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

The annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavioral context: POST /v1/mayan/compatibility, a 10-credit Tier 1 cost, the required inputs, and that the output is a bounded 0-100 score, which tells an agent how to interpret and budget the call.

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 core sentence is front-loaded and dense with meaning, and the bracketed metadata lines are terse. The [Required: person1, person2] line largely duplicates the schema's required array, which is the only real 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?

An output schema exists, so return values need not be explained beyond the 0-100 score note, and cost/credit tier plus endpoint are disclosed. The remaining gap is how the two person date inputs feed the Tzolkin calculation, which is minor for a two-parameter compatibility call.

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 50%: fields and precision are documented in the schema, while person1 and person2 are undocumented nested objects. The description only restates 'Required: person1, person2' and hints that the computation derives from birth dates via Tzolkin name/tone, but never states that each person needs a YYYY-MM-DD date, leaving the half-documented parameters unimproved.

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 states a specific resource and computation: pair compatibility derived from Tzolkin name plus tone alignment and elemental/directional affinity, returning a 0-100 score. That clearly separates it from single-person siblings like astroway_mayan_tzolkin or astroway_mayan_full, though it never names those siblings explicitly.

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: the tool takes two people, so an agent can infer it is for comparing two individuals rather than generating one chart. There is no explicit when-to-use or when-not-to-use guidance, and no routing to alternatives such as astroway_mayan_full for a single person's full Mayan profile.

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