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

With no annotations, the description fully discloses behavior: skips weekends and the 11 French holidays, uses Butcher-Meeus for movable feasts, explains mode semantics, deterministic local computation, JSON output, and price. This exceeds typical descriptions.

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 information-dense but compact; every clause adds value (behavior, modes, determinism, output, cost). It is front-loaded with the core purpose and uses concrete examples.

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 stateless calculation tool with no annotations or output schema, the description covers purpose, inputs, modes, holidays, and output type. It lacks only an explicit output shape, but 'JSON' is likely sufficient for an agent to invoke and parse.

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 0%, so the description is the only source of parameter meaning. It compensates well by explaining start/add with examples and adding from/to/mode semantics. However, the schema's required 'start' is not reconciled with the range mode using 'from', creating minor ambiguity.

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-resource pair ('Adds N French business days') and immediately distinguishes the two calculational modes (add vs range). It is unmistakably distinct from sibling validation/lookup tools.

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 provides clear usage context with concrete URL examples and defaults ('?start=2026-07-13&add=30', mode=ouvres default). It does not explicitly name when not to use it, but the context is sufficient for an agent to select it for French business-day arithmetic.

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