Heliocentric Chart

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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely useful non-schema behavior: the Earth/Sun substitution and Moon exclusion, plus the endpoint and the 20-credit Tier 2 cost, which an agent needs for budgeting decisions. Return-value detail is left to the output schema, which exists.

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?

The distinguishing sentence comes first and the bracketed metadata lines are compact and scannable. Nothing is padded, though the required-parameter line duplicates what the schema already enforces, making it low-value text.

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?

The output schema relieves the description of explaining return values, and annotations cover safety. But for a 13-parameter tool with 23% schema coverage, the description leaves the agent without guidance on the sidereal/zodiac/house-system options that materially change the result.

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 only 23% across 13 parameters, so the description carries a heavy burden. It lists only the four required fields (date, time, latitude, longitude), which merely restates the schema's required array, and says nothing about the nine optional parameters such as timezone, ayanamsa, zodiacType, or houseSystem.

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?

Specific verb plus resource: 'Calculate heliocentric planetary positions (Sun-centered)'. The clarifying clause 'Earth replaces Sun; Moon is excluded' pins the exact astronomical convention, which meaningfully separates it from geocentric chart tools like astroway_western_chart. It does not explicitly name a sibling to avoid, so it stops short of 5.

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 guidance on when to choose heliocentric over the geocentric siblings, nor any prerequisite or exclusion stated. The only contextual hint is 'for a given birth moment', which describes input rather than selection criteria.

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