Which tools run in your browser, and which ones call the server?

Most ToolNexus tools execute entirely in your browser. Your input is read, transformed, and rendered locally — nothing leaves the tab. A small number of tools cannot reasonably run client-side (for example, ones that need to execute compiled code in a sandboxed runtime), and those are flagged with a Server-backed badge on their tool card.

This page lists every tool that calls the server, what data is sent, and what we do with it. If a tool is not on this list, it runs in your browser.

Quick summary

Browser-only (the default). Input never leaves your device. We do not log, store, or proxy it. Closing the tab discards it.
Server-backed (flagged with a badge). Input is sent to a ToolNexus-managed sandbox over HTTPS, executed in a short-lived isolated environment, and discarded after the response is returned.

Server-backed tools

The following tools call the server. Tools not in this list run entirely in your browser.

C# Compiler

Why it runs on the server. Compiling and executing C# requires a runtime and an isolated sandbox. Rather than shipping a compiler to every browser session, the source is run on a managed Piston sandbox.
What gets sent. The source code you write in the editor and any standard input you provide. Nothing else from your browser is included.
How long it is kept. The source is sent to the sandbox only for the duration of the run. Captured stdout/stderr is returned to your browser and not persisted server-side.
Sandbox properties. Each run executes in a short-lived isolated container with a fixed CPU/memory budget and a wall-clock timeout, then is discarded.

Python Compiler

Why it runs on the server. Executing Python (and other languages) requires a language runtime and an isolated sandbox. Rather than shipping an interpreter to every browser session, the source is run on a managed Piston sandbox.
What gets sent. The source code you write in the editor, the selected language, and any standard input you provide. Nothing else from your browser is included.
How long it is kept. The source is sent to the sandbox only for the duration of the run. Captured stdout/stderr is returned to your browser and not persisted server-side.
Sandbox properties. Each run executes in a short-lived isolated container with a fixed CPU/memory budget and a wall-clock timeout, then is discarded.

Java Compiler

Why it runs on the server. Compiling and running Java needs a JDK and an isolated sandbox. Rather than shipping a compiler to the browser, the source is run on a managed Piston sandbox.
What gets sent. The source code you write in the editor and any standard input you provide. Nothing else from your browser is included.
How long it is kept. The source is sent to the sandbox only for the duration of the run. Captured stdout/stderr is returned to your browser and not persisted server-side.
Sandbox properties. Each run executes in a short-lived isolated container with a fixed CPU/memory budget and a wall-clock timeout, then is discarded.

PHP Compiler

Why it runs on the server. Executing PHP needs a runtime and an isolated sandbox. Rather than shipping an interpreter to the browser, the source is run on a managed Piston sandbox.
What gets sent. The source code you write in the editor and any standard input you provide. Nothing else from your browser is included.
How long it is kept. The source is sent to the sandbox only for the duration of the run. Captured stdout/stderr is returned to your browser and not persisted server-side.
Sandbox properties. Each run executes in a short-lived isolated container with a fixed CPU/memory budget and a wall-clock timeout, then is discarded.

What "browser-only" actually means

Browser-only tools rely exclusively on JavaScript or WebAssembly running in your tab. Concretely:

Your input never touches a ToolNexus server.
There is no analytics call that ships the payload as part of an event.
The page can run offline once it has been loaded.
Refreshing the tab discards anything you typed unless the tool has opted in to local storage (in which case the tool description says so explicitly).

If you spot a tool that behaves like it is talking to the server but is not on this list, please file a feedback report — that is a documentation bug we want to fix.

Privacy Policy — covers what the rest of the site (analytics, account features) does with data.
FAQ — short answers to common questions.
Feedback — tell us if a tool should be browser-only but is not, or vice versa.