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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine behavioral value beyond that: the response includes an explicit notCovered list, and it enumerates the actual coverage scope (tax years, country sets, the 14 EOL products, etc.), which tells the agent what to expect back.

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 purpose and the "call before assuming" instruction are correctly front-loaded, but the description then unfolds into a single enormous run-on sentence enumerating the return contents of every area. Much of that enumeration restates what the tool itself will return, which is bloat rather than necessary pre-call information.

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?

With no output schema, the description carries the full burden of describing returns, and it does so thoroughly: area names, the shape of the coverage data, and the presence of a notCovered list. An agent has everything needed to decide whether to call it and with which area.

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% and the enum values are already listed in the schema, so baseline is 3. The description goes further by mapping each area name to its contents (e.g. calendar = holidays/tax years/DST for named countries, uk-gov-process = passports/DVLA/voting), which adds meaning the bare enum does not carry.

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 specific, unusual verb+resource: it reports exactly what Data Butler covers and does not, per area, which an agent can distinguish from data-fetching siblings like uk_rates_lookup or take_home_pay. It does not explicitly name or contrast with the closest sibling, catalogue, so it falls short of a 5.

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?

"call this before assuming something is unsupported" gives explicit, actionable timing for invocation, and "omit for all" clarifies the no-argument case. There is no stated when-not condition or comparison against the catalogue sibling, so it is clear context rather than full routing guidance.

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