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

Beyond the annotations (write, non-destructive, open-world), the description discloses state effects: a payment below the balance leaves the invoice open, one that covers it marks the invoice settled. It also flags the external side effect ('Reaches other people: confirm with the user before each call') and the auth requirement (Cotlet API key with app access).

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?

Content is front-loaded with the core action and effect, followed by prerequisites and confirmation policy. It is dense but each sentence carries information; a couple of platform-level remarks could be trimmed.

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 write tool with no output schema and a fully documented 4-param schema, the description covers effects, prerequisites, confirmation, and auth. Only the absence of explicit alternative-tool routing keeps it from being fully 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?

Schema description coverage is 100%, so the schema already documents all four parameters with formats and defaults. The description adds semantic context for amount (partial vs. full behavior) but no syntax or format detail beyond the schema, so the baseline 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 states a specific verb and resource ('register a received payment, full or partial, on a customer invoice') and ties it to the concrete UI action ('like Registrer ny innbetaling in Fiken'). An agent can distinguish this from other payment-related siblings 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?

It gives explicit prerequisites: read the balance with get_invoice first, and source the bank account from list_bank_accounts. It also states the confirmation policy by default. It does not name alternative sibling tools (e.g. other payment-recording endpoints), so it stops short of full when/when-not routing.

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