Invoice summary

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

With no annotations, the description carries the full burden, and it discloses non-obvious behavior: already-billed hours are excluded, rates are never averaged, and the free plan is limited to the last 7 days. It does not state auth expectations or explicitly confirm read-only status, but it provides enough safety-relevant behavior for an agent to avoid misuse.

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 front-loaded sentences deliver the core action, scope, output shape, and constraints with no filler. The fragment 'Free: last 7 days' is compact but informative.

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?

Without an output schema, the description compensates by naming the output fields and aggregation rule. It does not spell out pagination or exact response formatting, but the core invocation details are recoverable from the description plus the fully described input schema.

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%, so the parameters are already fully documented. The description adds high-level context such as the free-period limit and line-per-rate output, but no per-parameter meaning beyond what the schema already provides.

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 opening phrase 'Turn tracked billable time into invoice lines for one project' names a concrete verb, resource, and scope. The additional behavior — one line per rate so two rates never average — clearly distinguishes it from broad reporting or export siblings.

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 never states when to use invoice_summary versus siblings like entry_list, report, or export_csv. It describes what the tool does but gives no when-to-use, when-not-to-use, or alternative routing guidance.

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