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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavior: the file never passes through the conversation and the caller receives a link, which changes how an agent must handle the result. It also cites the underlying API endpoint.

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?

Three short sentences, each carrying distinct information (what it is, how it is delivered, where the API is documented). The opening fragment is terse rather than front-loaded with a verb, and the raw API link is mildly noisy, but there is no filler.

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?

An output schema exists, so return-value explanation is not required. However, for a tool sitting in a dense inbox cluster with several near-neighbors, the missing routing guidance and the unresolved 'folder' vs 'file' Id ambiguity leave gaps an agent must resolve by trial.

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 single Id parameter is documented, giving a baseline of 3. The endpoint template GET /3/inbox/{Id} mildly clarifies that Id is an inbox item identifier, but it does not resolve the schema's confusing 'identifies the folder' wording, so no extra credit is earned.

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 conveys the resource (a file from the Fortnox inbox) and the delivery mechanism (a link the person opens), but never states the verb explicitly and never distinguishes itself from close siblings such as read_inbox_file or get_inbox. An agent can infer it produces a download link rather than file content, but must guess at the boundary.

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 and no mention of alternatives, despite the sibling list containing read_inbox_file, get_inbox, list_inboxes and list_unprocessed_inbox. The agent gets no rule for choosing download vs. read vs. list.

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