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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so safety and determinism are covered structurally. The description adds the output contents and a hint at tier gating, but says nothing about what happens when a birth time is missing or how the computation degrades.

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?

A single front-loaded sentence that enumerates the three deliverables without padding. It is efficient, though the parenthetical tier tag is cryptic.

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 usefully sketches the return shape (aspects, overlays, sphere scores), which is the most important gap it could fill. It still omits parameter intent and any behavior around unknown birth times, leaving the complex nested input under-explained.

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?

Top-level parameter coverage is 0%: neither personA nor personB is described, so the two-object contract is left to the nested schema. The description adds no parameter meaning at all, and it does not explain the symmetry or ordering requirements of the two birth-data objects.

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 action (compare two charts) and names three concrete outputs: inter-chart aspects with orbs, house overlays both ways, and a per-sphere score. This distinguishes it from the single-chart natal_chart sibling, though it never names that alternative explicitly.

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 when-to-use guidance, no comparison against natal_chart or transits, and no note on prerequisites such as the API Pro tier except the terse '(API Pro)' tag. The user must infer that this is the two-person compatibility tool 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.