Run in the browser
Run the whole VOLT stack inside one browser tab, with nothing installed and the workspace kept in the browser.
Run in this browser starts VOLT's server and a cluster daemon inside the tab you're looking at. They're the same programs a self-hosted deployment runs, compiled to WebAssembly, and the tab becomes its own backend: you upload trajectories, run analyses and open results without a server or anything installed.
Use it to try VOLT or for short sessions on one machine. For regular work on your own computer, the desktop app runs the same thing with storage the browser can't clear.
Start it
Open a VOLT web client and choose Run in this browser on the Connect to a server screen (/connect). A link to /connect?run=browser does the same in one step, as long as that browser isn't already connected to a server.
The first time, the page reloads once. It has to be served through VOLT's service worker before it can start the stack.
Starting VOLT in this browser lists the startup phases: Start API server, Provision workspace and Start compute daemon. Show log opens the stack's output.
The dashboard opens, signed in to the workspace's local account.
On the first start, provisioning creates the local account, a team and a cluster, then waits up to two minutes for the daemon to connect. After the app opens, a default set of analysis plugins installs from the plugin registry in the background. Any that fail to install are tried again on the next start.
What runs in the tab
- The server and the daemon run in workers of the page and reach each other over a loopback network inside the tab. The service worker relays the page's
/apiand/socket.iorequests to the server, so the client talks to it as it would to a remote one. - Databases are SQLite (the server's and the daemon's) and DuckDB (which analyses query), both in their WebAssembly builds.
- Plugins run their
wasm-wasm32builds. The daemon reports its platform aswasm-wasm32, and installs ask the registry for that build. - Python is CPython compiled to WebAssembly (Pyodide), available as
python3to the daemon and to plugins written in Python. - Notebooks open in VOLT's own notebook editor, with their kernels running in the page. See Notebooks.
Where your workspace is stored
Everything lives in the browser's origin private file system (OPFS) for the address you opened VOLT at:
| Entry | Holds |
|---|---|
volt-local-stack.json | The provisioning state: local account, team and cluster IDs, the stack's generated secrets, the default plugin installs |
volt-server/, .volt-server-sqlite/ | The server's files and database |
volt-daemon/, .volt-daemon-sqlite/ | The daemon's files and database: trajectories, analysis results, installed plugins |
volt-notebooks/ | The notebook kernels' file system: one virtual environment and working directory per workspace |
The browser's local storage also keeps a flag that this address runs its own VOLT, so the next visit starts it again.
The workspace persists across reloads and browser restarts. It belongs to that address, browser and profile: another address, another browser or a private window starts a separate, empty workspace.
The browser can delete this storage. Clearing the site's data removes the workspace, a private window discards it when it closes, and the browser may evict it when the disk runs low, since VOLT doesn't request persistent storage. Use the desktop app or a server for work you need to keep.
Limits
One tab per address
Only one tab of an address can run the stack, because its workers hold the workspace's files open. A second tab stops with:
VOLT is already running in another tab of this browser. Close it, or use that tab.
Closing the tab stops the server and the daemon, and anything running stops with them.
Browser requirements
The stack needs service workers, Web Locks, the origin private file system and SharedArrayBuffer. SharedArrayBuffer needs a cross-origin isolated page, which the service worker provides by serving the page with Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: credentialless; the browser has to support both. Browsers only allow service workers on secure origins, so the page must be served over HTTPS or from localhost. A client opened at a plain-HTTP LAN address can't run it.
When something is missing, startup stops with one of these:
| Message | Cause |
|---|---|
| This browser lacks what the local backend needs (service workers, Web Locks and the origin private file system). | One of those APIs is unavailable, often because the page isn't on HTTPS or localhost. |
| This browser cannot isolate the page, which the local backend needs (SharedArrayBuffer). | The page still wasn't cross-origin isolated after reloading through the service worker. |
One user, one machine
A browser workspace runs in local mode: there are no other accounts, and the app hides team management, invitations, roles and sign-out (see Deployment modes). Its only cluster is the tab itself, so the Clusters pages and Connect new cluster aren't offered.
Plugins need a wasm-wasm32 build
A plugin runs in the browser only if it publishes a wasm-wasm32 build. Installing one that doesn't fails, because the registry has no build for this platform. The plugin catalog lists the published plugins.
Python runs under Pyodide
Python is a guest of the page, so it works differently from Python on a machine:
- There's no
subprocessand no threads. python3 -m pip installtakes Pyodide's builds of packages with native code (numpy, pandas, pyarrow, scikit-learn and others) and pure-Python wheels from PyPI. The first install of a package downloads it from Pyodide's CDN.requestsreaches the backends through the service worker's relay.pip install voltsdkinstalls the build of the Python SDK that ships with this client, not the one on PyPI. The SDK'sSpatialAssemblerisn't available, since its native extension has no Pyodide build.
What needs the network
Installing plugins downloads them from the plugin registry, and installing Python packages downloads them from Pyodide's CDN or PyPI.
Leave or reset
If startup fails, the screen offers Try again and Connect to a server instead. The second one stops running VOLT in this browser and opens /connect.
To delete the workspace and stop running VOLT at this address, clear the site's data in your browser's settings. This removes everything in the table above. The next visit shows the web client as usual, and Run in this browser starts a new, empty workspace.