Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, openWorld and non-destructive. The description adds value beyond them by stating it reads one public file, stores nothing, and calls no checkout endpoint, plus that no API key is needed. The return shape (verdict, per-rule results, fix list) is described, though an output schema exists, so that earns less credit.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Four tight sentences, front-loaded with what the tool is and where the file lives, then mode selection, then return shape, then safety and auth constraints. No filler and nothing repeated needlessly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-optional-parameter read-only validator with full schema coverage and an output schema, the description covers everything an agent needs: both invocation modes, the mutual-exclusion rule, the return shape, and the safety/auth profile. Nothing material is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the schema itself documents both parameters and the exactly-one-of constraint. The description restates the fetch-vs-paste distinction and adds the 'public store' qualifier, but adds no syntax, format, or error-handling detail beyond what the schema provides, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (validate) and resource (a store's ACP discovery file at /.well-known/acp.json), and names the protocol explicitly, which distinguishes it from the sibling ucp.validate. An agent can tell what this does and which protocol it governs without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear mode-selection guidance: pass url to fetch a public store's file, or document to check pasted JSON. It also notes no API key is required, lowering invocation friction. It does not, however, explicitly point to ucp.validate as the alternative for UCP files, so the sibling routing is left implicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.