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

Annotations already declare readOnlyHint=true, so safety is covered. The description goes beyond by disclosing that invoices return line items and a public share link, adding behavioral context that is not present in 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?

Two short sentences. The primary action is front-loaded, and the invoice-specific addition is concise and valuable. No wasted words.

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, the description covers the essential behavior and the notable invoice extra. It does not mention return format or all resource specifics, but these are not necessary given the simplicity and the schema enum.

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 50% (id has a description, resource has only an enum). The description does not elaborate on parameters, but the resource enum is self-explanatory. This falls at the baseline; no added value from the description, but no gap that breaks usage.

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?

Description states a specific verb ('Fetch') and resource ('single record by id'), and adds a useful detail about invoices. It is clear even without explicitly naming siblings; the contrast with 'fawtar_list' is implicit but apparent.

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 conveys that this is for fetching one record by id, which implies when to use it. It does not explicitly mention alternatives or exclusions, but the context of sibling tools (create, list, etc.) makes the use case evident.

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