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

Annotations already declare readOnly/idempotent/closed-world, and the description adds substantial context beyond them: determinism source (JPL DE440, no LLM), the meta.result_sha256 verification artifact, default ayanamsa (Lahiri) and the six available, plus pricing and a free-call allowance. That is real behavioral disclosure for a paid, verifiable computation.

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-loaded with the purpose and output content, then defaults and the lookup alternative. It is dense but the trailing pricing/endpoint sentence is commercial plumbing rather than tool-selection information, slightly diluting an otherwise efficient block.

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 10-parameter tool with nested options and no output schema, the description usefully enumerates returned content (pada, lord, gana, yoni, nadi, varna, janma nakshatra) and the default ayanamsa. It leaves the exact response shape and warning fields (e.g., TIME_UNKNOWN) to the schema, which is acceptable but not exhaustive.

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 90%, so the schema already documents nearly every parameter, including the enum options and the longitude_sidereal field. The description restates the ayanamsa default and the direct-lookup path but adds no format or syntax detail beyond the schema, 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?

States a specific verb+resource: 'Sidereal nakshatra, pada and lord of every graha' plus the janma nakshatra attributes and the 27 lunar mansions across 9 grahas. An agent can distinguish this nakshatra-focused tool from generic chart siblings like kundli or planet_positions without opening the 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 a concrete alternative input mode: 'Or pass longitude_sidereal for a direct lookup,' which tells the agent it can bypass date/time entirely. However, it never states when to prefer this over siblings such as planet_positions or kundli for related calculations, so routing guidance is partial.

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