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

Annotations only state readOnlyHint=false (a write op). The description adds meaningful behavior: the markup dialect constraint, the JSX-with-fixed-values rule, the prerequisite to read mockup-guide first, and the refusal semantics ('lists every problem with its line — fix them all and retry once'). This is substantial context beyond the annotation.

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 tight sentences, front-loaded with what a mockup is, then the dialect prerequisite, then the attach option and refusal behavior. Every sentence carries information; no filler.

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 create tool with no output schema and full schema coverage, the description covers the artifact, the dialect, a prerequisite (mockup-guide), an optional attach behavior, and error handling on refusal. It does not explain the return payload, but no output schema exists so some gap remains regarding success response shape.

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 each parameter is already documented. The description adds the cross-parameter behavior of passing 'document' to attach in the same call, which is useful semantic value, but does not add format details beyond the schema. 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+resource ('Create a lofi wireframe mockup'), clarifies the artifact ('a static sketch of a screen or short flow'), and explains its role ('attached to a spec so readers see what the words mean'), clearly distinguishing it from edit-mockup and get-mockup.

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 concrete context: says to fetch mockup-guide before composing, and to pass 'document' to attach in the same call. Does not explicitly name an alternative for editing vs creating, but the create intent is unambiguous against siblings like edit-mockup.

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