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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes further with details annotations cannot carry: return shape (today_holiday plus days until next), ISO 8601 format localized to the region, and a concrete rate limit (100 free calls per client per UTC day, then $0.001 USDC per call via x402). The region-divergence caveat adds a correctness-relevant warning.

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?

Front-loads the core behavior and keeps the whole thing to a few tight sentences. The pricing sentence is useful but slightly weighty relative to the rest; still, each sentence carries distinct, non-redundant 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 supplies the return fields (next holiday, today_holiday, days until) and the date format, plus key discovery and cost model. An agent has everything needed to call it correctly without follow-up guessing.

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 each parameter is already documented with examples, so the baseline is 3. The description adds meaning beyond the schema by explaining why region matters (constituent UK countries have different holidays) and directing the agent to list_regions for valid keys, which reduces key-guessing errors.

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 ('Returns the next bank (public) holiday for a region') and clarifies scope by noting it also returns today's holiday and the day count. It is clearly distinguishable from a plural listing tool, but it never names or contrasts with its sibling list_bank_holidays, so sibling differentiation is inferred rather than stated.

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?

Gives concrete usage context: call list_regions first for valid country/region keys, and choose the correct region because England, Scotland, Wales and Northern Ireland differ. It does not state when to prefer/avoid this over list_bank_holidays, but the ordering prerequisite and region-selection guidance are explicit.

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