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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, but the description adds genuinely new behavioral context: deterministic JPL DE440 computation with no LLM, a meta.result_sha256 for verification, $0.06 pricing, and x402/MPP payment. It stops short of covering error behavior or rate limits beyond the free-call note.

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 long but front-loaded with the payload contents before determinism and pricing details, and almost every clause carries information. Minor marketing padding ('Everything a natal reading needs') and some repetition of schema-listed house systems keep it from a 5.

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 complex 9-parameter tool with no output schema, the description usefully enumerates return contents (positions, cusps, aspects with applying/separating state, element/modality balance, sect, Part of Fortune) and flags the result hash. It leaves out any mention of warnings (e.g. TIME_UNKNOWN is only in the schema) and error handling, but is otherwise sufficient.

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 89%, so the schema already documents all 9 parameters including defaults, enums, and the nested options object. The description restates defaults (Placidus, orbs, aspects) and the 11 house systems but adds no syntax or constraint detail beyond what the schema provides, so the baseline 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 and enumerates its contents precisely ('planets in signs and houses, ascendant, MC, 11 house systems, aspects, summary'), so an agent knows exactly what it computes. It is labeled 'Western' against Vedic siblings like kundli/kundli_full, but it never explicitly names a sibling or routes between them, so differentiation stays implicit 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?

Usage is only implied: 'Everything a natal reading needs' signals that this is the comprehensive chart call, but there is no when-to-use/when-not statement and no comparison to siblings such as planet_positions or aspects. The pricing/payment sentences describe access mechanics, not tool selection.

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