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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds genuine value by disclosing the content of the result (grouped line items, totals and taxes, payments received, Peppol status) and naming the underlying Teamleader endpoint (invoices.info), which no structured field provides.

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?

A single sentence, front-loaded with the action and payload summary, followed by the API mapping. Nothing is wasted and nothing essential is buried.

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?

With no output schema, the field enumeration is what tells the agent what a 'full' invoice contains, which is the key missing structured information. A brief note on failure behavior for an invalid or unknown UUID would make it complete.

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?

There is a single required parameter whose schema description and UUID regex fully document its format (100% coverage). The description adds no syntax or format detail beyond that, 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?

The description opens with a specific verb and resource ('Fetch one invoice in full') and enumerates the data domains returned, so the agent knows exactly what comes back. It only implicitly distinguishes itself from teamleader_list_invoices via the word 'one' rather than naming the sibling.

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 rather than stated: fetch a single invoice when you have an invoice_id. There is no explicit guidance on when to prefer this over teamleader_list_invoices, and no note about prerequisites such as needing a valid existing UUID.

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