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

Annotations already declare readOnly/idempotent/non-destructive and open-world, so the safety profile is covered. The description adds one genuinely useful behavioral fact: the results are computed offline from python-holidays, i.e. a deterministic bundled dataset rather than a live service. However, this also sits awkwardly against openWorldHint=true, and nothing is said about data freshness or coverage 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?

It is compact and front-loads the topic, with no filler. But the capabilities are a comma-spliced list without verbs or grouping, and the trailing 'Offline, python-holidays.' reads as implementation shorthand rather than agent-facing guidance. Dense but imperfectly structured.

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 an 8-parameter, zero-required, multi-mode tool with no output schema, the description lists what can be asked but not how the parameters compose, what the defaults produce, or what a response looks like. It is enough to know the tool exists and roughly what it answers, but not enough to call it confidently in mode-heavy cases.

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 75% and two parameters (list_year, add_business_days) carry no description at all; the description's phrases 'a year's holidays' and 'date + N business days' partially compensate by hinting at those two. It still does not explain the mode structure — that 'market' replaces 'country', or that 'until' and 'add_business_days' are alternative modes — leaving valid combinations ambiguous. Baseline 3 for high coverage with marginal added meaning.

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 enumerates the concrete capabilities (is-this-a-working-day, holiday name, next/previous business day, date + N, business days between dates, a year's holidays) on a clearly named resource: business days/holidays. An agent can tell immediately what domain the tool covers. There is no explicit verb and no sibling differentiation, but the siblings (company_lookup, fx_rate, vat_check, etc.) are unrelated, so distinction is not needed.

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?

Usage is only implied through the list of use cases; there is no explicit when-to-use / when-not statement and no guidance on selecting modes. Critically, the description never maps a use case to the parameter set that triggers it (e.g. 'a year's holidays' -> list_year, 'date + N' -> add_business_days), so the agent must infer mode selection. Implied usage with clear gaps = 3.

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