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

Beyond the readOnlyHint annotation, the description adds specific guarantees: 'Writes nothing: no play, no ICP row, no cache.' It also discloses the null return when no data-provider key is configured and explains the write-scoped key requirement as a gateway quirk, not a real mutation. These details materially prevent agent confusion.

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 achieve a lot: the core question/result, the no-write guarantee, the concrete use case, the null edge case, and the auth nuance. Everything earns its place, and the most decision-relevant facts are front-loaded.

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 simple estimation tool with three optional filters, no output schema, and limited complexity, the description covers the return shape ('≈ N companies match'), the null case, side-effect behavior, and intended workflow. An agent has everything it needs to call this tool correctly.

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%: sizes, locations, and industries each have a description with examples. The tool description itself does not expand on parameter semantics, but the schema carries that load. The iterative example ('widen the locations') hints at how the locations parameter is used, but that is marginal beyond the schema.

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 opens with the exact question the tool answers ('How big an audience a CANDIDATE ICP would reach') and the result format ('≈ N companies match'). It clearly scopes the tool to pre-commitment estimation, distinguishing it from sibling tools that create or update plays and ICPs.

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 description gives an explicit iterative workflow: 'propose facets → see 40 → widen the locations → see 900 → then create the play.' This makes the when obvious (before committing, during iteration). It does not explicitly name a sibling alternative or spell out when-not-to-use, but the 'before committing' and 'then create the play' cues are strong.

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