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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds a genuinely useful behavioral fact not in structured data: amounts are bare numbers with no currency, which directly prevents a wrong answer being reported. It is silent on return shape/pagination defaults, which the schema covers.

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 sentences, zero waste: the purpose and filter axes come first, and the currency gotcha — the highest-value information — is placed last as an actionable instruction. Nothing redundant or padded.

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?

With no output schema, the description carries return-value burden and does disclose the key trap (currency-less amounts) plus the remedy. It omits any indication of what an invoice record otherwise contains or the automatic all-pages fetch behavior, though the latter is covered in the 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 schema already documents all six parameters including the status values and the auto-pagination behavior. The description repeats the status enum and names vendor/project filters without adding format or ID-type detail beyond the schema, so the baseline 3 applies.

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+resource ("List invoices") and enumerates the filter axes (status, vendor, project), which is more than a restatement of the title. It does not, however, distinguish itself from the sibling get_invoice or explain the read-all vs. single-record relationship, so it stops short of a 5.

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?

Gives clear context for when the tool applies (filtering invoices by status/vendor/project) and explicitly names a companion call — get_organization_settings for currency_code — with the triggering condition (before stating an amount). No exclusions are stated, so it falls short of the 5-level when/when-not framing.

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