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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety and repeatability profile is fully covered by structured data. The description adds only 'with exact orbs and strength', hinting at output precision and detail level. It says nothing about how many aspects are returned, how the two datasets are paired, or what happens with low-precision birth times.

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 sentence with no filler, and the defining scope constraint ('between two people's birth charts') is front-loaded. It is efficient, though it is arguably sized too small for a tool taking two nested birth-data objects.

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 carries the burden of telling the agent what comes back; 'exact orbs and strength' does that only in outline. Combined with a 100%-documented nested schema and full annotations, it is enough to call the tool correctly, but thin for interpreting results. It never notes that omitted birth times degrade houses and angles despite the schema mentioning it per-field.

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 each nested field documents itself thoroughly (including the noon fallback when time is omitted). The description's phrase 'each one's planets to the other's' reinforces the asymmetric A-to-B mapping, but otherwise adds nothing the schema doesn't already carry. Baseline 3 applies.

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 states a specific resource — cross-aspects between two people's charts — and clarifies the mechanics ('each one's planets to the other's'), which distinguishes it in spirit from single-chart siblings like natal_chart and transits. It never names those siblings explicitly, so an agent must infer the boundary rather than being routed by name.

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 versus natal_chart, transits, or timing_events — the agent has to infer that synastry applies only when two birth datasets are being compared. No prerequisites, exclusions, or alternative routes are given.

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