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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description adds genuine value by disclosing provenance ('NASA JPL data by Naelos Ephemeris'), which implies a deterministic calculation rather than an external live lookup, but it says nothing about accuracy limits, failed geocoding, or behavior when time is absent.

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, front-loaded with the deliverable and then a compact enumeration of contents. Every clause carries information; only the closing provenance sentence could arguably be trimmed, but it still earns its place by signaling determinism.

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 enumerates the return payload (planets, angles, retrogrades, aspects with orbs), which is the main thing an agent needs. It stops short of routing the agent to siblings or noting degraded results when time is omitted, but the schema covers the latter.

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%, so every parameter including the house_system enum and the time-omission caveat is already documented upstream. The description adds no parameter-level detail beyond what the schema provides, so the baseline of 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 names a specific resource (natal/birth chart) and enumerates exactly what it contains: planetary signs, degrees, houses, angles, retrogrades, and aspects with orbs. It is clear what the tool produces, but it never contrasts itself with sibling tools like planet_position or synastry, which also compute chart-derived data.

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?

Usage is only implied by the resource name — an agent can infer this is the tool for a full birth chart from birth data. There is no explicit statement of when to prefer it over planet_position or synastry, and no mention of prerequisites such as needing known birth time (a documented caveat only in the schema).

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