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

Goes well beyond the annotations (write, open-world, non-destructive) by disclosing channel-specific constraints: SMS reaches only Norwegian numbers, eFaktura requires approved info exchange and hand-registered payments unless a KID agreement exists, and letters incur an extra charge for Norwegian addresses only. It also flags the per-call confirmation default and that it reaches external people, which is exactly the operational context an agent needs before invoking.

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?

Front-loads the purpose, then layers channel rules and safety details; nearly every sentence carries usable information. It is a bit dense and could be trimmed slightly, 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?

For an open-world write tool with no output schema, the description covers what gets sent, the channel caveats, the confirmation requirement, and the API-key/access prerequisite. Nothing an agent needs to call it safely is missing.

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 real meaning to the method enum by explaining the auto fallback order and the limitations of each channel. It does not expand on message, recipient_email, or include_attachments beyond the schema text.

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 (send) and resource (invoice) plus the delivery channels (EHF, eFaktura, email, SMS, letter), and clarifies it operates on an already-issued invoice. This distinguishes it from siblings like fiken_create_invoice and fiken_create_invoice_draft without needing to open 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?

Explains the trigger context ('as the sending window after Opprett faktura does') and what method=auto does, giving the agent a clear sense of when this tool applies. It does not explicitly name a sibling alternative or an exclusion condition, so it stops short of a 5.

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