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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds context the annotations cannot: page size cap (100), the next_cursor -> cursor continuation pattern, and the auth requirement (Cotlet API key with app access). No return-shape detail is given, but that gap is minor since it lists the fields inline.

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-loaded with the resource and its fields, then usage, then pagination and auth. Slightly redundant, since sentence one ("Customers in the customer register…") and sentence two ("Lists customers from the Fortnox customer register") restate the same resource, but every other sentence earns its place.

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 read-only list tool with full annotation coverage and no output schema, the description covers purpose, fields, search semantics, pagination, auth, and sibling cross-references. Nothing an agent needs to call 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 description coverage is 100%, so the baseline is 3. The description adds value beyond the schema by clarifying what the search string can match (name, number, or organisation number) and how the cursor value from a prior response feeds the cursor parameter, going slightly beyond the schema's terser wording.

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 ("Lists") and resource ("customers from the Fortnox customer register") and enumerates the fields returned (number, name, organisation number, email). It also implicitly distinguishes itself from the write-side sibling by framing the search as a way to "check whether a customer exists before creating one."

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?

Explicit when-to-use guidance is given (search by name, customer number or organisation number to verify existence before creating) and it names the downstream sibling linkage ("Use the customer_number of an item in create_invoice"). The pagination condition is also stated, so the agent knows how to continue a result set.

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