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

Annotations already establish readOnly and idempotent behavior menu, so the description only adds 'compact totals only' which clarifies the output granularity. This is mild added value, not rich behavioral context. No contradiction with annotations.

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?

The description is a single, focused sentence that states purpose and output characteristics. It is front-loaded and avoids unnecessary details, making it highly concise and efficient.

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?

Given the tool has 4 parameters, no schema description, and no output schema, the description leaves significant gaps. It does not explain parameter formats, defaults, or interactions, nor does it mention any limitations. Only the basic purpose is covered, which is insufficient for full operational guidance.

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 description coverage is 0% and the description does not explain any of the four parameters (account, end_date, days_back, start_date). It mentions grouping dimensions but not the filtering parameters. With no compensation from the description, parameter semantics are virtually absent.

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 uses a specific verb 'Query' and names the resource ('normalized GCP Billing BigQuery export') and the grouping dimensions (day, service, project, SKU). It clearly distinguishes from siblings like gcp_billing_top_services by specifying the full cost breakdown.

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 implies when to use the tool (to get detailed cost breakdowns) and gives a clear context for cost analysis, but does not explicitly state when not to use it or mention alternatives. Since siblings are not referenced, it falls short of a 5 but meets the 'clear context' bar.

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