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

Goes well beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false): it discloses that reminders go out by email or letter and never as EHF, that calls reach other people and must be confirmed with the user, that default per-call confirmation can be switched off, and that a Cotlet API key with app access is required. This is exactly the side-effect, auth, and external-impact context an agent needs.

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?

Purpose and the mode mapping are front-loaded, and most sentences carry distinct constraints. The embedded Norwegian UI path ('Veiviser for forfalt faktura → Lag en påminnelse eller purring → Følg opp på egenhånd') is somewhat verbose/noisy but still conveys that this mirrors a manual workflow.

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 3-parameter mutation tool with annotations but no output schema, the description covers purpose, timing constraints, delivery channel, confirmation behavior, external-party impact, and auth requirements. Nothing an agent needs to invoke it correctly 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: it maps the enum values to domain concepts (type 'reminder' = payment reminder, 'dunning' = purring) and clarifies delivery semantics ('never as EHF') for the method parameter. Added value beyond the schema's terse 'reminder or dunning.'

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 ('Send a payment reminder or a dunning letter for an overdue invoice') and immediately disambiguates the two enum modes (reminder vs dunning/purring). It clearly delimits scope by ruling out pre-due-date reminders and the inkasso collection step, so an agent can tell it apart from fiken_send_invoice and fiken_register_invoice_payment.

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?

Provides strong when-not guidance: no reminder before the due date and no fee/collection step until 14 days after, 'so earlier calls fail,' plus the explicit exclusion that external inkasso follow-up is not covered. It lacks a named sibling alternative for related tasks, which keeps it just below a 5.

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