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

Annotations already declare the safe-read profile (readOnly, idempotent, non-destructive, openWorld), and the description adds substantive extra context: pricing ($0.002/call via x402 on Base), an auth mechanism (prepaid x-credit-token header), a free tier (1 call/day), and no API key requirement. These are behavioral details the annotations cannot convey.

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?

Front-loaded with the core purpose, then defaults, limitations, and payment terms. It is dense but every clause is operational (format, defaults, limits, billing). The pricing/payment sentence is longer than ideal but is genuinely needed for correct invocation of an x402 tool.

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 explained. The description covers inputs, format, defaults, limitations, and payment/auth, leaving nothing an agent needs to call it correctly unspecified.

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 baseline is 3, but the description adds real meaning: 'Pass zones= IANA list' specifies the format the schema only calls 'comma-separated', and it documents the default 09–17 local window that governs startHour/endHour. Required input (zones) is also reaffirmed.

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 with scope: 'Find 30-minute UTC slots where every zone is inside a local window (default 09–17) on a given date.' It even distinguishes itself from a plausible sibling by noting it 'Does not know holidays or personal calendars,' so an agent can tell it apart from holiday_calendar/business_days.

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?

Clear context is given: overlap office hours across timezones, pass an IANA zones list, defaults to 09–17. It discloses the limitation (no holidays, no personal calendars) which is effectively a when-not signal, but it does not explicitly route the agent to a named alternative for the holiday case.

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