Run JavaScript in the active browser page during an engagement and return the serializable result, enabling scripted inspection of live targets.
Evaluate JavaScript in the active page and return its serializable result.
| Name | Required | Description | Default |
|---|---|---|---|
| argument | No | ||
| expression | Yes | ||
| session_id | Yes | ||
| engagement_id | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden but only mentions that the result is serializable. It omits critical traits for arbitrary JavaScript execution, such as side effects on the page, network access, error behavior, and whether the operation is sandboxed or destructive.
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 a single, front-loaded sentence with no wasted words. It states the action, scope, and return constraint immediately.
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?
Although an output schema exists and covers return values, the description is insufficient for a tool that executes arbitrary JavaScript in a browser session. It lacks usage context, safety implications, parameter explanations, and session/engagement prerequisites.
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 0% across four parameters, and the description adds no meaning beyond the schema. It does not explain the purpose of argument, session_id, or engagement_id, nor does it clarify expression syntax or expected format.
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 names a specific verb ('Evaluate'), resource ('JavaScript'), and scope ('active page'), clearly setting it apart from sibling browser tools like snapshot, action, or navigate. An agent can understand the core operation 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?
No guidance is given on when to use this tool versus alternatives such as websex_browser_action, websex_execute, or websex_python. There are no prerequisites, exclusions, or contextual triggers to help an agent choose correctly.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.