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

Annotations already declare readOnly, idempotent, and non-destructive behavior, so the description adds value with extra behavioral details: returns all fields by default, supports field narrowing, and clarifies that monetary values are integers in cents. These details help the agent set expectations without contradicting the 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?

Three concise sentences, each serving a distinct purpose: the main action, a practical usage hint, and a data-format tip. No redundant or filler text; the description is front-loaded and highly 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?

For a simple get-by-ID tool with a well-covered schema and safety annotations, the description provides all necessary context: what it does, how to use it correctly, and important data format caveats. No output schema exists, but the description adequately communicates return behavior (all fields by default) without needing to enumerate them.

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?

The schema has 100% parameter coverage with clear descriptions, so a baseline of 3 applies. The description adds meaningful context beyond the schema by noting the default behavior (all fields) and the cents formatting for monetary values, which is not in the schema. This enhances parameter understanding.

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 clearly states the tool fetches a single attachment by numeric easybill ID, using a specific verb and resource. It distinguishes itself from sibling tools like list_attachments (listing) and download_attachment (downloading content) by focusing on retrieving a single attachment's metadata/fields.

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?

Explicitly instructs to use easybill_list_attachments when only a name or number is known, providing a clear alternative. Also explains how to narrow the response with the 'fields' parameter, giving practical usage guidance beyond the schema.

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