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

Annotations already declare readOnly, idempotent, and non-open-world, but the description adds substantial behavior beyond them: a hard cap of 200 occurrences, dual local/UTC output, a gap:true flag on DST-shifted occurrences, rejection of rules requiring over 50,000 candidate evaluations, and the $0.05 x402/USDC-on-Base pricing. This is exactly the extra context an agent needs before invoking a paid, quota-limited tool.

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 is front-loaded in the first sentence, followed by inputs, capabilities, edge-case behavior, and pricing in compact order. It is dense but nearly every sentence carries information; the pricing clause is a slight tail-end addendum but still actionable.

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 no output schema, the description correctly describes the return shape (local wall-clock plus UTC instants, gap flag, 200-item cap), the cost, and the computational rejection limit. Remaining gaps are minor: error behavior on malformed RRULE strings and pagination semantics for the after parameter are not described.

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%, so the baseline is 3, but the description adds genuine value the schema lacks: it enumerates which RRULE parts are supported (FREQ, INTERVAL, COUNT, UNTIL, BYDAY, BYMONTHDAY, BYMONTH, BYSETPOS, WKST), which is the key uncertainty for a rule-expansion call. It does not clarify the after/skip semantics beyond the schema, so it falls short of a 5.

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?

The description opens with a specific verb and resource: expanding an RFC 5545 recurrence rule into concrete occurrence timestamps, and immediately enumerates the accepted inputs (RRULE, DTSTART, zone, EXDATE, RDATE). This clearly separates it from sibling tools like timezone_convert, calendar_convert, and dst_transitions, which handle one-off conversions rather than recurrence expansion.

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?

Usage is implied rather than stated: an agent can infer this is the tool for turning a recurrence rule into a list of dates, and the DST-gap and 50,000-evaluation notes hint at edge cases. However, it never says when to prefer this over calendar_convert or dst_transitions, nor any explicit preconditions or exclusions, leaving routing to inference.

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