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

Annotations already cover the safety profile (readOnly, non-destructive, openWorld), and the description adds real behavioral context: default sort order (newest issue date first), pagination at up to 100 per page, and an auth requirement (Cotlet API key with app access). These go beyond the annotations, though return format detail is only partially covered.

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?

Front-loads purpose and scope, then layers behavior and item fields. Most sentences earn their place, though the item-field enumeration is somewhat listy and could be trimmed given the schema already implies the domain.

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 usefully enumerates returned item fields (number, kind, status, buyer, net, VAT, gross, due date, paid amount), plus pagination and auth needs. This is largely complete for a 9-param list tool, missing only edge-case behavior like empty results or rate limits.

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 coverage is 100%, so the schema already documents all 9 parameters including the income flag and period. The description restates the income=false meaning rather than adding syntax or defaults beyond the schema. It also mentions 'unless you set order,' referencing an 'order' parameter that does not exist in the schema, which slightly muddies parameter semantics.

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 (list) and resource (invoices) with clear scope: sales or cost invoices for a chosen period, returning status, totals and due date. An agent can distinguish it from get_invoice, create_invoice, or list_clients in the same family without opening a schema.

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?

Usage is implied through the period and income filtering guidance, but there is no explicit when-to-use versus alternatives routing (e.g., 'use get_invoice for a single invoice'). The guidance is adequate but leaves the agent to infer when this list tool is the right choice over siblings.

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