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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: the ephemeris methodology (true lunar node, Design moment at 88° solar arc), historical time zone handling, the uncertainty-window behaviour, and the fact that each element carries a title plus one-line summary. These are non-obvious traits an agent could not infer from structured fields.

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?

Three dense sentences, front-loaded with the purpose before the output inventory and methodology. The long enumeration of chart elements is justified because there is no output schema, though it is at the edge of what an agent needs to decide whether to call the tool.

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 6-parameter, no-output-schema tool, the description supplies the missing return-value information (chart sections, activations, titles and summaries) and explains both the deterministic calculation basis and the uncertainty behaviour. Nothing needed to invoke it correctly is absent.

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 coverage is 100% and every parameter is documented there, so the description adds little per-parameter meaning beyond restating that time matters for uncertainty. Baseline 3 applies because the schema carries the parameter burden.

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?

Opens with a specific verb+resource ('Computes a person's Human Design chart from date, time and place of birth') and then enumerates exactly what the result contains (Type, Authority, Profile, centres, channels, 26 activations). This is clearly distinct from compare_charts and get_transits without needing to open either schema.

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 context of use is unambiguous: single-person chart from birth data, with an explicit note that unknown/approximate birth times trigger the uncertainty listing. It does not explicitly name alternatives such as compare_charts for two people, so it stops short of full when/when-not routing.

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