ephemeris_midpoints

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

Annotations already indicate read-only behavior. The description adds value by detailing the return data (midpoint longitude, planets involved, any planet at the midpoint) and the credit cost. It does not contradict annotations and provides context beyond what structured fields offer.

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?

The description consists of two sentences: the first states the purpose and output concisely, the second states the credit cost. It is front-loaded and contains no redundant information.

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?

For a tool with 3 required parameters, full schema descriptions, and a readOnlyHint annotation, the description is sufficient. It explains what is calculated and returned, but lacking an output schema means the agent must infer the output format. However, the description is adequate for a simple read operation.

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?

Input schema coverage is 100% with descriptions for all parameters. The description does not add extra meaning beyond the schema; it mentions datetime and location but no additional format details or constraints.

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 clearly states it calculates midpoints between all planet pairs for a given date/time and location, and lists what is returned (midpoint longitude, planets involved, any planet at midpoint). This is a specific verb-resource pair that distinguishes it from sibling tools like ephemeris_aspect_check or ephemeris_planet_position.

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 implies usage for calculating planet midpoints but does not explicitly state when to use this tool versus alternatives (e.g., for aspects or single planet positions). No exclusions or alternative tool names are provided.

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