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

Annotations already declare readOnlyHint, idempotentHint, and closed-world, so safety is covered. The description adds two genuinely extra facts: conversion is DST-aware (a real behavioral risk area) and each call costs $0.001 via x402, a billing/payment behavior nothing in the annotations conveys.

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 compact sentences with the core purpose front-loaded and no filler. The price note is short and useful, though it sits in the same breath as the functional description rather than being clearly separated.

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?

Output schema exists, so return values need not be explained, and the tool is small (3 params, 1 required). Purpose, DST behavior, timezone naming, and cost are covered; only edge behaviors like omitting from_timezone with a wall-clock string are left to the schema.

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?

At 33% schema coverage, the description must compensate, and 'IANA time zones' clarifies the format expected by both to_timezone and from_timezone, which the schema documents only by example. It also echoes the instant/local-wall-clock distinction from the datetime parameter, though it does not mention that from_timezone is optional or the 'now' default.

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 ('Convert ... between IANA time zones') plus qualifiers that define scope: instant vs. local wall-clock input and DST-awareness. This is enough to distinguish it from siblings like city_time or date_add without opening a 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?

Usage is only implied by the stated scope; there is no explicit when-to-use, when-not-to-use, or named alternative among the many sibling date/time tools. The cost note gives an implicit call only when conversion is actually needed, but no routing guidance.

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