Ephemeris Range

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

Annotations already declare readOnly/idempotent/non-destructive, so the description's job is to add context — which it does: a minimum step of 0.01 days, hard range ceilings, and a cost of 100 credits (Tier 4). Disclosing cost is genuinely useful pre-invocation information. It does not say what happens when a range exceeds the cap (error vs. truncation).

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?

Two tight sentences with the range/step constraint front-loaded, followed by a compact bracketed block carrying group, endpoint, required params, and cost. Every line earns its place; only the endpoint line is arguably redundant for an agent that does not make raw HTTP calls.

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?

Output schema exists, so return fields need no explanation, and the description covers the operational envelope an agent needs: valid input ranges, step floor, optional filtering, and credit cost. The remaining gap is date/time semantics (which timezone or ephemeris frame the positions use), which matters for a precision-heavy astronomy call.

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 0% across 4 parameters, so the description must compensate. It adds real meaning for stepDays (0.01-day minimum plus the range coupling), but startDate/endDate get only 'required' with format left to the schema pattern, and planetIds is named without explaining accepted ID values or the 32-item cap.

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 ('Return planet positions') plus the scoping dimension ('for a date range'), which implicitly separates it from point-in-time tools like astroway_western_planets and from streaming siblings. It stops short of naming a sibling explicitly, so it lands just under the top mark.

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 step-size and range caps (1 year for sub-day steps, 5 years otherwise) tell the agent when a call is valid, and the optional planetIds filter is flagged as optional. But there is no explicit guidance on when to choose this over astroway_western_planets, astroway_stream_positions, or astroway_calendar_ingresses, so selection still requires inference.

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