vision_diff

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

With no annotations provided, the description carries the full burden. It does disclose that the tool compares images and can produce pixel-level diffs (via include_pixel_diff), but it does not mention whether the tool is read-only, handles remote/local sources differently, or any potential side effects. Some behavioral context is present, but significant gaps remain.

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?

The description is well-structured: a clear purpose sentence, explicit usage rules, then a compact arg list. Each line earns its place, and the layout makes it easy to scan. No redundancy or fluff.

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?

Given the tool's complexity (8 params, no schema descriptions, no annotations) and the existence of an output schema, the description covers purpose, usage, and parameter semantics. It omits details like error handling or return format, but the output schema likely covers that. Minor gaps in edge-case behavior prevent a perfect score.

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 0%, so the description must compensate, and it does thoroughly. It explains all 8 parameters, including the relationships between source, path, and data variants, and flags backward compatibility. This is far more useful than the bare schema.

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 description opens with a specific verb and resource: 'Compare two UI screenshots or a design mockup with an implementation screenshot to identify visual differences.' It clearly distinguishes this tool from siblings like vision_inspect, which is called out as the alternative for single-image analysis.

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?

The description explicitly states when to use: 'Use this tool ONLY when comparing an expected/reference UI with an actual implementation.' It also lists exclusions and alternatives: 'Do NOT use for: analyzing a single image (use vision_inspect), error diagnosis, general image comparison.' This is exemplary usage guidance.

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