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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds meaningful behavioral detail beyond annotations: billed hours are excluded by default and lines are grouped per rate to prevent averaging. This helps the agent understand output semantics without needing to inspect the schema.

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 short sentences, each earning its place: purpose and output, billing exclusion behavior, and plan limitation. The key acting verb and resource appear first, and there is no filler or repetition beyond acceptable reinforcement.

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 read-only summary tool with four parameters and no output schema, the description covers the essential output contents and key behaviors. It could additionally state the exact response shape, but the 'invoice lines' and 'one line per rate' phrasing give enough structural expectation for an agent to proceed safely.

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 100%, and the input schema already explains from/to's free vs Pro period behavior and unbilled_only's default and effect. The description mostly restates these points ('Hours already marked billed are left out', 'Free: last 7 days') rather than adding new parameter-level meaning. Baseline 3 is appropriate because the schema carries the detail.

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 starts with a specific verb and resource: turning tracked billable time into invoice lines for one project. It clearly enumerates the output fields (hours, hourly rate, amount per task, total) and adds a distinguishing behavior (one line per rate, no averaging), which separates it from sibling tools like report and export_csv.

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 clear context: this is for one project, converts billable time into invoice lines, and covers a billing period. It does not explicitly name alternatives or say when not to use it, but the 'for one project' and 'invoice lines' framing strongly imply its niche relative to report and export_csv.

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