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

Annotations already carry the safety profile (readOnlyHint=true, destructiveHint=false) and the description is consistent with them ('Retrieve'). The description adds modest context about response contents (opening day sign and composed reading) but does not disclose behavior on invalid input, response limits, or any other operational traits. With annotations present, this is adequate but not rich.

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 sentences with zero filler. The first sentence front-loads the action and return contents; the second adds use cases. Every word earns its place.

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 simple tool with one required parameter, exhaustive schema documentation, and safety annotations, the description covers purpose, return contents, and use cases. It could additionally note that the plural trecenas endpoint covers the full set of twenty, but nothing essential is missing for correct invocation.

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%, so the schema already documents number (1-20 with opening-sign examples like 'Trecena 1 opens on 1 Cipactli'), lang (enum with English fallback behavior), and compact (columnar shape and token savings). The description's 'by number' adds no meaning beyond the schema, so it lands at the baseline 3.

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: 'Retrieve one of the twenty tonalpohualli trecenas by number,' and names the return contents ('the day sign it opens on and a composed reading of the period'). The singular 'one of the twenty... by number' distinguishes it from the plural sibling get_mesoamerican_astrology_aztec_trecenas and from the Mayan counterpart get_mesoamerican_astrology_mayan_trecenas_number.

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?

Provides explicit use cases: 'Built for period detail pages and for apps that show which thirteen day block a date falls in.' This is clear context for when to invoke the tool, but it stops short of naming alternatives or stating when not to use it, such as redirecting to the list sibling when all twenty trecenas are needed.

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