Evaluate JavaScript

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

Adds substantial context beyond the annotations: output is capped, a thrown error returns as text, there is no user gesture, the call produces no observation, and browser_page must be called before the next browser_act. The single-CDP-connection constraint and the Chrome 144+ permission race are exactly the kind of operational hazard annotations cannot express.

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 purpose and return shape are front-loaded in the first sentence, and the operational warnings follow. Sentences are dense and long, but each carries distinct information; a slightly tighter phrasing of the second-driver warning would help.

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?

With no output schema, the description carries the return contract itself (string as-is, other values as JSON, capped) and explains state sequencing after the call. For a tool annotated destructive and open-world, the side-effect and session constraints are fully covered.

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 both expression and timeout_ms are already documented, and the description does not restate or extend timeout semantics. It adds related context (no user gesture, error-as-text) but nothing about parameter formats beyond the schema, so baseline 3 applies.

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 verb (evaluate) plus resource (one JavaScript expression in the page this session owns) and defines the return contract. It is clearly distinguishable from browser_act ('the indexed action space') and browser_page, so an agent can pick it without opening the schema.

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?

Gives concrete selection criteria: use for a programmatic read the indexed action space cannot express, or a one-off DOM operation. It also warns against starting a second CDP client. It stops short of explicit 'do not use this for X, use browser_act instead' routing, but the context is clear.

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