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

Annotations already declare destructiveHint=false and readOnlyHint=false, so the description's job is lighter, yet it adds real behavioral substance: exactly what is reverted vs removed, and the reassurance that the rollback is itself recorded in history and can be undone. It does not mention permission/auth requirements beyond the schema's agent_key.

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 tight sentences, front-loaded with the core action and effect, then the optional filtering and the reversibility note. Every clause earns its place with no padding.

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, the description covers the essential effects (revert, remove, undoable) and the scoping options. It is nearly complete, missing only guidance on prerequisites or the sibling history tool.

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 schema already documents all five parameters; the baseline is 3. The description reinforces the semantics of since (a past moment) and the optional narrowing via key/writer, but adds little beyond what the schema strings already say.

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?

A specific verb-plus-resource definition ('Restore your charm's shared data to how it was at a past moment') that clearly distinguishes this from read_app_data, write_app_data, and app_data_history. The mechanism (revert changed keys, remove created keys) is spelled out so an agent knows exactly what operation this is.

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?

Clear context for when to call this: when you want to undo data changes back to an ISO timestamp, with optional narrowing by key or writer. It does not, however, name the alternative (app_data_history) or state when-not to use it, leaving that to inference.

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