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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false; the description goes well beyond this by detailing the full return shape (cosmic_card_a/b, connections, overall_score, temporal_context), clarifying term equivalences ('Cosmic card = birth = life = sun via also_called'), and even providing ordering guidance for spread_pos. There is no contradiction with annotations.

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 front-loaded with usage conditions, followed by required parameters and a returns section. It is dense but organized, with only minor over-packaging such as nested parentheticals and comma-heavy enumerations. Every sentence contributes value, especially given the lack of an output schema, but the complexity prevents a perfect conciseness score.

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?

With no output schema, the description must fully explain return values, and it does: cosmic_card_a/b with get_date shape details, cultural names, planetary spread positions, temporal_context bands, and integration with Chinese zodiac and life paths. It also covers date format, required parameters, and the exact two-date scope, making the tool callable without external documentation.

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, with each parameter clearly described as 'Person A date' and 'Person B date' in YYYY-MM-DD format. The description only reinforces the 'exactly two people, not a roster' constraint already present in the schema, adding no new parameter-specific meaning. Baseline 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 leads with a specific verb+resource: 'comparing exactly two people by Gregorian date.' It explicitly distinguishes itself from siblings with 'NOT for one date ... → get_date' and 'names → get_name,' making the tool's scope immediately clear. The title 'Compatibility (two dates)' reinforces this.

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 provides explicit when-to-use and when-not-to-use guidance, naming sibling tools and their exact triggering cases. It also states the required parameters ('Requires date_a and date_b'), leaving no ambiguity about invocation conditions.

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