render_natal_chart

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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real context: output is a 720px PNG surfaced to the user, and it renders an already-existing chart. It does not say what happens if no chart exists yet or how errors surface, so not a 5.

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 sentences, no filler. The output form and size come first, then the input requirements and the one genuinely non-obvious rule (fold handling).

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 read-only render tool with no output schema, the description supplies the output artifact (PNG, 720px, shown to user), the required inputs, and the house-system choice. That is enough for an agent 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 description coverage is 0% across 8 params, so the description has to compensate. It covers location_id, the date/time inputs collectively, house_system options (placidus or whole_sign), and explains fold via the DST ambiguity warning. The y/m/d/h/min split is left to obvious naming.

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: 'Render the existing natal chart wheel as a 720px PNG'. Makes clear it produces an image shown to the user, which distinguishes it from the calculate_* siblings in the 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?

Gives prerequisites (exact birth date, local time, selected location_id) and a decision rule for ambiguous civil time ('ask ... instead of guessing fold'). It does not explicitly route to a sibling such as calculate_natal_chart, which keeps it 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.