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

Annotations already cover read-only, idempotent, non-destructive behavior, so the bar is lower. The description adds two genuinely useful behavioral facts beyond them: omitting birth time degrades output (no houses, Ascendant, MC), and birth data is not stored or logged. It says nothing about failure modes such as unresolvable place names or geocoding limits.

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 output inventory, then usage, then required inputs, then the privacy note — a sensible order with little waste. The opening sentence is long and list-heavy, but every clause carries information about what is returned.

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 no output schema, the description carries the return-value explanation and does so thoroughly, and it flags the degraded mode when birth_time is absent. Minor gaps remain around geocoding failure behavior and error reporting for an eight-parameter tool.

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%, so the schema already documents all eight parameters including defaults, ranges, and the place-vs-coordinates fallback. The description only restates the priority ('birth date, the place (or coordinates) and ideally the birth time') without adding format or edge-case detail beyond the schema. Baseline 3 applies.

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 ('Calculates a natal (birth) chart') and enumerates exactly what it returns: Sun/Moon/planet positions, angles, house cusps, and aspects with orbs. The mention of the Swiss Ephemeris and tropical features (Ascendant, MC, Koch/Placidus houses) implicitly separates it from the Vedic sibling, but no sibling is ever named explicitly.

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?

Gives a clear trigger: 'use it when someone asks for their birth chart or about their placements,' and states the input prerequisites. It does not address when to prefer vedic_chart, sky_today, or transits_today, so an agent must infer the boundary from the tool names.

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