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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so safety needs no restating. The description adds two pieces of genuinely non-structured information: the 1-credit cost and the lunar-calendar boundary rule (year starts at Chinese New Year, not January 1st), which materially affects interpretation of results. No output format context is offered, but an output schema exists so that is not a serious gap.

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?

Three short sentences, front-loaded with the return value and then the key nuance. The leading 'Chinese Zodiac:' label merely repeats the tool name and could be dropped, but otherwise there is little waste.

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?

With an output schema present, the description need not describe return values, and it covers the calendar nuance and cost well. But for a tool with two optional, unrequired parameters and no usage rules, the definition leaves the agent guessing about the animal parameter and the date/animal interaction, which is an actionable gap.

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%, so both parameters are already documented, which sets the baseline at 3. The description clarifies how the date is interpreted (lunar-year boundary), which does add some meaning beyond the raw format string. However, it never explains the animal parameter's role or what happens when both date and animal are supplied, leaving the most ambiguous part of the schema unaddressed.

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: returns zodiac animal, element, and characteristics for a birth date. This clearly distinguishes it from calendar-adjacent siblings like MayanCalendar or Horoscope without needing to name them. The only blemish is the redundant restatement of the tool name at the start of the sentence.

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 by 'for any birth date'; there is no explicit statement of when to use this versus alternatives such as MayanCalendar, Horoscope, or Birthstones, and no guidance on prerequisites. Nothing tells the agent how the optional date and animal parameters relate or when to prefer one over the other.

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