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

Annotations already declare readOnly/openWorld/non-destructive, so the safety profile is covered. The description adds genuinely new behavioral context: the item-level return shape (series, number, date, description, debit total) and an auth prerequisite ('Needs the user's Cotlet API key with access to this app'). It doesn't clarify pagination behavior beyond what the cursor param implies.

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 first sentence mostly restates the second ('vouchers in a voucher series and date range' vs 'filtered by voucher series and transaction date'), so there is redundancy. The phrase 'rows come with the voucher itself' is vague and adds little. It is not bloated, but every sentence does not fully earn 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?

For a read-only list tool with no output schema and full schema coverage, the description is nearly complete: it explains filters, workflow context, return fields, and auth. Pagination is only implied by the cursor parameter rather than stated, which is the main remaining gap.

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%, documenting all five parameters (to/from dates, limit, cursor, voucher_series), so the schema carries the load. The description only restates the filtering concept at a high level and adds nothing about the limit or cursor semantics. Baseline 3 is appropriate.

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 gives a specific verb ('Lists') and resource ('vouchers'), plus the scope ('one financial year, filtered by voucher series and transaction date'). An agent can immediately distinguish this read/list tool from siblings like create_voucher or get_invoice 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 names an explicit workflow and companion tool: 'Use it before create_voucher to see whether an entry for the period was already booked.' That is concrete, actionable context. It lacks any when-not-to-use or edge-case exclusions, so it stops at a solid 4 rather than 5.

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