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

Annotations already declare readOnlyHint/idempotentHint/non-destructive/closed-world, so safety is covered. The description adds genuinely new behavioral context the annotations lack: the OAuth requirement and plan-tier gating. Minor gap: no statement about rate limits or behavior on invalid codes.

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?

Two sentences with zero waste; the core purpose is front-loaded, followed immediately by the input format and prerequisites. Nothing repeats the title or annotations.

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 single-parameter, annotation-rich, no-output-schema tool, the description covers purpose, input format, and access requirements adequately. It briefly notes output shape ('each label comes with the full code') but could mention behavior on unknown codes.

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 0%, so the description must compensate, and it does: it explains the array-of-codes input, that the check digit is optional, and gives concrete examples ('45000000-7', '79952000'). It omits the maxItems=500 bound, but the core format ambiguity is resolved.

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+resource: 'Resolve CPV codes to their Polish labels', which is clearly distinct from browsing tools like cpv_tree or cpv_search. It does not explicitly name those siblings or state when they should be preferred, so it falls short of a 5.

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?

It gives useful invocation context: pass an array of codes, check digit optional, and that OAuth plus a trial/paid plan is required. However, it never says when to use this rather than cpv_search or cpv_tree, so the alternative-selection guidance is only implied.

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