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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is covered. The description adds operationally useful context beyond that: the credit cost (10 credits, Tier 1), the concrete endpoint, and a summary of the returned components. It does not cover timezone handling or rate limits, keeping it out of 5 territory.

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?

The prose is a single tight sentence, front-loaded with the calendar and the return shape, followed by compact bracketed metadata lines. Every line carries information (group, endpoint, required param, cost). Slightly dense metadata formatting but no wasted sentences.

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?

An output schema exists, so the description need not detail return values, yet it still summarizes the payload. Combined with the endpoint, required parameter and cost disclosure, an agent has everything needed to invoke this simple single-date lookup correctly; the only real gap is tzolkin-vs-sibling routing, which belongs to the usage dimension.

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 67%: 'fields' and 'precision' carry full descriptions while 'date' has only a regex pattern and no prose. The description restates that date is required and adds nothing about the expected date format, timezone, or how fields/precision interact with this endpoint. That is the baseline expected when the schema does most of the work.

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-free but concrete resource: it returns a Tzolkin day sign composed of a 1-13 number, one of 20 day names, plus element, direction and keyword. That is far more specific than a tautology. However, it never distinguishes itself from the many Mayan siblings (haab, long_count, calendar_round, dreamspell, full), so an agent cannot tell from the description alone why it should pick tzolkin over mayan_full.

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?

There is no when-to-use statement, no exclusion, and no named alternative. The bracket metadata notes 'Required: date' and the cost tier, but neither is guidance about choosing this tool versus the other Mayan calendar endpoints. 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.