fx_eval

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

With no annotations, the description carries the transparency burden and does disclose that the input is a function body and that it may return a value. However, it omits material behavior for an arbitrary JS execution tool, such as error handling, async/promise behavior, return-value serialization, and side effects on page state.

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?

One short, front-loaded sentence conveys the operation, input format, and return behavior with no wasted words. The parenthetical efficiently packs the most important implementation detail.

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 that executes arbitrary JavaScript, the description is too thin: it does not explain how results are returned, whether promises are awaited, what happens on runtime errors, or what page context the script runs in. With no output schema and no annotations, these are significant gaps for an agent deciding whether and how to call the tool.

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 schema only says `js` is a string with no description, so the description provides the key meaning: the value is a function body, not a full script, and evaluation may produce a return value. This is genuinely additive, though it does not clarify optionality, async handling, or exact return conventions.

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 states a precise verb and resource: execute JS in the page. It adds a useful semantic cue — the script is a function body and may return a value — which clearly distinguishes this from the sibling interaction tools like fx_click and fx_navigate.

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 intended use is implied by the name and description, but there is no explicit guidance about when to prefer fx_eval over dedicated sibling tools, nor any warning against using it where a more specific fx_* tool would be safer. This is acceptable but relies on inference.

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