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

Annotations already declare readOnlyHint, openWorldHint=false and destructiveHint=false, so the description's added value is in stating 'Local arithmetic only' and 'Callable without an API key' — real operational facts about cost, auth, and offline execution. It does not describe what a failing checksum looks like, but the output schema covers the response shape.

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 short sentences with zero filler, and the core action and the scope limit are front-loaded. Every sentence adds distinct information.

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, offline, read-only utility with an output schema, the description covers what the agent needs: what is computed, that it is local, and that no registry is consulted. Only the input format convention is left unaddressed.

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 carries the burden. The weight list (6,5,7,2,3,4,5,6,7) implies a 9-digit checksum input, which is genuinely useful, but it never states the accepted input format (digits only vs. dashed like 123-456-32-18, despite maxLength 20).

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: 'Check the checksum of a Polish NIP', plus the exact weight vector. The negative clause 'Does not look the NIP up in any registry' cleanly separates it from registry-querying siblings such as check_vat_whitelist and vies_check.

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?

'Local arithmetic only' and 'Does not look the NIP up in any registry' make the when-to-use context clear without naming the alternative tools explicitly. Strong routing signal, but the sibling tools that should be used for registry lookups are never named.

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