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

Annotations only cover readOnlyHint, and the description goes well beyond that: it discloses that numbers are approximate versus the in-app report, that coverage is limited to what the API key can see, and that a single call can issue at most 100 FUB requests. Those are real behavioral constraints an agent cannot infer from 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?

Purpose is front-loaded in the first clause, followed by use case, caveats and limits; every sentence carries actionable content. The trailing API endpoint listing (GET /v1/people totals, GET /v1/users) is implementation detail that adds minor clutter for an agent deciding how to call the tool.

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 no output schema and a 5-parameter tool, the description explains what is counted (per-agent source counts, conversion to closed stages, per-lender counts) and the visibility/approximation caveats. It stops short of indicating the shape or grouping of the returned result, which is the one remaining gap.

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 description adds meaning by tying the parameters to the underlying request budget ('one per count') and clarifying that lender counting is a separate dimension controlled by includeLenders. It does not restate syntax, but it explains parameter intent beyond the schema text.

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 set: counts leads by lead source per assigned agent, conversion to closed stages, and leads per lender user. It explicitly distinguishes itself from the sibling fub_search_people as the counting alternative, so an agent can route without opening either schema.

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?

Gives an explicit when-to-use rule ('Use it to count instead of paging through fub_search_people') and names the alternative it replaces. It also adds a pre-condition on credentials ('use an owner, admin or broker key for the whole account'), which is exactly the kind of guidance that prevents a wrong call.

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