Moli is a production-ready headless browser for AI agents. Its on-demand layout
and rendering design combines a complete browser runtime with a lightweight
resource footprint.
Moli helps your AI agent fetch and extract web pages, search the web, and
automate browser tasks.
Use it through the CLI, CDP, WebDriver Classic, or WebDriver BiDi.
Moli supports Linux, macOS, and Windows.
Quick start
Give this prompt to your AI agent:
Install the skills under https://github.com/lexmount/moli/tree/main/skills,
follow their instructions to download and install the latest prebuilt Moli
binary, then use moli-webfetch to fetch https://example.com and show me the
result.
Direct installation
On Linux or macOS:
curl --proto '=https' --tlsv1.2 -fsSL \
https://github.com/lexmount/moli/releases/latest/download/moli-installer.sh | sh
To export a page after an explicit interaction, combine --eval (or
--eval-file) with --dump. The expression runs after page readiness;
promises are awaited, and any pending navigation is followed before export.
Its return value is discarded without serialization. An exception fails the
command without emitting a dump.
Only the supplied expression performs interactions. Without --dump,
--eval retains its expression-value output behavior.
Run fetch --help for the complete option list, including output formats,
page-load/response waits, profiles, proxy settings, resource policies, and
tracing options.
Start the automation server
# Basic automation server for DOM-first workloads
moli serve
# Enable real geometry, coordinate input, and screenshot/screencast surfaces
moli serve --layout
# Also fetch optional image, font, audio, video, media, and text-track resources
moli serve --layout --resource
The same endpoint serves all three protocols: CDP, WebDriver Classic, and
WebDriver BiDi. Playwright can connect directly over CDP:
The WebMCP playground includes a CLI to list
and call any site's native WebMCP tools, plus booking, restaurant, and pizza demos.
Why Moli
Three qualities matter most for agent workloads, and Moli brings them together:
Full-featured — real JavaScript, DOM, CSS, networking, storage, layout,
screenshots, and standard automation protocols, all integrated into one
headless browser.
Fast — most automation requests never need visual rendering, so
structure-first operations skip layout and paint entirely.
Resource-efficient — layout and pixels are generated only when needed,
so Moli does not have to continuously maintain and update a fully rendered
visual state.
What most browser automation tasks actually need is page structure, not a
continuously rendered visual world. Moli treats the native DOM and style state
as the single source of truth, triggering layout or software paint only for
operations that genuinely require them.
Agent request
What Moli does
Extract HTML/Markdown, query the DOM, run JS, inspect network/storage
Reads browser runtime state directly — does not trigger layout or paint
Read an element's box, hit-test coordinates, send coordinate input
Runs one layout calculation and retains only the latest frozen layout tree
Capture a screenshot
Rebuilds from the current DOM/style, replaces the frozen tree, renders a fresh frame, and discards its paint state after use
Poll a screencast
Compares generation metadata only; clean state emits no frame, while changed state rebuilds and emits one fresh frame
Moli still includes the complete set of capabilities: V8, CSS, layout, text
shaping, hit-testing, software paint, and more. The only difference is when
visual work runs and how long its results are retained. This cost model is
especially well suited to crawling, browser-use agents, retrieval pipelines,
evaluation environments, and reinforcement-learning workloads.
Current capabilities
Complete web runtime — streaming HTML parsing, native DOM, V8 JavaScript,
modules/timers/microtasks/events, iframes and workers, CSS cascade,
Fetch/XHR/WebSocket, cookies, WebCrypto, and profile-scoped storage
(localStorage, IndexedDB, OPFS).
Extraction-optimized outputs — the CLI directly produces HTML, Markdown,
JSON, semantic text trees, and frame-aware serialization, with
selector/script/response waits and network tracing.
Unified automation binary — CDP, WebDriver Classic, and WebDriver BiDi
share the same kernel and scheduler. No separate ChromeDriver, geckodriver,
or browser installation is required.
Real visual capabilities on demand — add --layout to enable complete box
construction, Taffy layout, Parley text layout, layout-backed
hit-testing/input, viewport
screenshots, and low-frequency CPU-rendered DevTools screencast frames.
Controllable operational options — profiles, cookies, HTTP cache, proxies,
resource families, connection limits, timeouts, private-network policy,
user-agent overrides, diagnostic logging, and network diagnostics are all
available.
Moli's relationship with Lexmount
Moli is Lexmount's open-source headless browser; Lexmount Browser is the managed
cloud runtime and control plane built around it.
The open-source headless browser is fully usable without Lexmount Browser.
