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

No annotations are provided, so the description carries full responsibility. It transparently explains the GB vs NI rules, the month-minus-a-day pitfall, and the consequence of testing too early ('quietly loses weeks of cover'). It does not describe the output format or error handling, but for a date-calculating tool the key behavioral nuances are disclosed.

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 efficiently structured: it states the core purpose first, then explains the regional rules and the critical pitfall, and ends with a clear usage directive. Every sentence earns its place, though it is slightly longer than necessary for a simple date tool. Front-loading is effective.

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 tool has moderate complexity due to regional variation and the month-minus-a-day subtlety, all of which the description covers. The schema fully documents both parameters, and the description explains the rules that govern their use. No output schema exists, but the return value (dates) is inferable. It lacks explicit handling of edge cases like expired MOT, but the described scenarios are complete for typical use.

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?

The schema description coverage is 100%, so both parameters already have thorough descriptions. The tool description adds contextual rules (GB/NI) that help interpret which parameter to use, but it doesn't add parameter-specific semantics beyond what the schema provides. Baseline of 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 opens with a specific verb ('Work out') and resource ('when a car's MOT test is due'), and immediately clarifies it also returns the earliest safe test date. It explicitly distinguishes from sibling tools like calculate_car_tax and check_clean_air_zone by focusing on MOT timing. The scope is unambiguous.

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 states 'Use for any question about MOT due dates, MOT timing, or when a car needs testing,' which is a clear directive. It doesn't explicitly exclude other tools or name alternatives, but the sibling list shows unrelated topics (tax, emissions, pricing), so the usage context is effectively clear. Lacking an explicit 'do not use for X' costs one point.

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