- Developer implementation guides
- Google Merchant Center integration path
- Canonical schema definitions
Best for: Reading the spec and understanding what a conformant implementation must include.
ucpvalidator.app
Validatorucpvalidator.app is a lightweight compliance checker focused on fast, no-frills manifest validation. Enter a domain or paste a JSON manifest, get a pass/fail result against the spec. Simple and to the point.
- Quick compliance check against UCP spec
- Paste JSON or check by domain
- Clean, minimal interface
Best for: Quick spot-checks during development without needing to create an account.
The UCP Checker Ecosystem: Full-Stack UCP Infrastructure
UCP Checker is not just a validator — it's the infrastructure layer beneath a full stack of UCP tooling. While single-tool competitors focus on one part of the problem, the UCP Checker ecosystem covers the entire lifecycle: detecting UCP, monitoring it, testing it with real agents, orchestrating it at scale, and discovering merchants through a structured registry.
The core product. Continuously crawls and daily re-checks 3,465+ merchants, and grades compliance. Free API, Chrome extension, email alerts, and an MCP server for agent integration.
- Domain checker & public REST API
- Daily re-crawls with email alerts on status change
- A–F runtime grading via Playground data
- Merchant directory & open HF dataset
- Chrome extension for passive detection
Run real AI agent sessions against live stores. Claude, Gemini, and other models interact with actual MCP servers while you inspect every JSON-RPC call. Runtime performance feeds back as A–F grades into the UCP Checker directory.
- Multi-model support (Claude, Gemini, and more)
- Full JSON-RPC message inspection
- Checkout flow & capability testing
- Headless API for CI pipelines
- Session replay with OTel tracing
A structured registry for merchants, agents, and extensions. Provides API endpoints that let AI agents discover UCP-enabled stores, find compatible extensions, and look up agent capabilities — the discovery layer of the UCP stack.
- Merchant registry API for store discovery
- Agent registry for capability lookup
- Extensions & skills registry
- Structured schema for programmatic access
The MCP control plane for agents operating across UCP stores. UCP Rails sits between agents and stores — handling discovery, guardrails, memory, skills, and observability — without proxying the transaction itself.
- Agent memory (session, agent, user scopes)
- CEL guardrails for policy enforcement
- Skills & extensions execution layer
- Hooks & loops for automation
- OTel dual-export for full observability
Not just a validator: No other single tool covers this stack. UCPtools.dev validates your manifest. UCP Checker monitors whether it stays valid, tests it with real agents, orchestrates it at scale, and lets other agents discover it. Pick the right tool for each job — or use all of them.
Validators vs. Monitors: Understanding the Difference
Most UCP tools are validators — they check your manifest at a single point in time. This is useful when you're building, debugging, or preparing for a launch. But once your store is live, a validator only tells you the current state. It won't tell you if your manifest breaks next week.
There are two validators worth knowing about, each tackling a different layer. The UCP Validator audits your /.well-known/ucp manifest structure — required fields, transport bindings, signing keys, spec-version compliance. The UCP Catalog Validator audits what your catalog endpoints actually return — variant data, product completeness, pricing, response envelope, cross-capability round-trips. A manifest can validate while the catalog responses it points to still break agent shopping; both layers need their own audit.
Monitors re-check your manifest on a schedule and alert you when something changes. UCP Checker re-crawls verified merchants daily and sends email alerts when a store's status changes — from verified to unreachable, from valid to blocked, or back again.
The distinction matters for production infrastructure. A CDN misconfiguration can flip your status from verified to blocked in minutes. A platform update can invalidate fields you were relying on. A WAF rule can start rejecting our crawler. Without monitoring, you find out when an agent fails to shop at your store — not before.
The infrastructure analogy: Validators are like a building inspector who signs off on construction. Monitors are like a smoke alarm. You need both, but only one saves you at 3am.
The Data Advantage
UCP Checker maintains the largest continuously-updated index of UCP adoption on the open web — 3,465+ merchants, re-checked daily so the directory reflects live status rather than a one-off snapshot. It's available as:
- Individual status pages at
/status/{domain}— showing each store's current, latest-checked state - Public merchant directory at /directory — browseable, filterable, searchable
- Live adoption stats at /stats — platform-level and ecosystem-wide adoption data
- Dataset snapshot on Hugging Face — an early CSV snapshot from April 2026 under CC-BY 4.0, no longer updated
- Public API — programmatic access for custom integrations
No other tool indexes UCP adoption at this scale across the open web. The Playground adds a second dimension: runtime performance data from live AI agent sessions, graded A–F, that captures whether a manifest actually works when an agent tries to use it.
FAQ
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