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

Annotations declare non-read-only, idempotent, non-destructive, and the description goes well beyond them: it discloses the side effect of creating debtor-number customer records and linking invoices, confirms nothing is overwritten/deleted, confirms repeat calls add nothing (consistent with idempotentHint), and clarifies it does not email. That is exactly the extra context the annotation bar asks for.

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-loaded with the action and result, then prerequisites, then side effects; each sentence carries distinct information. The first sentence is dense with clauses but nothing is wasted.

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?

Covers purpose, preconditions, side effects, idempotency, and return payload (ZIP with counts and warnings) despite having no output schema; an agent has everything needed to decide and call correctly.

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 baseline is 3; the description adds real value by clarifying both are ISO dates (YYYY-MM-DD) and that the input date format is independent of the sender's format, and that only finalized invoices in the range are exported.

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 (builds a DATEV export), the exact resource (booking batch and master data CSV files), the scope (finalized invoices between from and to), and the return format (base64 ZIP with counts and warnings). No sibling tool does anything similar, so an agent can differentiate it immediately.

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?

Explicitly says when to use it ('when the user or their tax advisor needs the bookkeeping export') and states hard preconditions (German sender address, DATEV consultant and client numbers in sender settings), which even points an agent at get_sender_settings to verify.

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