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

With no annotations, the description carries the burden. It usefully discloses that evaluation happens in the calendar's local time zone and that upcoming holidays are included in the answer, which is real behavioral context for a read query. It does not describe the response shape or what 'upcoming' spans, so disclosure is partial.

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?

Two short sentences, zero filler, with the core question front-loaded and the time-zone qualifier immediately after. Nothing needs trimming.

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 one-parameter read-only query with no output schema, the description covers what is asked, the time-zone semantics, and that holidays appear in the result. The main gap is disambiguation from is_business_day, which the description never addresses.

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 the single 'calendar' parameter is fully documented in the schema with id examples (us-fed, xnys, de). The description adds no syntax or format detail beyond that, 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?

The description states a specific question it answers ('Is today a business day') on a named resource (this calendar), scoped to today rather than an arbitrary date. However, it never distinguishes itself from the sibling is_business_day, leaving the agent to guess which one to call for the 'today' case.

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 implied by the word 'today' and by the time-zone note, but there is no explicit when-to-use statement and no named alternative (is_business_day, add_business_days, list_holidays) to route the agent. The agent must infer the choice from the sibling names alone.

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