Fill one or more form controls in order using snapshot references, ARIA refs, or CSS selectors. Automates web form input to enable structured data entry for browser automation tasks.
Fill one or more form controls in order.
| Name | Required | Description | Default |
|---|---|---|---|
| fields | Yes | ||
| pageId | No | Stable page ID; defaults to the session active page | |
| sessionId | No | Optional session ID; defaults to this MCP client active session |
Changes observed during successful MCP inspections.
v2026.8.14Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of disclosing behavior. It only reveals that filling happens 'in order,' but does not state whether it replaces existing values, waits for visibility, or handles missing elements. This is insufficient for a mutation-oriented tool.
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. Every word contributes meaning: 'one or more' establishes cardinality, 'form controls' specifies the resource, and 'in order' conveys behavior.
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?
Given the lack of annotations, output schema, and the presence of many similar sibling tools, this description is incomplete. It does not explain what happens after filling, how the tool behaves relative to other form-related tools, or any prerequisites. The description alone would not allow an agent to confidently invoke this tool without additional assumptions.
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 already documents target, pageId, and sessionId (67% coverage), so the description does not need to explain those. However, the description adds that the order of the fields array matters ('in order'), which is beyond the schema. It does not elaborate on the 'value' parameter, but its meaning is obvious from context.
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 uses a specific verb ('Fill') and resource ('form controls'), and adds scope ('one or more') and sequencing ('in order'). This clearly distinguishes it from generic tools like nex_browser_type or nex_browser_click, though it could more explicitly contrast with fill_credentials or fill_account.
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 provided on when to use this tool versus alternatives. There is no mention of use cases, prerequisites, or exclusions. Given the sibling list includes several related form-action tools (type, fill_credentials, select_option, check), this is a significant gap.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.