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

With no annotations, the description must carry the behavioral burden. It discloses the default fallback (current year when date is omitted) and the exact time of day returned, but omits timezone assumptions, input date format expectations, and the format of the returned timestamp. For a simple pure function this is adequate but incomplete.

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?

One sentence, front-loaded with the tool's name and action, with zero wasted words. The default behavior is stated compactly without burying the main purpose.

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 single-optional-parameter pure function with no output schema, the description covers the core operation and default. However, it leaves out important details an agent needs: accepted date formats, timezone of the returned timestamp, and the timestamp's numeric/string format.

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 only says 'Date to process', which is vague. The description adds meaningful semantics: the parameter is optional and defaults to the current year, clarifying behavior beyond the schema. Date format specifics remain unstated.

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 ('Return') and resource ('end-of-year timestamp (Dec 31 23:59:59)'), making the operation immediately clear. It semantically distinguishes itself from year-start and month-end siblings, but doesn't explicitly name or route away from them.

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 default behavior ('current year if no date provided') is useful, but there is no explicit when-to-use guidance, no mention of when not to use it, and no pointer to alternatives like x402-year-start or x402-end-of-day. Usage is only implied by the tool name.

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