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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds useful behavior beyond them: it searches a large external catalog and 'Returns matching tools with links,' telling the agent what comes back in the absence of an output schema. It does not mention whether a no-match result is possible or how results are ranked.

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?

Front-loaded with the verb and resource in the first clause, and ends with the decision rule. The parenthetical list of 170+ tool categories is dense but serves query formulation; slightly longer than strictly needed.

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, read-only catalog search with full annotations and no output schema, the description covers scope (170+ tools, which domains), the return shape (matching tools with links), and the routing condition. Nothing an agent needs to invoke it correctly 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 coverage is 100% and the query parameter already documents itself with examples matching the description's phrasing. The description's category list loosely hints at good query terms but adds no real syntax or format guidance beyond the schema. Baseline 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 (Search) plus the exact resource: SendPay Business's library of 170+ free calculators, checkers and generators. The enumerated domains and examples (invoice generator, VAT, card fees, IBAN, forex) make it unmistakably a catalog search, clearly distinguished from the single-purpose sibling calculators like vat_calculator or iban_checker.

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 final sentence gives an explicit routing rule: 'Use it when the user needs a calculator or tool that is not offered directly here.' That both states when to use it and implicitly names the alternative path (the direct sibling tools), leaving little inference required.

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