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

Annotations already indicate readOnlyHint=true and destructiveHint=false. The description adds meaningful behavioral context by disclosing what each returned entry contains: the period number, the opening day sign, and a composed reading. This is valuable because no output schema exists to document the response 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?

The description is three tight sentences: it introduces the resource, explains the response contents, and states the target use cases. There is no filler, and the core purpose is front-loaded in the first sentence.

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 read-only list endpoint with no output schema, the description adequately explains what the tool returns and who it is for. It could go further by mentioning pagination behavior or pointing to the single-trecena sibling, but the essential information needed to invoke it correctly is present.

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?

The input schema has 100% description coverage for all four parameters (lang, limit, offset, compact), so the schema fully carries parameter documentation. The description does not restate or deepen parameter semantics, so the baseline score of 3 is appropriate.

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?

The description names a specific verb and resource: 'Retrieve all twenty trecenas, the thirteen day periods the 260 day tonalpohualli divides into.' It also states exactly what each entry contains, and the 'all twenty' wording distinguishes it from the sibling get_mesoamerican_astrology_aztec_trecenas_number endpoint.

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 description clearly frames intended use: 'Built for Aztec calendar apps, energy period trackers and content planners that work in thirteen day blocks.' It gives strong context but does not explicitly name the alternative for retrieving a single trecena by number, so it lacks explicit when-not-to-use guidance.

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