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

The annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely useful operational context not in annotations: the HTTP endpoint and a credit cost (100 credits, Tier 4). It does not add anything about latency, rate limits, or failure modes, so it falls short of 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?

The purpose sentence is front-loaded and dense with specifics, and the bracketed metadata lines are short and scannable rather than prose filler. Slightly more framing than strictly necessary, but nothing wastes the agent's attention.

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 input schema, an output schema (so return values need no explanation), and full annotations, the description only needs to establish purpose, cost, and endpoint — which it does. The main remaining gap is routing guidance relative to sibling HD tools, which is what keeps it from a 5.

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%, including very rich nested descriptions for chart1/chart2 (date/time formats, lat/lon, timezone handling, houseSystem letters) plus fields and precision. The description only restates the two required params, adding no meaning beyond the schema, so the baseline 3 is 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 (calculate), a specific artifact (Human Design connection chart), and the exact scope (between two people), then enumerates the four channel types returned. This distinguishes it clearly from sibling overlay/group tools such as astroway_hd_group_overlay and astroway_hd_penta, which are not pairwise.

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 or when-not-to-use guidance and no named alternative. The description tells the agent what the tool computes but leaves it to infer that this is the pairwise-compatibility tool rather than, say, a group overlay, and says nothing about prerequisites beyond the required-params note.

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