Fill field in browser
browser_fillReplaces the entire value of an input, textarea, or contenteditable field by snapshot index in an agent Chrome tab, sending trusted text events and verifying the result without focusing the tab.
Instructions
Replace the whole value of a text field in one of the agent's tabs: focuses the element by its browser_snapshot index, selects everything in it and puts the text in through Chrome's own text input, so the page sees the same trusted input events as typing. Works on input, textarea and contenteditable fields, including inside web components (open shadow roots), in a background tab without selecting it or raising its window. Pass an empty string to clear the field. The reply says whether the field now holds exactly the text, and what it holds when the page changed or limited it (not for password fields). Use browser_type to add at the caret instead, and browser_request_credentials for passwords and codes. Never use the desktop press_key or type_text for a Chrome tab: those go to whichever Chrome window is in front, which can be the user's.
Tool call template
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"tab_id": "<tab_id>",
"index": "<index>",
"text": "<text>"
},
"name": "browser_fill"
}
}Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| text | Yes | The field's new value, replacing everything in it. Empty clears the field. | |
| index | Yes | Element index of the field from the latest browser_snapshot of this tab. An index naming a wrapper that holds exactly one field fills that field. | |
| tab_id | Yes | tab_id of one of the agent's tabs, from browser_open_tab or browser_list_tabs | |
| session_id | No | Stable task or thread ID. Pass the same value on every browser call for this task. Different IDs isolate tabs and cleanup within one MCP process. Omit for the default process session. | |
| return_state | No | Append a current snapshot and readiness status after acting. Without wait_for_selector, only a short pause and bounded navigation wait are used; SPA readiness is not guaranteed. Snapshot indices replace earlier ones. A timeout does not mean the action failed: re-observe with browser_snapshot before repeating it. | |
| wait_timeout_ms | No | Bound for wait_for_selector in milliseconds (default 8000, maximum 10000; 0 checks once). Requires wait_for_selector. Timeout preserves action success and returns current state. Use browser_snapshot with the same wait to re-observe without repeating an action. | |
| wait_for_selector | No | Wait for any visible element matching this CSS selector in the page, including open shadow roots (web components); child frames are not searched, and a timeout says how many were visible. On actions requires return_state=true. Returns readiness met, timeout or error; only this condition is checked, not general app readiness. Prefer a selector specific to the expected new UI. |