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

Beyond the annotations, the description discloses a lot: an explicit permission requirement, a two-phase confirmation protocol, and the crucial fact that the first call is a no-op that only validates arguments and returns a summary plus token. It also explains the validation behavior for unknown fields, which is far more than the false destructiveHint/idempotentHint hints convey on their own.

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?

Three sentences, front-loaded with purpose, then the permission, then the two-call protocol in chronological order. The short 'Two calls.' fragment is efficient, and the parenthetical about unknown fields earns its space by warning about `additionalProperties: false`.

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 mutation tool with no output schema and no annotations that cover safety, the description supplies the confirmation workflow and the shape of the first response (summary and confirm_token). It stops short of saying what the second call returns on success, which is the only material 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 only 50 percent (the `id` parameter has no schema description), so the description has to carry weight. It does explain the confirm_token lifecycle (omit on the first call, pass the returned token on the second) and that the second call reuses the same arguments, which meaningfully exceeds the schema text without fully defining `id`.

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?

The description names a specific verb and resource: "Undo removing a busy block", which tells the agent exactly what happens (restore a previously deleted busy block). It is clear but does not explicitly distinguish itself from siblings such as create_busy_block or update_busy_block; the agent must infer the distinction from the name alone.

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 spelled out precisely: the tool needs `calendar:write`, requires exactly two calls, and the second call happens only after the person approves the summary. What is missing is guidance on when to reach for this instead of create_busy_block or update_busy_block, which would fully separate it from its siblings.

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