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

Annotations already declare readOnlyHint=true, and the description aligns with that by saying 'Read' and referencing GET. It adds useful behavioral context beyond annotations: the return shape '{ pages, free_busy }' and the account-wide calendar scope.

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 concise sentences with no filler. The core action is front-loaded, followed by the return shape and API method, making it easy for an agent to parse quickly.

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?

For a read-only tool with 5 fully described parameters and no output schema, the description gives the essential return envelope and scope. However, it does not clarify default window behavior when from/to are omitted, which could matter since only tzid is required.

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%, so the baseline is 3. The description's phrase 'over a time window' and 'across the account's calendars' conceptually maps to from/to and calendar_ids, but it does not add parameter-level detail beyond what the schema already provides.

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: 'Read free/busy information across the account's calendars over a time window.' This clearly distinguishes it from sibling tools like cronofy_read_events or cronofy_list_calendars because it targets availability data, not event details or calendar metadata.

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?

Provides clear context: this is for free/busy availability across account calendars within a time window. It does not explicitly name alternatives or state when not to use it, but the scope is sufficiently clear that an agent can infer the appropriate situation.

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