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

Annotations cover safety (readOnly, idempotent, non-open-world), but the description adds substantial traits beyond them: JPL DE440 as the ephemeris source, determinism with no LLM, a verifiable meta.result_sha256 on every result, the 1800-2200 validity window, and the cost model ($0.01/call, x402 or MPP, first 3 free). These are exactly the operational facts an agent needs before invoking a paid, verifiable tool.

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 dense sentences, front-loaded with what is computed before moving to source, location handling, determinism and pricing. The pricing/payment detail is lengthy but earns its place for an agent budgeting calls; the celestial-body enumeration is somewhat redundant with the schema's points enum.

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 burden well, listing sign, degree, element, modality, daily speed, retrograde status and the result hash. Combined with the data range, determinism guarantee and cost, an agent has everything needed to call it correctly.

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 89%, so the schema already documents most parameters. The description still adds meaning beyond it by clarifying that location inputs are optional and serve only to interpret a local time, which disambiguates latitude/longitude/timezone behavior. It does not add detail on the options object's aspects, orbs or house_system parameters.

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+resource: computes tropical/sidereal longitudes, latitudes, speeds and retrograde flags for Sun..Pluto, nodes and Lilith. The scope (geocentric apparent positions, 1800-2200) clearly separates it from natal_chart, transits and aspects siblings.

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?

The description explains that location is optional and only used to interpret a local time, which implies usage context, but it never states when to prefer this tool over siblings like natal_chart, transits or aspects, nor any exclusions. Usage is left to inference from the scope statement.

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