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

With no annotations provided, the description carries the full behavioral burden. It discloses that the tool reads the composited surface, explains why this is reliable (independent of pooling/aliasing), warns against reading pooled targets, and notes the dependency on an already-open page. This gives the agent a clear mental model of the operation's behavior and its edge cases.

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?

Every sentence earns its place: purpose, technical nuance, prerequisite, and usage guidance are packed into four sentences with no filler. The key differentiator (composited vs. pooled) is front-loaded, and the alternative tool names are given inline, making it highly scannable and efficient.

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 tool of moderate complexity (WebGPU rendering inspection) with no output schema, the description covers everything an agent needs: what it returns (PNG image), why it is the reliable method, when to use it, what it does not do, and the required precondition. There is no critical missing information for correct 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?

The input schema already provides descriptions for all three parameters (pageId, fullPage, selector), giving 100% coverage. The description adds no additional parameter-level detail, so it meets the baseline of 3 but does not exceed it; the agent must rely solely on the schema for parameter meaning.

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-resource pair ('Capture a PNG screenshot of an instrumented page') and clarifies the output ('return it as an image'). It further distinguishes the tool from siblings by explaining it reads the composited page rather than intermediate buffers, naming read_texture and capture_frames explicitly, so an agent can separate it from similar functions without ambiguity.

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 states the exact when-to-use ('visually verify a rendering change') and when-not-to-use ('not to inspect intermediate G-buffer contents'), points to alternatives ('use read_texture / capture_frames'), and includes a hard prerequisite ('Requires a page opened via launch_browser/open_page'). This leaves no inference for the agent on how to select the tool.

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