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

Goes well beyond the readOnly/destructive annotations by disclosing the pricing rule (each entry at its logged rate, zero-rate entries counted at zero), the inclusion criteria (finished billable time and billable expenses), the default grouping, and the owner-only authorization requirement. An agent knows what happens to unpriced entries and who can call it.

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 core 'preview, does not create' claim and packs useful detail into a single dense sentence. It reads slightly as a run-on with nested parentheses, but every clause earns its place.

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 23-parameter preview tool with no output schema, the description adequately characterizes the returned content (lines and totals, grouped) and the pricing/authorization behavior. Some parameter-level nuance (date filters, expense/time inclusion flags) is left entirely to the schema, but nothing critical for correct invocation 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 description coverage is 87%, so the schema already documents nearly all 23 parameters including defaults. The description adds only the groupBy enum values and default, which slightly overlaps the schema field description. Baseline 3 is appropriate given the schema does the heavy lifting.

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 (shows/previews), a specific resource (the lines and totals of an invoice from a project's unbilled work), and explicitly negates the write behavior ('without creating anything or taking any hours'), which cleanly separates it from the sibling create_invoice_from_work.

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 phrase 'without creating anything or taking any hours' tells the agent exactly when this preview is appropriate versus the create counterpart, and 'Only the project owner' adds a permission precondition. It stops short of naming create_invoice_from_work as the alternative, so routing is implied rather than spelled out.

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