Cost controls
Expensive browser operations in Moli require an explicit opt-in and are never
enabled by default:
Mode or option
Behavior
Default
LayoutPolicy::Mock — deterministic geometry in a compatible format, with no real layout or paint
--layout
LayoutPolicy::OnDemand — real layout, geometry, hit-testing, coordinate input, screenshots, screencast
Selectively enable the persistence required by the workload
Layout is an on-demand snapshot rather than continuously maintained state. The
first geometry request (a cold start) builds a working layout tree from the
current DOM/style, freezes its canonical geometry into an immutable,
DOM-independent FrozenLayoutTree, and retains only that latest tree. Ordinary
geometry reads may reuse it even if the page has changed. Screenshots always
rebuild and replace the frozen tree. Each screencast subscription remembers
only an opaque visual-state token: an unchanged token suppresses the poll,
while a changed token triggers one fresh frame. Paint results are never reused.
Architecture
Moli is a standalone browser kernel, not a Chromium wrapper. It is built in
Rust, has its own ownership and lifecycle rules, and relies on:
libcurl — network transport and multi-request runtime
html5ever — HTML parsing
rusty_v8 / V8 — JavaScript execution
Servo/Stylo — selectors, cascade, computed style
Taffy + Parley — box and text layout
AnyRender/Vello CPU, usvg, and the Rust image ecosystem — software rendering
Document and style have a single source of truth: the native DOM and its Stylo
integration. Every real refresh builds a temporary working tree from that
source, optionally produces and consumes one fresh paint snapshot, freezes the
canonical box/fragment geometry into a compact FrozenLayoutTree, and discards
the working tree, style borrows, layout caches, diagnostics, and paint state.
Screencast tokens contain generation metadata, never layout or paint data.
Source lookup and hit-test candidates are derived from the frozen tree when
queried. The system has no incrementally maintained layout tree, damage graph,
retained display list, GPU compositor, or persistent window.
Benchmark
The following measurements show Moli's current capability envelope. They cover
real websites, automation clients, Chromium/WPT behavior checks, and a large
nextest regression suite.
Mixed public-web crawl test
The test covers 192 public URLs from major Chinese and international sites. A
page only counts as successful if it produces meaningful content after
JavaScript runs — an HTTP 200, challenge page, login wall, empty response, or
shell-only application does not count.
Browser
Useful pages
Success rate
Median time
Median RSS
Moli
103
53.6%
1.43 s
73 MiB
Chrome Headless
101
52.6%
1.43 s
773 MiB
Lightpanda
85
44.3%
0.97 s
40 MiB
Obscura
57
29.7%
1.30 s
39 MiB
Sample agent workload
Metric
Moli
Chromium
CDP ready
34.85 ms
169.37 ms
Episode active p50
33.40 ms
57.13 ms
Peak PSS
102.46 MiB
348.82 MiB
Peak processes / threads
1 / 24
11 / 123
WPT tests
In the current WPT selection used to validate Moli's agent-browser scope, one
full run passed 1.612 million tests.
Moli's performance in Lexbench-Headless-Browser
The full Lexbench-Headless-Browser
corpus contains 1,928 tasks covering raw CDP, 13 pinned automation tools
including Playwright, Puppeteer and Selenium, and web-platform semantics. To
include Kitesurf, which is only available as a remote endpoint, the chart below
uses 1,308 comparable tasks. All browsers use the same task selection rules.
Moli 0.1.1 passed 1,071 tasks, a success rate of 81.88%, ahead of Kitesurf
at 62.08%, Lightpanda at 53.29%, and Obscura at 44.88%; Chrome, the reference
engine, reached 99.85%. Kitesurf ran at k=1, uncovered tasks count as not
passed, and the reproduction conditions of a remote service differ from those
of local binaries. See the benchmark's
five-engine report
for the full results.
Kitesurf is a remote service, so its CPU, memory, and process counts cannot be
measured. The resource comparison therefore covers only the four local
engines. A separate 557-task run includes only work completed by all four.
Moli's median CPU time per task was 100.6 ms and its median peak memory was
92 MiB; Chrome recorded 687 ms and 697 MiB, respectively. Moli used
about 15% of Chrome's CPU time and 13% of its peak memory. See the benchmark's
resource card
for the methodology and full data.
Project scope
Within the agent-browser scenarios defined in its documentation, Moli is ready
for production use and remains under active development.
Its current intentional boundaries include:
No GUI browser, persistent window, GPU compositor, or retained multi-frame
paint architecture.
It does not pursue pixel-for-pixel parity with Chrome or provide
high-fidelity Canvas/WebGL/media playback.
--layout supports software screenshots and native CDP/CLI PDF with embedded fonts
generation, but not every Chrome screenshot or print mode is implemented.
Unsupported protocol paths return explicit errors — Moli never pretends that a
browser action, event, network observation, or visual result occurred.
Unless a file or directory states otherwise, you may use Moli under either the
Apache License 2.0 or the MIT License, at your
option. Separately licensed third-party components and fixtures remain subject
to their own licenses and notices. license-metadata.json
records the machine-readable default, and additional distributable notices are
collected under licenses/.
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Moli 是一款用 Rust 编写、可用于生产环境的无头浏览器，专为 AI 智能体设计。它帮助智能体抓取和提取网页内容、搜索网络，并通过 CLI、CDP、WebDriver Classic 或 WebDriver BiDi 自动执行浏览器任务。