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 does add non-annotation context — cost tier (10 credits) and the POST endpoint — but says nothing about what is calculated, whether a birth chart is required, or how lifespanYears affects the period count. With annotations carrying the safety burden, this is adequate-but-thin.

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?

Extremely short and front-loaded: one line of purpose followed by three bracketed metadata lines, with no wasted prose. Its brevity is close to under-specification rather than verbosity, but structurally it is clean.

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, so return values need not be described, and the input schema is well documented. Still, this is one of hundreds of chart-calculation siblings, and the description supplies none of the interpretive context (what a decennial period means, how many are returned, relation to lifespanYears) that would let an agent choose it confidently over the neighboring time-lord tools.

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% and the nested birth-data schema is extensively documented (formats, timezone handling, houseSystem letters), so the schema does the heavy lifting. The description adds no parameter meaning of its own — notably it never explains lifespanYears or the compact-mode fields/precision parameters.

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?

Names the technique ('Hand's decennial timing technique') and situates it in the Hellenistic Hand tradition, so an agent knows roughly what domain it computes in. However, it is nearly a restatement of the tool name ('decennials' → 'decennial timing technique') and never says what the tool produces or how it differs from siblings such as astroway_hellenistic_hand_perfections or astroway_hellenistic_brennan_time_lord_stack. No verb, scope, or output is stated.

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 guidance, no conditions selecting this over the many other Hellenistic timing siblings, and no prerequisites mentioned. The endpoint and credit cost lines are logistical metadata, not usage guidance.

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