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

Annotations already cover safety and idempotency (readOnlyHint, idempotentHint, openWorldHint=false), and the description adds substantive context beyond them: deterministic computation via JPL DE440 with no LLM, a verifiable meta.result_sha256 on every result, a $0.12 per-call price, the REST endpoint, and x402/MPP payment plus 3 free calls. It does not discuss latency, failure modes, or rate limits beyond the free tier.

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?

Three sentences, data content front-loaded, no filler. The pricing/endpoint sentence is longer than needed for a tool description but is legitimately useful invocation context for an agent, so it earns its place on balance.

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 return-value burden well: it names the aspect/overlay/composite payloads, the counts, and the result hash. Combined with the determinism and cost disclosures, an agent can call it correctly; only error/edge-case behavior is undocumented.

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?

Reported schema description coverage is 0% at the parameter level, so the description is expected to compensate, yet it explains no parameter — time_basis, ambiguous_time, orbs, points, zodiac, and house_system are left entirely to the nested schema. Terms like 'with orbs' hint at the orbs control but add no syntax or defaults.

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 verb+resource (relationship comparison of two natal charts) and enumerates exactly what is produced: cross-aspects with orbs, mutual house overlays, harmonious/challenging counts, and composite midpoints. This cleanly separates it from single-chart siblings like natal_chart and aspects.

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 requirement of two birth datetimes implies the two-person scenario, but the description never explicitly states when to choose this over natal_chart, aspects, or gun_milan, nor any exclusion. Usage is inferable from the resource, not from stated guidance.

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