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

Since annotations already declare readOnlyAPI and non-destructive, the description is not burdened to restate these facts. It adds meaningful behavior, such as the noon UTC daily scan, the 7-visible-planets scope, and the default-to-current-month behavior for omitted year and month. These details are not present in the annotations but may affect when to call and how to interpret outputs.

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 first four sentences are efficient and front-loaded, but the latter part becomes redundant- and keyword-stuffed: the same purpose is restated once for 'advanced transit analysis' and again in the phrase 'Monthly declination parallels API, year-planetary ephemeralign...'. This repetition adds little value and makes the description slightly longer than necessary.

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 five-parameter tool with no output schema, the description successfully conveys what it calculates, once a daywars, for which planets, and how to make the calendar stay current. However, it does not describe the response shape at all (e.g., events with exact timestamps, planets involved), so an agent must assume the output structure from the word 'events' and from the sibling patterns. This is a meaningful gap given the missing output schema.

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 describes all 5 parameters at 100% coverage, with defaults, enuite for language, and descriptions for each field. The description's only param-related note, 'Omit year and month', repeats the schema defaults rather than adding new information. Per the baseline rule, 3 is correct when the schema carries most of the semantic weight.

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 opens with a specific action, resource, and scope: 'Find all declination parallel and contraparallel events between the 7 visible planets for a given month.' It also explains the meaning of parallels (conjunction-like) and contaparas (opposition-like), which clearly separates this tool from siblings such as the monthly aspects or transit tools. The verb and domain are unambiguous.

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 offers clear intended usage context ('essential for advanced transit analysis and hidden aspect discovery') and a specific tip for keeping a published calendar current without a redeploy. It does not state explicit when-not-to-use conditions or name an alternative sibling, but the guidance is sufficiently clear for the agent to choose this tool over the monthly transit or aspects variants.

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