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

Goes well beyond the annotations (which already declare read-only, idempotent, non-destructive) by disclosing that invalid input never raises a protocol error but returns {"error": "<what is wrong and how to fix it>"}, and that retrying after correction is safe. It also flags the tool as FREE, which annotations do not convey.

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-loaded with the purpose and the FREE marker, and each subsequent sentence (example, when-to-use, scope caveat, error contract) carries information. It is somewhat dense as one flowing block, and the example return value partly duplicates the output 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?

For a three-parameter lookup tool it covers purpose, scope caveat, error behavior, retry safety, and usage triggers; the presence of an output schema means the return format needs no further explanation. Nothing an agent needs to call this correctly is missing.

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%, so country/year/subdiv semantics are already documented, and the description only adds a sample input ({"country": "IE", "year": 2026}). That example illustrates format but adds no constraint or meaning the schema lacks, so the baseline 3 applies.

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 ('List the public holidays the engine uses for a country and year') with explicit scope, and names its relationship to compute_deadlines, so an agent can separate it from sibling tools without opening a schema. The parenthetical naming of the underlying `holidays` package further pins down semantics.

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 when-to-use triggers ('checking why a business-day adjustment landed where it did', 'see whether a country/subdivision is supported') plus an explicit when-not ('Not a legal register of bank holidays'). It stops short of naming the closest sibling (list_regimes) as the alternative for the country-support question it mentions.

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