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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds value beyond them by disclosing the computed output shape (aspects with orbs, bidirectional house overlays, per-sphere score) and the '(API Pro)' tier requirement, which an agent should surface before invoking.

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 sentences, zero padding, and the output contents are front-loaded ahead of the usage condition. Every clause earns its place.

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 correctly takes on the burden of describing the return contents, and it does so concretely. Combined with the well-documented nested birth-data fields, an agent has enough to call it correctly; only the personA/personB role distinction is left implicit.

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 schema coverage is 0%, so the two person objects carry no description of their own; the description compensates only loosely by saying both people must supply birth data. It adds no semantics about what distinguishes personA from personB (e.g. directionality of overlays), though the nested field descriptions do the heavier lifting.

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 operation (two charts compared) and enumerates the concrete outputs: inter-chart aspects with orbs, house overlays both ways, and a score per life sphere. This clearly separates it from the single-chart sibling natal_chart without the agent needing to open either schema.

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?

Gives an explicit trigger: 'Use it when the user asks about compatibility or a relationship and gives birth data for both people.' That covers the key precondition (two people's birth data) but names no alternative sibling for the near-miss case, e.g. when only one person's data is available.

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