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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful operational context the annotations cannot: the cost (50 credits, Tier 3) and the underlying endpoint. It still says nothing about latency, size of the returned activation set, or whether the transit moment defaults to now.

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 front-loaded sentences carry the whole functional story, with the optional overlay stated second. The bracketed metadata lines are compact and each adds information (group, endpoint, cost) rather than restating the name, so 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 a rich nested input schema at 100% coverage, an output schema for return values, and annotations covering the safety profile, the description only needed to state purpose, optional overlay, and cost — which it does. It is marginally thin on when the tool should be preferred over the adjacent HD tools, but nothing required to call it correctly is missing.

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%, so the schema already documents date/time/lat/lon, timezone handling, ayanamsa, houseSystem and the natal overlay fields. The description only echoes the overlay capability and adds no syntax, format, or defaulting detail beyond what the schema provides. Baseline 3 applies.

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 ('Calculate ... Human Design transit activations') and adds scope ('optionally overlay on natal chart to show combined defined centers and channels'), which separates the overlay mode from a plain transit read. It does not name any sibling such as astroway_hd_design_date or astroway_hd_group_overlay, so an agent must infer the boundary itself. The word 'current' is also slightly at odds with a tool whose body requires an explicit date and time.

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?

'Optionally overlay on natal chart' implies the two modes of use, so the agent can infer when to supply natalDate/natalTime. However, there is no explicit when-to-use guidance, no exclusion (e.g. group vs single-chart overlays), and no pointer to the sibling tools that cover adjacent Human Design operations.

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