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

It adds behavioral context beyond the annotations: the call returns a voucher number, is refused when the float is exceeded, rejects byte-identical duplicates, and mentions the free-tier quota. The only weakness is that the duplicate refusal is stated absolutely even though the schema's duplicate_ok parameter can override it.

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?

The description is two tight sentences with no filler. The core action, return value, failure conditions, and quota are each given one crisp clause, and all information earns its place.

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?

The schema covers parameter semantics, and the description covers the return value, refusal conditions, and rate limit. The only gap is the missing duplicate_ok caveat in the duplicate-refusal statement; otherwise an agent would have what it needs to invoke the tool 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?

All eight parameters are already documented in the input schema with 100% coverage, so the description does not need to repeat them. It adds no parameter-level nuance beyond the 'tin' metaphor, making the schema the primary source of parameter meaning.

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 precise verb and resource: 'Record one voucher paid out of the tin' and even names the returned identifier format, VOU-YYYY-NNNN. This clearly separates it from the float, license, reconcile, and voucher_delete siblings.

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?

The recording use case is implied by the title and verb, and the description gives explicit refusal conditions such as exceeding the float and duplicate vouchers. However, it does not name any sibling tool or explain when to prefer voucher_add over alternatives like topup_record or voucher_delete.

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