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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered. The description adds the aggregation behavior and the credit tier (50 credits, Tier 3), which is genuinely useful, but it largely enumerates return contents that the output schema already documents, so the net addition is moderate.

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?

Front-loads the aggregate purpose and the return payload, then the routing guidance, with little waste. The trailing 'Same TwoChart in…' is truncated mid-sentence, which slightly hurts structure but the delivered content is efficient.

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 read-only aggregate with a full output schema and thoroughly documented nested input objects, the description covers what an agent needs: what it computes, why to prefer it over composing siblings, and the cost. No major gap remains, though the truncated final sentence leaves a small hole.

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 100% and the nested chart1/chart2 objects are richly documented in-schema (timezone handling, houseSystem letters, rejected short forms). The description says nothing about the parameters, so it adds no meaning beyond the schema. 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?

States a specific verb and resource ('one-call dating-compatibility aggregate over the synastry engine') and enumerates exactly what it returns: overall score, label, harmony/tension, attraction score, influential cross-aspects, and green/red flags. This clearly distinguishes it from narrower siblings like astroway_relational_synastry_attraction_score or astroway_relational_synastry_aspect_grid.

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?

Explicitly frames the use case and the alternative: 'Built for dating apps that want a single call instead of synastry + attraction + their own flag logic.' That routes the agent between this tool and composing the narrower siblings. It lacks an explicit when-not-to-use statement or named sibling tools, keeping it below a 5.

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