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

Annotations already declare destructiveHint=true and idempotentHint=false, so the bar is lower, yet the description still adds real value: it scopes the destruction ('replaces only the targeted translation images'), states that unfilled frames retain their images, that excess sources are reported, and that assignment follows document order. Only auth/permission or failure-mode behavior is left unstated.

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 dense sentences, front-loaded with the core action, then sources, then ordering/retention semantics, then preview vs apply. No filler and no restatement of the title.

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?

Output schema exists, so return values need not be explained, and the preview mode's return behavior is noted anyway. For a 9-parameter nested-object tool the only real gap is how the three source parameters interact when more than one is provided, plus what platform/deviceType change.

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 only 33%, so the description carries weight here, and it does explain the three source-input parameters (localeFolders, screenshotPathsByLanguage, screenshotPaths) by describing them as alternative source modes. It does not state precedence or mutual exclusivity when several are supplied, and platform/deviceType go unmentioned.

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 precise verb and resource: assigning language-specific screenshot assets to existing translated device frames. The three source modes (locale folders, per-language paths, shared path list) further pin down what the tool consumes, which distinguishes it from siblings like upload_screenshots, apply_screenshot_style, or preview_screenshots.

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?

Clearly splits the two operating modes — preview returns assignments without saving, apply replaces only targeted translation images — which tells the agent when to use each. It stops short of routing to sibling tools (e.g., when to use preview_screenshots or upload_screenshots instead) or naming prerequisites such as frames already being translated.

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