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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false, idempotentHint=true), so the bar is lower. The description still adds real value by disclosing the default behavior (full) and the exact contents of each return mode, which is otherwise unavailable since there is no output schema. It says nothing about failure modes or how partial data is surfaced, keeping it below a 5.

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?

Front-loads the core statement ("A natal chart from birth data") and then answers the two questions an agent actually has: what does each mode return, and when do I call this. The parenthetical inventory of the full return is dense but each item earns its place. It is a long single breath before the usage sentence, which slightly hurts scannability.

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?

For a nested-object tool with no output schema, the description is nearly sufficient: it explains the return modes, scope and calling conditions. It leaves unstated how errors or out-of-range/unknown-time input surface to the caller, though the schema itself documents the null-time behavior.

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 coverage is 0% and the enum for "part" carries no per-value documentation, so the description carries the full burden. It defines every enum value in concrete terms (full, short, planets, angles, houses, aspects, elements, fixed-stars) and states the default, which is exactly the compensation the schema lacks.

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 resource (a natal chart computed from birth data) and precisely enumerates what the tool returns for each mode. It does not name a sibling such as synastry or transits to differentiate itself, so the boundary with those tools must be inferred from subject matter rather than stated.

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?

"Use it whenever the user gives a birth date, time and place and asks about their chart, signs, houses or aspects, and before interpreting anything" is an explicit trigger condition, and it adds a useful efficiency hint (part=short suffices for Sun, Moon and rising). No explicit when-not or named alternative tool is given, so it stops short of a 5.

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