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

Annotations already declare non-read-only, non-destructive, non-open-world, so the description's job is to add behavior context, and it does: it discloses a hard refusal guard tied to edit ownership and tells the agent what to do instead. It does not say what happens when there is nothing left to undo or what the call returns on success, which keeps it below a 5.

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 short sentences with zero waste; the core action is front-loaded and the guard plus fallback follow immediately. Every clause carries information an agent needs before calling.

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 one-optional-param tool with no output schema and full annotation coverage, the description covers purpose, failure guard, and recovery. The only real gap is the no-op case (no edit to undo) and the success return, which are minor given the tool's simplicity.

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% and the single optional projectId already documents its default ('the open one'), so the schema does the heavy lifting. The description adds no meaning about the parameter, leaving this at the baseline for high coverage.

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 ('Undo') and a precisely scoped resource ('your last edit'), which is more informative than the bare name because it clarifies that only the agent's own edit is reverted, not the user's. An agent can distinguish this from redo without opening any 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?

Gives an explicit when-not condition ('Refused when the last edit is the user's') plus a concrete remediation path ('fix yours with a new edit then'), which is real routing guidance rather than filler. It stops short of naming the redo sibling or stating whether undo is single-level or a stack, so it is clear but not exhaustive.

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