ephemeris_natal_chart

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

Annotations already mark the tool as readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds substantial behavioral context beyond that: credit cost per call, extra credits for visual, automatic inclusion of asteroids, routing of flags to underlying config, and that the result is raw JSON (with SVG embedded when include_visual=true). No contradictions with annotations.

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 description is multi-paragraph but every sentence earns its place: it covers purpose, return contents, format recommendation, credit cost, an example, and sibling alternatives. It is front-loaded with the core purpose. Some minor redundancy exists (the return list is mentioned twice), but overall it is efficient and well-structured.

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?

Given 10 parameters, a nested object, and no output schema, the description is remarkably complete. It explains credit costs, how to handle timezone ambiguities, what is automatically included, how to use format='llm', and points to sibling tools for alternatives. It leaves no obvious gaps for correct invocation and interpretation.

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 baseline is 3. The description adds valuable clarification beyond the schema: it explains the purpose of format='llm', gives a concrete datetime/timezone example with Chicago, and warns that latitude should not be recalled from memory. This extra context helps correct parameter usage, warranting a slight bump.

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 opens with a specific verb ('Calculate a full natal (birth) chart') and clearly states what it returns (planetary positions, house cusps, aspects, chart patterns). It differentiates itself from the sibling explore_natal_chart by explicitly directing user-facing visual charts there, and also names standalone endpoints for fixed stars and Arabic parts.

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?

Provides explicit guidance on when to use this tool versus alternatives: 'For a user-facing visual chart, use explore_natal_chart instead', and for standalone fixed-stars/hermetic lots payloads, recommends /ephemeris/fixed-stars and /ephemeris/hermetic-lots. It also recommends format='llm' for token-efficient interpretation and tells users to resolve coordinates with location_search.

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