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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds only the API path reference, which confirms the read semantics and gives a doc link but discloses no new behavior such as error/not-found handling or whether the response is the raw Fortnox payload.

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 short sentences, purpose front-loaded, zero padding. The documentation URL is marginally useful but does consume space without adding actionable instruction.

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?

A low-complexity single-parameter read tool with a full annotation set and an output schema, so return values need not be explained. The only real gap is the missing routing guidance against list_customers, which is a modest omission for a tool this simple.

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% and the single CustomerNumber parameter is documented in the schema as 'Customer number of customer to show'. The description mirrors that via the {CustomerNumber} path template but adds no format, example, or lookup hint beyond the schema.

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 ('Retrieve a customer') with the exact underlying endpoint, so the agent knows this is a single-record fetch. However it never distinguishes itself from the obvious sibling list_customers, leaving the singular-vs-list distinction to be inferred from the name alone.

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?

There is no guidance on when to use this versus list_customers, find_customer_invoices, or propose_create_customer. No prerequisites, no exclusions, no mention of what happens if the CustomerNumber does not exist.

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