render_lunar_return_chart

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

Annotations already declare read-only, idempotent, non-destructive, closed-world. The description adds the output format and size (720px PNG wheel) and the fact that it is surfaced to the user, which matters because there is no output schema. It does not mention whether the chart is cached or how it is returned (URL, base64, attachment), which is a remaining gap.

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 short sentences, front-loaded with the verb and artifact, second sentence carrying the parameter pointer. Nothing is wasted.

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 and 12 undocumented nullable parameters, the description leans entirely on a sibling reference for input semantics and says nothing about the return value shape. For a rendering tool whose whole product is a binary artifact, that leaves an agent guessing how the PNG comes back.

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?

All 12 parameters have 0% schema description coverage, so the schema itself explains nothing. 'Same inputs as calculate_lunar_return' is meaningful compensation — it tells the agent where the semantics live — but it forces a cross-tool lookup and gives no hint about the day/hour/fold vs target_day/target_year/target_month split.

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 (render), a specific resource (lunar return chart), and the artifact form (720px PNG wheel shown to the user). This cleanly distinguishes it from calculate_lunar_return and from render_solar_return_chart/render_natal_chart in the sibling list.

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?

'shown to the user' implies this is the display step that follows computation, and the explicit reference to calculate_lunar_return gives the agent a routing rule between compute and render. No explicit exclusion or prerequisite (e.g., must compute first) is stated, so it stops short of a 5.

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