session_screenshot

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

The description discloses that it captures the CURRENT DOM state including mutations, which is a key behavioral trait beyond what annotations provide. It also mentions the built-in renderer and the return shape. Annotations only provide a title, so the description carries the burden and does so well, though it doesn't mention potential side effects or performance implications.

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 sentences with no waste. The key behavioral trait (current DOM state) is front-loaded, followed by the default behavior and return format. Every sentence earns its place.

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 screenshot tool with 6 parameters and no output schema, the description covers the essential context: what is captured, defaults, and return shape. It doesn't explain the selector/full_page/selector_all options in detail, but the schema covers those. The description is complete enough for an agent to call it correctly.

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 100%, so the schema already documents all parameters. The description adds context about defaults (viewport) and the return format, but doesn't add significant meaning beyond the schema. Baseline 3 is appropriate since the schema does the heavy lifting.

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 states a specific verb ('Screenshot'), a precise resource ('the session's CURRENT DOM state'), and clarifies that mutations from clicks/evals are included. It also distinguishes itself from generic screenshot tools by mentioning the built-in renderer and the return format. This is clearly differentiated from siblings like session_viewport and render_pdf.

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 notes that width/height default to the session's viewport and suggests pairing with session_viewport to show responsive layout. It doesn't explicitly state when NOT to use it versus alternatives like render_pdf or render_video, but the context is clear enough for an agent to infer appropriate usage.

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