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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so safety needs no restating. The description adds real domain behavior: the exact period lengths (Ketu 7/3, Venus 20/3, Sun 2...), the 40-year cycle, and that it returns the running cycle of 9 mahadashas, which is context the annotations cannot supply.

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-loads the definition, then the use case, then the return shape. The planet sequence and period fractions are somewhat dense but are the tool's core semantics; no filler sentences.

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 structure needn't be explained, and the params are fully documented. The description covers what it computes, how it differs from Vimshottari, and its timing niche, leaving only sibling-level routing to inference.

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% (body, fields, precision all documented, including the compact-mode dotted paths and precision rounding). The description adds no parameter-level detail, so the baseline 3 is correct.

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 precisely what is computed (Tribhagi Mahadasha periods) and anchors it against the sibling it most resembles: a 1/3-scale variant of Vimshottari with the same 9-planet sequence and nakshatra rule. An agent can distinguish it from vimshottari_maha and from the tribhagi_antar/pratyantar/prana/sookshma levels without opening a 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?

"Useful when finer-grain timing is needed within a Vimshottari-equivalent span" gives a clear selection rationale versus the Vimshottari baseline. It stops short of naming the finer tribhagi siblings or stating when-not to use it, so it is context rather than full routing.

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