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 only the 'top-3 emphasized houses' output framing and the metadata tags ('Group: Comparisons', 'Cost: 50 credits (Tier 3)'), the cost note being genuinely useful. Nothing about determinism, error behavior, or truncation is added.

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?

Two tight sentences with the core operation front-loaded, followed by compact metadata. No filler, and the output expectation is stated up front.

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?

An output schema exists, so return values need no explanation, and annotations carry the safety profile; the cost/group tags cover billing context. What remains thin is routing among the numerous synastry variants, but for a two-chart read-only analysis the definition is otherwise complete enough to invoke correctly.

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 chart objects are richly documented in the schema itself, so the baseline is 3. The description adds no parameter detail beyond what 'chart1'/'chart2' already imply; 'fields' and 'precision' compact-mode parameters are explained only in the schema.

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: 'Locate each chart's personal planets in the partner's houses' plus the output shape ('top-3 emphasized houses on either side'). This clearly distinguishes it as a house-overlay analysis, though it never contrasts itself with close siblings like astroway_relational_synastry 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?

The description says what the tool computes but gives no when-to-use guidance, no prerequisites, and no alternatives among the many synastry siblings. An agent must infer that this is the 'house overlay' flavour of synastry purely from the name.

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