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

Annotations only give generic safety hints (readOnlyHint=false, destructiveHint=false, idempotentHint=false); the description adds the real behavioral facts: required auth scope, a two-phase confirm flow, that the first call mutates nothing but validates arguments and refuses unknown fields by name, and that it returns a summary plus a confirm_token. That is substantial context an agent could not infer from the annotations.

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?

Four short sentences, front-loaded with the action and auth requirement, then the two-call protocol in execution order. No filler or repetition.

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 explains what the first call returns (summary and confirm_token), and covers auth and validation behavior. It leaves the second call's response shape unstated and says nothing about the timezone parameter, which is the only meaningful gap.

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 50%. The description clarifies confirm_token usage, but the schema's own description already covers that, so little is added. The required `timezone` parameter is undocumented in both schema and description, so the description does not compensate for the coverage gap. Baseline 3 applies.

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 ("Add a busy block"), which is clearly distinguishable from sibling mutation tools like update_busy_block, delete_busy_block, and skip_busy_occurrence. It does not explicitly name those alternatives, so it stops short of a 5.

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?

Gives a concrete precondition (`calendar:write`) and a precise usage sequence: call once as a dry run, show the summary to the person, then call again with the same arguments plus confirm_token only after agreement. It does not say when to prefer this over creating a block via another path (e.g., set_import_busy or calendar sync), so no explicit exclusions.

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