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

Annotations only cover the safety profile (readOnly, idempotent, non-destructive, closed-world). The description goes well beyond by disclosing that it is free and needs no account, that covered areas are skipped, and that exact cost is impossible because billing is 1 token per newly discovered business. That billing and skip model is exactly the context annotations cannot carry.

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?

Front-loads the key qualifier ('FREE, no account needed') and keeps to three sentences. The final sentence explaining the cost ceiling is long and slightly conversational, but every sentence carries information an agent needs.

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, the description compensates by describing what comes back: a count of grid points plus already-covered areas. Combined with the explicit cost caveat, an agent has enough to call this correctly, though it never states the response shape or whether estimates are cached.

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 all four parameters, including the grid/city enum, are fully documented. The description hints at the 'grid points' concept but adds no syntax, defaults, or format detail beyond what the schema already supplies, so the baseline of 3 applies.

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 ('Size') and resource ('a search_areas run') and immediately clarifies the two things it quantifies: grid points and already-covered areas. An agent can distinguish it from the sibling search_areas (which executes the run) 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?

'Size a search_areas run before starting it' gives clear timing relative to the execution tool, and the note about skippable covered areas tells the agent why this matters. It does not name estimate_list, the sibling that sizes list-based searches, so the routing between the two estimate tools is left to inference.

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