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

Annotations already declare read-only, idempotent, non-open-world behavior, and the description adds real substance on top: 'No predictions, nothing stored', the approximation caveat for a missing birth time, and the conditional inclusion of houses/angles. These are exactly the behavioral facts an agent cannot infer from annotations or schema.

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?

Four dense sentences, front-loaded with what is computed and what is returned, followed by the conditional rules and the safety caveat. No filler sentences and nothing repeated from the schema.

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 carries the burden of describing the return contents (planets, aspects, interpretation, optional angles/houses) and the accuracy caveat. It is nearly complete, but says nothing about behavior when a birth_place cannot be resolved or matched ambiguously, which matters for a tool whose fallback path is latitude/longitude/timezone.

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 coverage is 100%, so the baseline is 3; the description earns above baseline by documenting the parameter interaction that governs output — birth_time plus birth_place are jointly required for Ascendant, Midheaven and houses, and time alone leaves the Moon approximate. It does not add format/syntax detail beyond the schema's examples, so it stops short of 5.

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 verb and resource ('Computes a real birth chart from astronomical positions (tropical zodiac)') and enumerates the actual deliverables (Sun–Pluto with sign/degree/retrograde, major aspects with orbs, short interpretation). This clearly separates it from siblings like get_sun_sign_reading (single-sign reading) and get_transits (time-based transits) without opening 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 explicit conditional context: Ascendant/Midheaven/Whole Sign houses appear only 'when birth time and place are both given', and without a time 'the Moon is flagged as approximate'. That is strong when-to-expect guidance, but it never names an alternative sibling (e.g. compare_charts for two people) or states when not to use this tool.

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