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

Annotations already declare readOnlyHint=true, so the safety profile is covered and the bar is lower. The description usefully discloses what the response contains (items, amounts, relation), which matters because no output schema exists, but it says nothing about pagination, error behavior, or permissions.

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 compact sentences with the returned content front-loaded and the endpoint pattern following. There is essentially no waste, though the raw endpoint string is somewhat redundant with the tool name. Appropriately sized for a one-parameter read tool.

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 get-by-id tool with full schema coverage and readOnly annotations, the description supplies the one thing structured fields lack: what the returned invoice includes. No output schema exists, so this return-content note is the key piece and it is present, if brief.

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 single id parameter is already documented in the schema, including its source (eboekhouden_list_invoices). The description adds no further semantics such as id format or constraints, so the baseline of 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 resource ('one invoice with its items, amounts and relation') and effectively implies the retrieval verb through 'GET /v1/invoice/{id}'. An agent can tell it apart from eboekhouden_list_invoices because it clearly returns a single entity rather than a collection. It stops short of explicit sibling differentiation, but the singular scope is unambiguous.

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?

No when-to-use guidance or alternatives are given in the description. It never states that this is the correct tool for fetching a single invoice by id versus using eboekhouden_list_invoices or eboekhouden_list_outstanding_invoices. The only hint about the id source lives in the schema parameter description, not the tool description.

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