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

Annotations already cover read-only, idempotent, non-destructive, open-world, so the remaining burden is light. The description still adds real value by disclosing that the returned total may be exact or estimated and by warning against conflating the preview sample size with the true count — both behavioral facts absent from the structured fields.

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, front-loaded with the core action, and the caveat about exact-vs-estimated counts follows immediately. Nothing is redundant with the name or title.

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?

There is no output schema, and the description does cover the return surface (a count plus an exact/estimated indicator). Given the very large undocumented filter object it could say more about which filters are meaningful for counting, but for a single-parameter read tool the core contract is present.

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?

Only one top-level parameter, but it is a nested object with roughly 25 filter fields at 0% schema description coverage, so the description carries most of the explanatory burden. Saying the tool counts 'all supplied filters' conveys that filters are ANDed and permissive, but it explains none of the individual fields (email_status, location scopes, max_results). This is a marginal addition over the schema rather than real parameter guidance.

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 ('Get the free match count') and scopes it to 'all supplied filters', which is enough to separate it from search_leads or preview_leads. It stops short of naming those siblings explicitly, so it is clear but not fully differentiated.

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?

Usage is only implied: the 'free' framing and the warning about preview sample size suggest calling this before a paid search. There is no explicit when-to-use statement, no named alternative, and no note on whether filters must match those later passed to search_leads.

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