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

Annotations already declare the safety profile (not read-only, idempotent, non-destructive), but the description adds critical context: no request is sent to Fortnox, the change is only prepared for approval, and the response explains how the approved change is sent. It does not cover auth, rate limits, or proposal lifetime, but it discloses the key side-effect boundary.

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?

Four short sentences, front-loaded with the purpose and endpoint, followed by the critical approval/no-send caveat and body shape. Every sentence contributes useful information without padding.

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 annotations and an output schema available, the description covers purpose, endpoint, side-effect boundary, and body wrapper adequately. The main missing piece is explicit routing among the many proposal, execution, and resolution tools in the sibling set.

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%, so the baseline is 3, but the description adds useful meaning: DocumentNumber is shown as the URL path variable, and the body is described with the expected Fortnox Invoice wrapper shape. It still does not document individual invoice fields, but it improves on the generic schema descriptions.

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 ('Update an invoice') and the exact Fortnox endpoint PUT /3/invoices/{DocumentNumber}. The approval-only clause distinguishes it from tools that execute writes, so an agent can tell what it does without opening the 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?

Explains that this tool only prepares a change for a person to approve and sends nothing to Fortnox, which gives clear context for using it in an approval workflow rather than direct execution. It does not explicitly name execute_fortnox_write, resolve_fortnox_write, or propose_fortnox_write as alternatives, so the routing guidance is not exhaustive.

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