Creating a Custom Environment#

Creating a custom MiniWoB++ environment is as simple as creating a new task HTML page, and then specifying the URL to the HTML file when registering the environment.

The following tutorial illustrates how to create a custom environment with the standard observation space and action space. For more advanced needs (customizing the spaces, creating a package, etc.), see this Gymnasium tutorial.

Creating the Task HTML Page#


To properly interface with the MiniWoB++ library, the HTML file must include core.css and core.js. These files are also available from the Python package (under html/core/).

Here is an example HTML file (custom.html):

<!DOCTYPE html>
<title>Custom Task</title>
<!-- The following CSS and JS are required. -->
<link rel="stylesheet" type="text/css" href="core.css">
<script src="core.js"></script>
// genProblem() will be called at the start of each episode.
var genProblem = function() {
  // core.randi(a, b) (from core.js) samples an integer between a and b (inclusive).
  let targetAmount = core.randi(2, 5), clickedAmount = 0;

  // Set the task utterance. This will become the "utterance" in the observation.
  document.getElementById("query").textContent =
      `Click Hello ${targetAmount} times, then click Submit.`;

  // Create the task UI.
  let hello = document.createElement("button");
  let submit = document.createElement("button");
  let amount = document.createElement("span");
  document.getElementById("area").replaceChildren(hello, submit, amount);

  hello.textContent = "Hello";
  hello.addEventListener("click", () => {
    amount.textContent = clickedAmount;

  submit.textContent = "Submit";
  submit.addEventListener("click", () => {
    if (clickedAmount === targetAmount) {
      // core.endEpisode(reward, timeProportional) ends the episode and sets
      // the reward (which can be read by Selenium). If timeProportional is
      // true, then the reward is scaled by the amount of time left.
      core.endEpisode(1.0, true);
    } else {
      core.endEpisode(-1.0, false);

window.onload = function() {
  // core.startEpisode() prepares the web page for an episode by showing the "START"
  // screen (it does not actually start the episode until "START" is clicked).
  // core.startEpisode() will also be automatically called at the end of each episode.
<!-- The following 3 divs are required. -->
<div id="wrap">
  <div id="query"></div>
  <div id="area"></div>

Registering the Environment#

The generic environment class MiniWoBEnvironment from miniwob.environment can be used as the entry point for the environment. The following keyword arguments should be specified:

  • subdomain: This should match the HTML filename.

  • base_url: This should point to where the HTML is; the URL {base_url}/{subdomain}.html should point to the task page.

  • field_extractor: This should be a function that takes the utterance string (that appears in the yellow box) and returns a list of fields as key-value tuples. One option is to not produce any field by specifying lambda x: [].

Here is example code (

import pathlib
from gymnasium.envs.registration import register
from miniwob.fields import create_regex_field_extractor

    'subdomain': 'custom',
    # Assuming that this file is in the same directory as `custom.html`:
    'base_url': 'file://{}/'.format(pathlib.Path(__file__).parent),
    # This helper method will produce a function that takes a string and returns
    # [('amount', ___)], where ___ is from the capturing group in the regex.
    'field_extractor': create_regex_field_extractor(
      r'Click Hello (\d+) times, then click Submit\.', ['amount'],

Using the Environment#

The following code is adapted from the example in the Basic Usage page:

import time
import gymnasium
from miniwob.action import ActionTypes
from miniwob.fields import field_lookup

# Import `` above to register the task.
import custom_registry

# Create an environment.
env = gymnasium.make('miniwob/custom-v0', render_mode='human')

# Wrap the code in try-finally to ensure proper cleanup.
  # Start a new episode.
  observation, info = env.reset()

  # Find the relevant HTML elements.
  for hello_button in observation["dom_elements"]:
    if hello_button["text"] == "Hello":
  for submit_button in observation["dom_elements"]:
    if submit_button["text"] == "Submit":

  amount = int(field_lookup(observation['fields'], 'amount'))
  for _ in range(amount):
    # Click Hello.
    action = env.unwrapped.create_action(ActionTypes.CLICK_ELEMENT, ref=hello_button["ref"])
    observation, reward, terminated, truncated, info = env.step(action)

  # Click Submit.
  action = env.unwrapped.create_action(ActionTypes.CLICK_ELEMENT, ref=submit_button["ref"])
  observation, reward, terminated, truncated, info = env.step(action)
  # Check if the action was correct. 
  assert reward >= 0
  assert terminated is True