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

With readOnlyHint/destructiveHint already covering the safety profile, the description goes well beyond them by disclosing the full return shape and, critically, the semantics of branch overlays ('a write under branch_id or an import on a branch appears there, not as a base change'). That distinction would otherwise cause an agent to misread the diff.

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?

It is front-loaded with the purpose and then the return contract, with no filler sentences. The inline shape dump is dense and verbose, but since no output schema exists it earns its place by carrying the return contract.

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 3-parameter, nested-object read tool with no output schema, the description adequately covers inputs and return structure, especially the branch-vs-base distinction. It omits any mention of the `model_id` scoping requirement for user-scoped keys, a minor gap given the schema documents it.

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 description coverage is 100%, so the schema already documents the `from`/`to`/`model_id` shapes and their UUID/revision semantics. The description largely restates these ('exactly one of revision_id / version_number / id', 'omitted = live model') rather than adding new syntax or format detail, so the baseline of 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?

The opening sentence names a specific verb and resource ('Returns the semantic diff between two revisions of a model'), so the operation is unambiguous. It never names or contrasts itself with a sibling such as layerz_history, so it stops short of full differentiation.

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?

It clarifies the default behavior ('without `to`, the diff runs against the live model'), which is useful selection context. However, it never says when to pick this tool over layerz_history or other read tools, and offers no exclusions or prerequisites.

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