What is CSP Builder?
CSP Builder is a free, browser-based tool in the Developer Tools suite. Compose a Content-Security-Policy directive by directive. Add sources for default-src, script-src, style-src and more; toggle upgrade-insecure-requests and block-all-mixed-content. Output as HTTP header or meta tag.
The headline benefit: build a content-security-policy header with a clean ui.
Unlike most online tools that upload your file to a server, process it, and send it back, CSP Builder runs entirely in your browser. Open DevTools → Network while using it and you'll see zero file-upload requests — only static assets (JavaScript, CSS, fonts) load. Your data never leaves your device.
Why use this csp builder?
Three reasons EasyFileKit's CSP Builder stands out from the crowd:
- **Private by design** — all processing happens locally via JavaScript and WebAssembly. No server ever sees your input.
- **Instant** — no upload wait, no queue, no server round-trip. Results appear the moment you act.
- **Free & unlimited** — no accounts, no watermarks, no daily caps. Use it as many times as you like.
How to use CSP Builder — step by step
Here's the complete walkthrough. Everything happens instantly in your browser:
- **Step 1.** Add or edit directives — default-src, script-src, style-src and more.
- **Step 2.** Toggle upgrade-insecure-requests and (optionally) report-uri.
- **Step 3.** Copy either the HTTP header or the meta tag version.
That's it. No sign-up, no upload bar, no waiting. If something doesn't work as expected, check the FAQ below.
Common use cases for CSP Builder
People reach for CSP Builder in a few recurring situations:
- When you need the result **now** and can't wait for a server-based tool to upload, queue, and process your file.
- When your file is **private or sensitive** — financial documents, personal photos, medical PDFs — and you don't want it travelling across the internet.
- When you're on a **slow or metered connection** — uploading a 50 MB file just to compress it makes no sense when the same work can happen locally.
- When you've hit the **daily limit or paywall** on another "free" tool site.
Privacy: what actually happens to your data
This is the single most important point about CSP Builder, so it deserves its own section.
When you use this tool, your input is processed by JavaScript running in your browser tab. The code is downloaded once (cached afterwards) and executes locally on your CPU. At no point is your file, your text, or your input data transmitted to any server.
You can verify this yourself in under 30 seconds:
- Open CSP Builder in your browser.
- Press F12 to open DevTools.
- Switch to the Network tab and tick "Disable cache".
- Use the tool — drop a file, type text, whatever the tool needs.
- Watch the Network log. You'll see only static assets (JS, CSS, fonts, icons). No request contains your data.
This isn't a setting you toggle or a promise in a privacy policy — it's how the tool is architecturally built. There is no upload endpoint to call.
Frequently asked questions about CSP Builder
Q: What's the difference between the header and meta tag?
A: The HTTP header is set by your server and is recommended. The meta tag works for static sites without server config — but some directives (like frame-ancestors) only work in the header.
Q: What does 'self' mean?
A: Same-origin — only resources from the current site are allowed. Always start with default-src 'self'.
Q: Why is unsafe-inline bad?
A: It allows inline scripts and styles, which weakens CSP's XSS protection. Move inline scripts to external files where possible.
Q: Is my policy uploaded?
A: No. The header is built locally.
CSP Builder: EasyFileKit vs server-based tools
Most "free" online tools that do what CSP Builder does follow the same model: you upload your file to their server, they process it with a backend script, then they send the result back. Here's the honest comparison:
| | EasyFileKit | Server-based tools |
|---|---|---|
| **Your file leaves your device?** | Never | Yes, uploaded to a server |
| **Speed** | Instant (no upload) | Slower (upload + queue + download) |
| **Privacy** | Complete | Your file is on someone else's computer |
| **Cost** | Free, unlimited | Often capped or "premium" gated |
| **Works offline** | Yes (PWA) | No |
Server-based tools aren't evil — they exist because some tasks genuinely need heavy backend compute. But for everything CSP Builder does, client-side processing is strictly better for you.
Under the hood: how CSP Builder works
CSP Builder is built with modern browser APIs. Depending on what it does, it may use:
- **Canvas API** — for image manipulation (pixel-level access, filters, resizing).
- **Web Crypto API** — native, hardware-accelerated cryptography (AES-GCM, SHA-256, PBKDF2) for any encryption or hashing.
- **pdf-lib / pdf.js** — fully client-side PDF creation and rendering.
- **MediaRecorder API** — for capturing screen, audio, and video.
- **WebAssembly** — for heavy codecs (image compression, media processing).
All of these run inside your browser's sandbox. They cannot access your filesystem (beyond files you explicitly choose), cannot make network requests with your data, and cannot run persistently in the background.
Pro tips for getting the most out of CSP Builder
- **Bookmark the tool** — it works offline once cached, so you can use it even without a connection.
- **Install EasyFileKit as a PWA** — open the browser menu and choose "Install app" for a standalone window and offline access.
- **Use it on mobile** — every tool is fully responsive and works on phones and tablets, not just desktops.
- **No file size anxiety** — because nothing uploads, you can process large files that server-based tools would reject or charge for.
Try CSP Builder now
The tool is right above this article — scroll up and start using it. No sign-up, no upload, no limits.
If you found CSP Builder useful, explore the rest of the Developer Tools suite — there are more tools that work the same private, instant, free way. And if you have a question that isn't covered in the FAQ above, the About page has our contact email.