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

Adds substantial context beyond annotations: remove is two-phase ('first call asks, then requires confirm:true' deletes nothing), only Capable-created blocks can be modified, create is capped at 24h, list caps at 62 days, and request_id reuse is limited to retrying the same block (consistent with idempotentHint=true). It does not describe the confirmation-prompt return shape or failure modes when editing a non-Capable block, so it falls short of the top score.

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 scope, then a compact per-action block of constraints, then 'When to use' and an example. Nearly every clause carries operational information, though the action paragraph is a dense run-on that could be split for faster scanning.

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 13-parameter, four-action tool with an output schema and annotations already present, the description covers the prerequisites (Capable-created blocks, confirm flow, request_id freshness, duration/range limits) an agent needs to call it correctly. Remaining gaps — per-action return contents and the confirmation-prompt payload — are partly covered by the output 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?

Schema coverage is 100%, so the baseline is 3, but the description adds cross-field semantics the schema lacks: create requires title/starts_at/ends_at with a max 24h span, request_id must be fresh and reused only for retries, update with starts_at alone preserves duration, and show_as defaults to busy gating booking pages and find_times. Minor params (time_zone, notes) are left to the schema.

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 concrete verb set (manage/create/update/list/remove) over a specific resource — personal Google/Outlook calendar blocks with no attendees — and immediately bounds the scope: 'nothing is sent.' It also names the sibling it is not (find_times for meetings with others), so the agent can distinguish it without opening either 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?

The 'When to use' line gives positive triggers (block focus time, add reminders, adjust your own blocks) and an explicit alternative plus its condition ('use find_times for meetings with others'). A worked example ('Block 9–11 tomorrow for writing') further anchors invocation.

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