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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds genuinely new context: credit cost and tier ('20 credits (Tier 2)'), the transport endpoint, and the required-input set — real operational context that annotations do not carry.

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 core definition, then compact bracketed metadata (group, endpoint, required, cost). It is dense but every line carries information; no filler prose.

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 explanation is not required, though the description helpfully names the three returned fields. For a 15-parameter tool with 33% schema coverage and many near-identical panchang siblings, the description is minimally adequate but leaves parameter and sibling-selection gaps.

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 only 33% across 15 parameters, so the description is expected to compensate and largely does not. It restates the four required fields already marked required in the schema, but says nothing about zodiacType, houseSystem, ayanamsaId, cosmogram, city or name, leaving a large documentation gap.

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 gives a precise verb-adjacent definition: 'Lunar day (1-30): Moon-Sun elongation / 12°', and names the concrete outputs (paksha, tithi name, % complete). An agent knows exactly what computation this performs. It does not, however, distinguish it from sibling panchang tools (panchang_full, nakshatra_of_day, karana, yoga), several of which also touch tithi-adjacent daily values.

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?

Prerequisites are explicit ('Required: date, time, latitude, longitude') and the endpoint/cost framing implies when the call is warranted. But there is no 'use this vs panchang_full' guidance, and no exclusions, so usage is only implied by the definition of a tithi.

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