session_screenshot

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

Annotations only provide a title, so the description carries the behavioral burden. It adds valuable detail: the screenshot reflects the current DOM including mutations, is rendered by the built-in renderer, and returns a structured base64 payload. It does not explicitly state non-mutating behavior, but the action itself makes that clear.

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 filler: the first states the core action and DOM context, the second clarifies default sizing and pairing, and the third gives the return shape. Information is front-loaded and 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?

Given six parameters and no output schema, the description appropriately covers the non-obvious behavior (mutations included, built-in renderer, default sizing) and supplies the return object shape. Remaining parameter details are already in the schema; error conditions and format caveats are not addressed, but are not critical for invocation.

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 every parameter already has a clear description, including width/height defaults and selector behavior. The description reinforces the viewport default and adds the session_viewport pairing, but adds little semantic meaning beyond the 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?

States a specific operation: capture the session's current DOM state as a base64 PNG via the built-in renderer, explicitly including mutations from clicks/evals. This clearly differentiates it from siblings like session_viewport (viewport metadata) and session_state (state inspection).

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 context: use it to capture the live, mutated DOM, and pair it with session_viewport to evaluate responsive layout. It does not enumerate exclusions or alternative screenshot tools, but no sibling directly competes, so the guidance is sufficient.

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