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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context about the return content: every line, tax breakdown, and the open balance after credit notes. The parenthetical 'see credited_minor' is somewhat cryptic but does not contradict 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?

The description is a single, front-loaded sentence that communicates the core action and return contents efficiently. The parenthetical 'see credited_minor' is slightly ambiguous, but it does not significantly bloat the description.

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?

Given the tool is a simple single-parameter read operation, the description covers the most important contextual aspects: what is returned, the scope, and the credit-note balance nuance. There is no output schema, so describing the return contents is valuable. The description is sufficient for an agent to select and invoke the tool correctly in most cases, though it omits error behavior for missing invoices.

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 only provides a required 'number' parameter with zero description coverage. The description adds the key semantic that this is an invoice number, which is essential. However, it does not specify expected format, examples, or edge cases, and with 0% schema coverage a stronger parameter explanation would have been helpful.

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 states a specific verb ('Return'), a specific resource ('the full stored record for one invoice number'), and the exact scope (one invoice). It clearly distinguishes itself from invoice_list by focusing on a single full record and from invoice_pdf by returning the stored record rather than a generated document.

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 implies usage: call this tool when you need the complete stored record for one invoice number. However, it does not explicitly specify when not to use it or name alternatives such as invoice_list for summaries or invoice_pdf for a document. The contrast with list-like siblings is only implicit.

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