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

Annotations already cover the safety profile (readOnly, openWorld, idempotent), so the bar is lower. The description adds genuinely non-structured behavior: a 100-hit page cap and a pay-per-call model ('0.01 USDC per successful call (x402, Base). Errors are free.'), which materially affects an agent's decision to call and expected failure handling.

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 dense sentences with zero filler: filters first, then the invocation constraint, then pagination and pricing. Nothing is repeated from the schema or annotations and every clause carries 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 6-parameter, zero-required search tool with no output schema, the description covers what can be filtered, the page cap, and the payment mechanics. It stops short of describing what a hit contains or whether pagination beyond the cap is supported, minor gaps given annotations carry the safety profile.

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%, so baseline is 3. The description still adds value by clarifying that the name search covers 'current and former names' and by naming the register/classification standard (TOL 2008), details the schema's terse 'Name, or part of it' does not convey.

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 and resource ('Search Finnish companies from the PRH trade register') and enumerates the exact filter dimensions (name, town/city, company form, TOL 2008 industry code, postcode). It is unmistakably a company search, though it never distinguishes itself from the sibling 'search_companies', so an agent cannot tell the two apart from the description alone.

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?

'Give at least one filter' is an explicit invocation precondition that prevents an unbounded query, and the schema confirms zero required parameters, making this guidance load-bearing. However, no alternative tools (e.g. get_company for a single known company) or when-not conditions are named.

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