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

Annotations already declare non-read-only, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely new context: export-allowance consumption (a quota cost the annotations do not express), a hard limit of ten screens per validated iOS package, and which parameter enforces idempotency. It does not say what happens when the limit or allowance is exceeded.

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?

Four sentences, front-loaded with the action and immediately followed by capabilities, limits, and cost. Dense but every clause carries information; the middle sentence packs three constraints together, which slightly hurts scannability.

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 six-parameter mutation with nested objects, the description covers the operational constraints an agent must know (quota, screen cap, idempotency) and an output schema exists to explain results. Missing only failure behavior and the preview-vs-render distinction.

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?

With 0% schema description coverage, the description carries the whole burden and does well: it explains resolutions ('preset or custom dimensions'), variantId ('active or specified variant'), formats ('phone-format layouts'), languages ('screenshot translations'), and the idempotencyKey reuse rule. Only projectId is left unexplained, and 'independent phone-format layouts' is a slightly cryptic gloss for formats.

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 and resource: 'Starts a render of saved screenshot translations' for an active or specified variant. It is distinguishable from list/prepare tools, but it never names its closest sibling (preview_screenshots) or explains the relationship, which is the main ambiguity an agent faces here.

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 implied by 'Uses export allowance' and 'Starts a render', which hints this is the committing/consuming step rather than a preview, but no explicit when-to-use or when-not-to-use guidance is given. Nothing tells the agent when to pick this over preview_screenshots or render_graphics.

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