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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds an explicit authentication requirement and names the output categories, which provides useful context beyond the annotations. No contradiction exists.

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, compact sentence with the core operation and output categories front-loaded. The redundant tool-name prefix is minor but slightly prevents a perfect score for structure.

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 read-only tool with one optional parameter and no output schema, the description provides enough invocation context and enumerates the expected output categories. It misses no critical call-time information.

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%, and the schema itself explains the sessionKey parameter and when to pass or omit it. The description only reinforces that authentication is required and does not add new parameter-level meaning, so baseline 3 is appropriate.

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 names a specific verb and resource ('Get summary statistics of invoices') and enumerates the exact aggregates returned: total paid, pending, and overdue amounts. This clearly distinguishes it from listInvoices (raw list) and getInvoiceDetails (single-invoice detail).

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 intended use case is implied by the phrase 'summary statistics of invoices,' but the description does not explicitly say when to use this tool over listInvoices or getInvoiceDetails, nor does it state exclusions. It is adequate but not explicit.

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