Jev Ultrafast ⚡
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A browser agent with a dynamic, indexed action space.
Give it one goal. TypeSafe's Jev picks an operation and an element. A small LLM writes text only when the operation is TYPE_TEXT.
Zürich → London on Google Flights in 7.1 seconds. One natural-language goal, actual text generation, and loading waits included.
Watch the MP4 · Measurements · Read the loop
The action space
Every observation produces a new element table:
[1] button Change ticket type · Round trip
[2] combobox Where from? · San Francisco
[3] combobox Where to? · empty
[4] textbox Departure · empty
...
The operations are CLICK, TYPE_TEXT, SELECT, SCROLL_UP, SCROLL_DOWN, WAIT, DONE, and BLOCKED. Only supported operations and targets are offered.
one TypeSafe request
┌───────────────────────────┐
page → element table → operation │
│ click_target │
│ type_text_target │
│ select_target, if present │
└─────────────┬─────────────┘
use the matching target
│
CLICK [7] ─────┤──→ browser
TYPE_TEXT [3] ─────┘
↓
small LLM → text → browser
Target questions are speculative. If the operation is CLICK, only click_target can execute. Two decisions, one network round trip. Each target head contains only compatible elements. Native dropdown choices carry an observed element/option index.
There are no site-specific action scripts or prepared field strings in the policy. The Flights example supplies a goal and independently verifies the outcome. The screenshot renderer adds labels afterward; it does not drive the browser.
Try it
git clone https://github.com/browser-use/jev-ultrafast.git
cd jev-ultrafast
uv sync
cp .env.example .env
# Add TYPESAFE_API_KEY and TEXT_MODEL_API_KEY.
uv run jev
Open http://127.0.0.1:8766 and click Start demo → Run automatically. The inspector shows numbered elements, operation probabilities, target probabilities, and executed actions. Choose next pauses before execution.
Chrome connects through Browser Harness, installed by uv sync. Run uv run browser-harness --doctor if it needs connecting. Allow remote debugging in Chrome when prompted.
TEXT_MODEL_API_KEY is an OpenRouter key in the example configuration. The current demo uses inception/mercury-2.5 with reasoning disabled. Gemini, GLM, and DeepSeek can also use the OpenAI-compatible text helper; configure the appropriate model, endpoint, and reasoning setting.
Use the library
from jev_ultrafast import Agent
with Agent(
"https://www.google.com/travel/flights?hl=en",
"Find one-way flights from Zurich to London on September 20, 2026, "
"for one adult in economy. Stop when matching flight options are visible.",
) as agent:
for state in agent.run():
print(state["elapsed_ms"], state["status"])
Run with uv run --env-file .env python your_script.py. The same policy can run a different task:
uv run --env-file .env python examples/run.py \
--url https://en.wikipedia.org/wiki/Main_Page \
--goal 'Find and open the Wikipedia article about Gödel’s incompleteness theorems.'
uv run --env-file .env python examples/flights.py --keep-open performs the flight search, checks the actual route/date/results, and saves its trace. It does not select or book a flight.
Why it moves
- One request per decision cycle. Operation and target heads share the same observed state.
- No screenshots in the default agent loop. Jev consumes structured state. The inspector opts into screenshots; the video uses a separate continuous screencast.
- One browser call per snapshot. Read visible controls, their names, values, and text atomically. Keep references to the actual DOM nodes.
- Validate the selected target. Clicks check the document, form values, target, and nearby context. Animation alone does not force another prediction. Resolve current geometry and reject covered controls before input.
- Wait for useful state. After typing into a combobox, wait for visible suggestions, capped at 200 ms. Other interactions get at most two animation frames or 50 ms. These reads happen after execution is logged.
- Keep hidden tabs rendering. Focus emulation prevents background animation throttling without switching Chrome's visible tab.
- Send visible text. Offscreen article bodies and footers do not fill the model context.
- Reuse an interrupted text request. A generated value survives a stale-page retry only if the entire text-helper input is unchanged.
Every executed target is resolved from an observed node. The executor rechecks page freshness and click occlusion. Model output never becomes selectors, coordinates, shell commands, or executable JavaScript. Text-helper output must parse as a small JSON object before typing.
Small enough to read
| File |
Job |
| agent.py |
The complete loop and text-helper handoff |
| snapshot.js |
Atomic DOM snapshot, indexed controls, freshness guards |
| browser.py |
Browser connection, current geometry, execution |
| model.py |
Dynamic operation/target heads and text generation |
| questions.py |
Model instructions |
| demo.py |
Local inspector |
Evidence and limits
The current video is a 7,073 ms Google Flights run. Timing starts after initial page observation and includes model calls, generated text, browser work, stale decisions, and loading waits. A fresh independent check verifies the one-way setting, Zürich, London, September 20, 2026, and visible flight options. The video plays at 1×, with no opening hold and a 0.5-second final hold.
In six alternating runs with identical models and settings, both versions passed 3/3. Median task time went from 9.450 s → 7.092 s, a 25% reduction; median browser protocol calls went from 1,092 → 101. This is three repeats of one task on one browser profile, not a general reliability benchmark.
The same policy opened the requested Wikipedia article in 2.798 s and passed a local hotel search/filter task in 1.896 s. Runs, failures, source hashes, and measurement boundaries are in performance.md.
A DONE choice still requires independent outcome verification. The DOM reader handles common HTML and ARIA controls, not the full accessible-name specification. Shadow roots, frames, canvas, uploads, pop-up tabs, nested scrolling, and arbitrary keyboard widgets remain outside this MVP. Owned tabs share the existing Chrome profile.
Development
uv run ruff check .
uv run pytest
node --check jev_ultrafast/static/app.js
node --check jev_ultrafast/snapshot.js
uv build
Tests are offline. uv run python scripts/check_guards.py checks real controls in a local browser without model calls. Live examples and recording scripts make paid API calls. scripts/record_flights.py <new-folder> captures original browser timestamps; scripts/render_demo.py <recording-folder> renders that verified run at 1× and crops out the Google account strip. Credentials and raw traces stay ignored.
Browser Use · Browser Harness · TypeSafe speculative fan-out
一个拥有动态、可索引操作空间的浏览器智能体：你只需给它一个自然语言目标，它会自己挑选每一步操作和目标元素——例如，一次从苏黎世到伦敦的 Google Flights 搜索，大约 7 秒就完成了。