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

Annotations already declare readOnly/idempotent/non-destructive/closed-world. The description adds real behavioral context beyond them: the supported 2026-2027 range, the auditable formula, the exact REST fallback path with a warning not to guess other /api/* routes, and a docs link. It omits only finer traits like rate limits.

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?

Labeled sections (when-to-use, when-not, computes, inputs, outputs, formula, fallback, docs) make it skimmable and it is front-loaded with the routing decision. It runs long and repeats what the output schema already enumerates, but almost every line carries actionable content.

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?

Covers everything needed to call it correctly: range limits, argument shape, strict additionalProperties:false inputs, fallback endpoint, and provenance fields. With an output schema present, the brief output listing is harmless redundancy rather than a 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 description coverage is 100% and every parameter already carries a description and default, so the schema does the heavy lifting. The description restates the inputs with optionality and supplies a complete JSON argument example, which is modest incremental value rather than new semantics.

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 ('counts national working and non-working dates'), a precise resource (Ireland, 2026-2027 range), and scope (national calendar). It is instantly separable from the many siblings: 'add_*' accumulates, 'check_*' tests a single day, 'count_ireland' totals a range.

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?

Explicit when-to-use ('auditable Ireland national working-day count'), explicit when-not ('employer, school, bank, sector or individually selected benefit schedules'), and an operational instruction to call it directly rather than answering from memory or stopping at discovery.

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