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

With readOnlyHint and destructiveHint already declared, the description still adds real value: it lists the returned fields (number, customer, amount, due date, status), explains that a concept invoice has no number and open invoices are unpaid, and notes the Cotlet API key with app access is required. It omits pagination/rate behavior, so not a 5.

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?

Purpose is front-loaded in the first sentence, and the status glossary that follows is informative rather than filler. Slight length cost from bilingual filter names, but no sentence is wasted.

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 list tool with fully covered parameters and no output schema, the description covers purpose, filter semantics, returned fields, and auth requirements. Nothing an agent needs to invoke it correctly is missing.

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 baseline is 3, but the description goes beyond the schema by mapping the status values to the Dutch overview filters (alles, concept, vervallen, openstaand, betaald) and clarifying what concept and open mean. It adds no detail on limit/cursor, keeping it from a 5.

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 and resource ('Lists sales invoices from the invoice overview, filtered by status'), clearly distinct from get_sales_invoice, create_sales_invoice, or issue_sales_invoice by name. It scopes the operation to the overview view. It doesn't explicitly name a sibling to avoid, 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?

Usage is implied by the filters described (status/customer), but there is no explicit when-to-use statement or routing to alternatives such as get_sales_invoice for a single record or list_customers for customer IDs. The status semantics give context but not guidance.

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