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

Annotations already declare readOnly, idempotent, closed-world behavior, so the safety profile is covered. The description adds real value beyond that: a supported date range of 1000–9999 and the fact that Zeller's working is shown in the response. It stops short of describing the exact return shape.

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 question, followed by scope, use cases, and output detail in one tight sentence. The trailing web-page URL is promotional filler but brief enough not to bury the substantive 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?

For a zero-required-parameter, single-input tool with rich read-only annotations and no output schema, the description supplies everything needed: what it computes, the valid range, and what the response includes. Nothing material 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% and the schema itself explains the empty-value default, so the baseline is already adequate. The description additionally constrains valid input to the years 1000–9999, which the schema's bare 'format: date' does not communicate.

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 ('Get the weekday for any date'), which is unambiguous about the single computation performed. It does not, however, name or contrast itself with adjacent siblings like date_difference_calculator or week_number_calculator, leaving the agent to infer the split.

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?

The examples ('birthdays, historic events, future plans') imply the intended contexts for use, which is useful framing. But there is no explicit when-not guidance and no routing to alternative date tools for adjacent needs.

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