screenshot

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

With no annotations, description bears full burden. Discloses return format (image object with MCP rendering), includes details on Chromium scaling and optional dependencies, and describes failure modes. Could add more depth on image encoding but sufficient.

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?

Highly concise: three sentences cover core purpose, usage, return value, and failure condition. No wasted words, front-loaded with key action.

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 5-parameter tool with no output schema, description explains return shape and rendering, mentions environment variables, and covers failure cases. Could clarify image format (e.g., PNG base64) but is generally complete.

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 description adds value beyond schema by explaining default scale behavior (env var fallback), Chromium-specific downscaler algorithm, and the purpose of includeImageInContext. This extra context aids correct parameter usage.

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?

Description clearly states 'Capture a screenshot of the device screen' and lists supported device types (iOS simulator, Android emulator, Apple TV simulator, Vega, Chromium app). It is unambiguous and distinguishes from sibling tools, none of which duplicate this function.

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?

Provides clear when-to-use guidance: 'when you need a baseline image before an interaction or to inspect the current screen state after a delay.' Also mentions failure condition when backend unreachable. Lacks explicit when-not-to-use, but the tool is straightforward.

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