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

The description says 'no request leaves this worker', indicating a local/offline validator, while annotations declare openWorldHint=true (open-world interaction). That is a direct contradiction, so the score is 1 and the contradiction is flagged. The otherwise useful detail about local list checking and unrecognised-vs-nonexistent semantics cannot overcome that conflict.

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?

Three sentences, front-loaded with the core function and then the critical limitation. No filler, and the limitation is stated clearly.

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 one-parameter deterministic validator with an output schema, the description covers purpose, limits, and semantics completely. The only issue is annotation consistency, not missing description content.

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 coverage is 100% and the single vpa parameter is already documented in the schema. The description adds meaning by explaining the validation dimensions (local-part syntax, PSP handle list, length rules) beyond the schema's example.

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?

Specific verb and resource: 'Deterministic structural validation of an Indian UPI Virtual Payment Address'. It states exactly what is checked (local-part syntax, handle against a local PSP list, length rules), so it is distinguishable from generic format validators among the siblings.

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?

Explicitly states when not to rely on it: not a live registry lookup, no request leaves the worker, unlisted handle means unrecognised rather than nonexistent, and it does not establish registration, reachability or ownership. It does not point to an alternative tool for live lookup, so 4 rather than 5.

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