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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely new behavioral context: the required credential scope ('user's Cotlet API key with access to this app') and the field-level contents of the returned record, which matters because there is no output schema.

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 core purpose and the auth requirement are front-loaded, which is good. But the field enumeration is duplicated: the opening fragment lists 'address, contacts, email addresses, VAT number, IBAN and payment term' and the next sentence repeats nearly the same fields at greater length, so a portion of the text does not earn 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 get-by-id tool with no output schema, the description does the heavy lifting by enumerating the returned fields (addresses, phone, invoice email, VAT number, registration number, IBAN, payment term, inactive flag) and stating the credential requirement. Missing only minor detail such as error behavior for an unknown ID.

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 parameter is documented in the schema itself ('Relation ID from list_relations'). The description adds no syntax or format detail beyond that, so the baseline 3 applies.

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 ('Get relation') and scopes it to a single record ('One relation', 'the full record of one relation'), which cleanly separates it from the sibling e-boekhouden_list_relations. An agent can tell what it returns without opening any 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?

Gives one concrete use case ('Use it before invoicing to see where the invoice will go'), which is useful context. However, it never names alternatives or exclusions (e.g. use list_relations to obtain the relation_id, or update_relation to modify), so the when-to-use guidance is implied rather than complete.

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