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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe, non-mutating operation. The description adds meaningful behavioral context beyond the annotations by disclosing the output contents: compatibility score (0-100), inter-aspect listings with strength ratings, harmonious vs. challenging counts, and relationship dynamics analysis. This is especially valuable because no output schema is provided, so the description is the only source of return semantics.

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 appropriately sized for a complex astrology tool, with the core purpose and key output benefits appearing in the first two sentences. The promotional closing sentences ('Perfect for dating apps...' and 'Based on professional astrological techniques') are somewhat optional but not misleading or bloated. Overall it is well-structured and front-loaded with the most decision-relevant information.

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?

Given the tool's complexity, nested input objects, and lack of an output schema, the description does a good job of covering the essential context: what is calculated, how, and what the response contains. The remaining gap is that it does not explicitly disambiguate from the closely related sibling post_astrology_compatibility_score or describe the exact output shape with field names, which could have improved completion for an agent. Still, it is sufficient for a strong first pass.

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 description does not explain individual parameter formats or expectations; it relies on the input schema to carry that load. The schema itself is rich, providing deep descriptions for person1/person2, lang, compact, and houseSystem. Since schema description coverage is around 60% and the description only adds context-level meaning ('between two natal charts') without parameter-specific help, it is not better than the baseline.

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 clearly states the tool calculates 'complete synastry (relationship compatibility) between two natal charts' using 'Western tropical astrology,' which is a specific verb, resource, and method. It also distinguishes itself from sibling tools like post_astrology_natal_chart (single chart) and post_astrology_compatibility_score (score-focused) by emphasizing detailed inter-chart aspect analysis and relationship dynamics. The title and description align tightly with the tool name.

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 clear use-case context, explicitly mentioning dating apps, matrimonial sites, relationship counseling tools, and astrology compatibility features. This tells an agent when this tool is relevant. However, it does not explicitly name sibling alternatives (e.g., post_astrology_compatibility_score for a simpler score, or post_astrology_composite for a merged chart) or state when not to use this tool, so it falls short of full explicit routing.

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