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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered by structured data. The description adds the genuinely useful behavioral fact that it is a static, chart-independent lookup, but says nothing further about response shape or size. Adequate but not rich given the low bar annotations set.

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 core sentence is information-dense and front-loaded with the resource, followed by the decisive "no chart needed" constraint. The bracketed cost/group tags are boilerplate but short. Nothing is padded, though the attribute enumeration is somewhat list-like rather than 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?

An output schema exists, so return-value description is not required, and the input schema fully documents both optional parameters. The description tells the agent what content to expect and that no chart input is needed, which is sufficient for a static reference tool. Only the missing sibling disambiguation keeps this below 5.

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% and the schema is largely self-documenting, so a baseline of 3 applies. Both parameters (fields, precision) are generic compact-mode controls already fully explained in the schema; the description adds no serialization or formatting guidance beyond it.

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 (the nine Navaratna gems) and enumerates the attributes it returns — graha, substitutes, weekday, finger, metals, weight in ratti/gram/carat, beeja mantra, japa count. It is clearly a reference-lookup tool rather than a computation. The only weakness is that it does not explicitly distinguish itself from the very similarly named sibling astroway_vedic_gemstones.

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?

"Static lookup, no chart needed" gives a real usage condition — an agent knows no birth data is required — which is meaningful context. However, it never names the closest alternative, astroway_vedic_gemstones (or reports_gemstone / esoteric_crystals), so the selection reasoning is left for the agent to infer from names alone.

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