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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, but the description adds meaningful context: it previews without locking, uses the same logic as the VAT page, and does not change anything. It could go slightly further by describing the response shape or whether figures are cached, but the behavioral profile is well covered.

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 tightly written and front-loads the key distinction: preview without locking. Every sentence contributes to purpose, usage, or safety context, with no redundant restatement of the title or schema.

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?

There is no output schema, but the description explains that the tool returns a 9-box VAT breakdown derived from the period's transactions. Combined with the safety annotations, this is enough for an agent to call it correctly, though it does not detail the structure of the returned figures.

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 description coverage is 100%, so both parameters are already documented in the schema. The description does not add syntax or formatting details about period_id or company beyond what the schema provides, so the 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?

States a specific verb and resource: previews a 9-box VAT breakdown for a period without locking it. It distinguishes itself from related tools like lock_vat_period and explains the calculation basis, so an agent can identify its role 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 names when to use it, including example user phrases such as "what's my VAT for this quarter" and the pre-lock review workflow. It also positions it relative to lock_vat_period, leaving no ambiguity about when this preview tool is appropriate.

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