stream_screencast

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

No annotations are provided, so the description must fully disclose behavior. It does disclose that the tool is non-blocking, runs continuously at 60% JPEG quality, and returns the latest frame as base64 JPEG. However, it does not mention prerequisites (e.g., if a screencast session must be started first) or potential side effects like memory usage. With no annotations, the description is good but not fully explicit.

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 concise with no unnecessary text. It front-loads the key behavior in the first sentence, then bullets use cases. Every sentence adds value, and the structure is clean.

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 has zero parameters, no output schema, and no annotations, the description is relatively complete. It covers purpose, behavior, use cases, and return format. Missing is explicit mention of the need for an active screencast session, but the sibling tool 'browser_start_recording' suggests this context is available, so it's not a critical gap.

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?

There are no parameters (schema coverage 100%), so according to guidelines the baseline is 4. The description explains the output (base64 JPEG) but does not need to add param semantics since there are none.

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 clearly states it is a non-blocking visual capture that returns the latest frame from a screencast stream. It distinguishes itself from browser_screenshot by explicitly saying it does NOT block the browser's main thread or force a synchronous render, which helps an agent differentiate between the two tools.

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 provides explicit use cases (visual verification after action without blocking, Canvas/WebGL where AX tree is empty, monitoring animations/transitions) and directly contrasts with browser_screenshot, telling the agent when NOT to use this tool. This satisfies the highest level of guideline clarity.

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