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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral detail beyond that: omitting both dates returns the entire recorded history, which signals a potentially large unbounded response. It does not mention ordering or result limits, keeping it short of a 5.

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 short sentences, no filler. The core purpose and return shape come first, with the default-scope caveat and sibling routing following in priority order.

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 read tool with full schema coverage and explicit annotations, this covers purpose, default scope, output shape (no output schema exists, so this matters), and the sibling alternative. Nothing needed to call it correctly is missing.

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 parameter formats (YYYY-MM-DD, surface id from surface_list) are already documented and set the baseline at 3. The description adds the meaning of omitting start_date/end_date together, which the schema does not state, but nothing about partial ranges or inclusive/exclusive boundaries.

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 the exact resource and granularity ('Sessions per day for a surface') and even the return shape ('as {date, sessions}'), then names the sibling it is not for conversion/winners. An agent can distinguish it from surface_results 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 the omitted-argument semantics explicitly ('With no dates, every recorded day') and routes conversion/winners queries to surface_results. Clear context and one named alternative, though it does not spell out other cases such as an invalid or unknown surface_id.

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