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

Annotations declare a non-read, non-destructive write, and the description adds genuinely new context beyond them: append-only behavior, the original being left untouched, posting into an open period, and the required 'book' scope. It does not say what happens if no open period exists or how failures surface, which keeps it from a 5.

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?

A single dense paragraph that front-loads the core mechanic before use case, validation, auth scope, and arguments. Every sentence carries information; nothing is redundant with the schema or annotations.

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 no output schema, the description covers behavior, the append-only guarantee, the use case, auth scope, and argument formats. Minor gaps remain, such as preconditions on the target voucher and error behavior, but nothing essential to a correct call 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 only 33% (only orgnr is documented in the schema), so the description must compensate. It supplies the date format (YYYY-MM-DD) and its 'default today' behavior, and enumerates the argument set including which is optional, though it does not clarify what voucher_id must reference.

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 effect: correct a voucher by posting a mirror voucher with reversed signs, leaving the original intact. This mechanic cleanly distinguishes it from siblings like book_voucher, create_voucher, get_voucher, and edit_voucher_draft, which do not reverse an existing posting.

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?

Gives a concrete when-to-use condition: correcting an entry whose period is locked, which is exactly the scenario that rules out edit_voucher_draft. It does not name sibling alternatives explicitly or state when NOT to use it (e.g. for open-period drafts), so it stops short of full routing guidance.

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