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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds the cost (10 credits, Tier 1) and the endpoint, which are genuinely useful operational facts, but says nothing about output format choice (svg vs json) or the credit being charged per render.

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 compact sentences carrying the core operation, followed by terse bracketed metadata. Front-loaded and free of filler, though the bracketed tags add length without much descriptive value.

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 an output schema present and 100% schema coverage, the description need not explain returns. However, for a rendering tool with an option-heavy schema (theme, size, labels, format) it omits any hint about output form or that a two-chart input pair is required, leaving the agent to infer from the schema.

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 100%, with rich prose on chart1/chart2, timezone, houseSystem, theme and fields, so the schema does the heavy lifting. The description adds no parameter-level meaning beyond that, which makes the baseline 3 appropriate.

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: 'Computes midpoint composite then renders as Western wheel' from 'two natal inputs'. This distinguishes it from single-chart siblings like astroway_render_wheel_western and from astroway_render_bi_wheel, though it never names any sibling explicitly.

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?

No statement of when to use this over alternatives such as the Davison or synastry variants, and no prerequisites or preconditions. The only routing signal is the '[Group: Visualization]' tag, which is implied rather than stated guidance.

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