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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful behavior beyond that: with timeUnknown the cross-aspects are still returned while that partner's houses, angles and sect come back null, and it discloses the 50-credit Tier 3 cost.

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 purpose and the timeUnknown caveat are front-loaded in two tight sentences, and the bracketed group/cost metadata is compact. Slight redundancy with the schema's own timeUnknown text keeps it from a 5.

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 four-parameter, nested-object tool with a full output schema present, the description covers the operation and its most important edge case. The main gap is sibling differentiation, since several relational tools overlap in apparent function.

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 both chart objects carry their own detailed descriptions (timezone, ayanamsa, timezoneOffset, timeUnknown), so the schema does the heavy lifting. The description's timeUnknown sentence largely restates what the chart1/chart2 schema already says, adding no syntax or format detail beyond it.

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 gives a specific verb+resource ('Calculate cross-chart aspects between two natal charts') and a use case ('relationship analysis'), which separates it from composite/davison siblings that derive a single merged chart. It does not, however, distinguish itself from the very similarly named astroway_relational_synastry_aspect_grid, which an agent could easily confuse with it.

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?

There is no statement of when to use this tool versus astroway_relational_synastry_aspect_grid, astroway_relational_match_score, or the composite/davison alternatives. The timeUnknown note describes an input edge case rather than usage routing, so an agent gets no explicit selection guidance.

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