select_optionSelect one or more options in a page's element by visible label or value.
Selects one or more options of a element by visible label or value.
| Name | Required | Description | Default |
|---|---|---|---|
| ref | Yes | Element ref from page_snapshot or find, e.g. "e12". | |
| tabId | No | Tab to act on. Defaults to the session target tab (see tab_select). | |
| values | Yes | Options to select. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false and openWorldHint=true, so the agent knows this mutates page state. The description adds only that multiple options may be selected; it does not say whether existing selections are replaced or appended, whether change events fire, or what happens when a label matches nothing.
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?
A single sentence with zero filler, front-loaded with the verb and resource. It is appropriately sized for a simple tool, though it leaves room that could have carried a clause about selection semantics.
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?
No output schema exists, and all parameters are schema-documented, so the basics are covered. For a state-mutating browser tool, however, the definition omits failure behavior for unmatched labels/values and the effect on pre-existing selections — details an agent needs to call it correctly.
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 coverage is 100%, so all three parameters are already documented, including the ref format and tabId default. The description's 'by visible label or value' does add useful meaning to the values array beyond the schema's brief 'Option label or value', but only marginally.
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 and resource ('Selects one or more options of a <select> element') with a clear scoping mechanism (visible label or value). It is distinguishable from click/fill_form by the <select> element reference, though it never names a sibling explicitly.
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?
Usage is implied by the '<select> element' constraint, which lets an agent infer it should be preferred over generic fill_form or click for dropdowns, but no when/when-not rules or alternatives are stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.