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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine behavioral context — the default targetDate is today UTC, the result is exactly 9 ADs, and the cost line flags 20 credits (Tier 2) — but says nothing about output shape or temporal bounds.

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?

Three tight sentences, purpose first, formula last, followed by compact group/endpoint/cost metadata. Every line carries information; the formula is marginally decorative for tool selection but justifies the AD length semantics.

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?

With an output schema present, return formatting need not be explained, and the input schema is unusually rich. The description supplies the one thing the schema omits (targetDate default) and the computation semantics, leaving only sibling routing as a gap.

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% and the birth-data sub-schema is exhaustively documented, so the baseline is 3. The description earns an extra point by supplying the targetDate default ('today UTC'), which the schema itself does not declare.

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, well-defined output: it identifies the active Mahadasha at targetDate and returns the 9 Antardashas covering it, plus the AD-length formula. The term 'Antardasha (sub-period)' is defined inline, which separates it from the maha/pratyantar/prana/sookshma siblings by level. It does not, however, name any sibling explicitly for contrast.

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 implied by the period hierarchy (you want the second-level breakdown inside the running MD) and the description clarifies the default target date, but it never states when to choose this over vimshottari_maha, vimshottari_pratyantar, or the parallel Ashtottari/Yogini/Chara families.

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