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- No default-src - every directive you don't set explicitly falls back to the browser's permissive default.
Fallback for every fetch directive you do not set explicitly. Set this first, then tighten individual directives.
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(Dokumentasjon på engelsk)
What it does
The CSP Builder assembles a Content-Security-Policy (CSP) header interactively. Instead of hand-writing a long semicolon-separated string, you toggle the directives you want, add sources to each one, and watch the finished header build itself in real time. A live security score penalizes unsafe sources ('unsafe-inline', 'unsafe-eval', data:, http:, *) and a missing default-src, so you can see the cost of every shortcut before you ship it.
It also parses: paste an existing CSP header into Import and it becomes an editable policy you can tighten and re-export. Everything runs 100% client-side - no header you paste is ever sent to a server.
How to use it
- Optionally paste an existing policy into Import existing header and press Parse to load it.
- Flip the switch on each directive you want (
default-srcfirst - it is the fallback for everything you leave unset). Click a directive row to expand its description and sources. - Add sources per directive: click a preset chip (
'self','none','strict-dynamic',https:, …) or type a custom URL /'nonce-…'/'sha256-…'value and press Add. Red chips are risky sources - hover one to see why. - Watch the security score and warning list at the top, then Copy the assembled header (or Copy share link to send the exact policy to a teammate).
Examples
A strict starter policy
default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'none'Add a CDN with a nonce, allow data-URI images
default-src 'self'; script-src 'self' https://cdn.example.com 'nonce-r4nd0m'; img-src 'self' data:; object-src 'none'; base-uri 'self'; frame-ancestors 'none'; upgrade-insecure-requestsThe same policy after importing it back - Parse returns the exact editable map, and building again reproduces the header byte-for-byte.
Good to know
- Set
default-src. Directives you leave unset fall back to it; without it, the browser’s permissive default applies and your policy has holes. - Risky sources cost score, not correctness:
'unsafe-inline'(-20),*(-20),'unsafe-eval'(-15),data:/http:(-10 each). Prefer nonces or hashes over'unsafe-inline'. - Delivery matters: send the header from your server (or CDN/Worker).
frame-ancestorsis ignored inside a<meta>tag. - Round-trip safe: build → parse → build reproduces the identical string, so share links and re-imports are lossless. Directives with no sources are omitted (a valueless directive is invalid CSP).
- Private: runs entirely in your browser - safe for policies covering internal domains.
- Related tools: PII Redactor, Password Strength Analyser, Defang/Refang.