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

Annotations already declare this a safe, idempotent, non-destructive read, so the safety profile needs no restating. The description adds a credit price (10 credits, Tier 1) and the mod-90 projection math, which are genuine extras, but it says nothing about whether the default output is JSON or SVG despite the title advertising SVG.

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?

One dense, front-loaded sentence carries the domain definition, followed by three short bracketed metadata lines. Zero filler, though the endpoint string duplicates what the transport layer already knows.

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?

An output schema exists and the deep birth-data schema is fully annotated, so little is owed on params or returns. The gaps are the missing format default (the title implies SVG while the schema defaults to json) and the absence of any routing versus the ten other render_* siblings.

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% (birth data, timezone/timezoneOffset behavior, houseSystem letters, options.theme, fields/precision all documented in the schema), so the baseline is 3. The description contributes no parameter meaning of its own.

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 action ("Plots planets at (longitude mod 90)° across 4 quadrants") on a named resource (Cosmobiology 90° dial / Hamburg School cosmogram), which is clearly distinct from wheel_western or bi_wheel. However it never names a sibling or says what makes this the right chart versus the other render_* tools, so differentiation is by domain knowledge only.

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?

There is no when-to-use, when-not-to-use, or alternative routing anywhere in the text. The bracketed group/endpoint/cost lines are metadata, not guidance, so an agent has to infer from the tool name alone when a 90° dial is the intended output.

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