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

Annotations already declare readOnly=true, idempotent=true, destructive=false, so safety is covered. The description adds genuinely useful non-annotation context: the credit cost model, the free sandbox key, and the determinism guarantee. It stops short of describing the Fagan–Bradley mean-without-nutation caveat framing returned fields, but the added billing and determinism notes are valuable.

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 use-case, then system list, cost, determinism, and an example—each sentence earns its place. Slightly redundant phrasing between the first two lines ('at a moment' repeated), but overall tight and well-ordered.

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 single-parameter, read-only tool with a fully documented schema, output schema present, and annotations covering the safety profile, the description covers use-case, supported systems, pricing, and determinism. Nothing an agent needs to invoke it correctly is missing.

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 100%, so the datetime parameter's format, range, and refusal behavior are already fully documented in the schema. The description's example argument adds a small amount of convenience but no meaning beyond the schema, so the baseline of 3 is appropriate.

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: retrieve an ayanamsa value at a moment, naming the four supported systems (Lahiri, Raman, Krishnamurti, Fagan–Bradley). This distinguishes it clearly from siblings like get_ephemeris_positions, get_ephemeris_angles, and get_ephemeris_series, which return different quantities.

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?

The opening 'Use this when you need an ayanamsa value ... at a moment' gives a clear triggering condition and names the acceptable systems. It does not, however, explicitly distinguish itself from the other get_ephemeris_* siblings or state when a different ephemeris tool should be preferred.

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