Count matching leads (free)

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

Beyond the readOnly/idempotent annotations, the description discloses the economics that matter for this API: the call never spends credits, the $0.04 flat realtime price at Tier 0, and the fact that realtime runs only when explicitly requested. The consistency between 'never spends credits' and readOnlyHint=true reinforces trust rather than contradicting it.

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 sentences, front-loaded with the core outcome, then the free/paid distinction, then the realtime cost caveat. Every sentence carries weight; the only mild inefficiency is the slightly convoluted first clause ('what pulling them would cost at this account's prices').

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?

With 36 parameters, a 100% documented schema, and an output schema present, the description does not need to restate filters or return shape. It covers the two things the schema cannot: that the default path is free and that realtime billing is opt-in. A brief note on the two-level ICP (company_filters) would have made it fully complete.

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%, so the baseline is 3 and the schema already documents mode, strict, exclude_ids and the rest in depth. The description still adds value the schema does not: the concrete realtime price and the warning that passing mode:'realtime' is what triggers billing, which turns an enum choice into a cost decision.

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?

The description states a specific resource and outcome — how many leads match an ICP and what pulling them would cost — and explicitly separates itself from search_leads ('the first step before search_leads'). Even though it is phrased as a question rather than a verb, an agent can immediately tell this is a sizing/counting tool, not a row-returning one.

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 clear routing logic: use this first to size an audience for free, then call search_leads to actually pull rows, and avoid mode:'realtime' unless you accept a $0.04 charge. The one gap is that the sibling count_companies (the company-side equivalent) is never mentioned, so the leads-versus-companies choice is left implicit.

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