CSP Header Validator — Content Security Policy
Parse and validate Content-Security-Policy headers with directive analysis and security warnings.
How it works
- 1Paste or type your text in the input field
- 2Click "Process" — processing happens in your browser
- 3Copy the result or download as a text file
What to do next
About CSP Header Validator
CSP Header Validator is a web utility tool that runs in your browser. Parse and validate Content-Security-Policy headers with directive analysis and security warnings. The page you are reading is the same workspace you will use to do the work: pick a file or paste your input, choose the options that matter to you, and the tool produces the result on your device.
If you fit any of these descriptions, CSP Header Validator should slot cleanly into your workflow: site owners auditing pages; teachers building resource lists; analysts pulling lightweight reports. The tool keeps the controls focused on what matters for each of these use cases.
The execution path is auditable from the page itself: open developer tools, switch to the Network tab, run a job. The requests you see are static-asset GETs for the engine and the page resources. The actual work is JavaScript code running against the bytes already in your tab's memory.
Architecturally, CSP Header Validator is a single-page client. The processing layer is standard browser APIs; the UI is a thin React shell on top. Inputs flow through the engine and the output is returned to the browser as a Blob you can save or copy. The 0 MB cap is the only hard limit and it exists to keep memory usage stable on every device.
Most people land on CSP Header Validator via a search at the moment they actually need the tool. That shapes the design: the page is a single screen with the input on one side, the controls in the middle, and the result on the other, so a first-time visitor can complete the job without reading documentation.
Even on its own, CSP Header Validator composes well with the rest of your toolkit. The output is a standard web utility file that opens in any program that handles the format, so the result of one run can become the input to whatever step you use next.
The download is delivered as a clearly named file the moment processing completes — no email link, no "your result will be ready in 5 minutes" queue, no expiry timer. The file is generated in your browser and saved by your browser's normal download flow.
The only practical limit is the 0 MB per-file ceiling, which keeps the tool responsive across a wide range of devices. Run the tool ten times in a row, run it ten thousand times — it behaves the same way and produces the same quality of result.
The transformation in CSP Header Validator is deterministic — the same input plus the same options produces the same result every run. That predictability matters when the result has to match an upstream specification or be reproducible later.
Some background on the design choices behind CSP Header Validator: every option you see on the page is there because a real workflow needs it, and every option that is not shown has been deliberately omitted to keep the common case fast. The bias is toward minimal-but-complete.
If you want to get the most out of CSP Header Validator, three small habits help. Drag-and-drop is faster than the file picker once you get used to it. The keyboard shortcut for downloading the result is whatever your browser uses for "save link as," because the result is a normal download. And if you are working on a sensitive file, processing in an Incognito or Private window is a good extra layer — it leaves no trace in browser history when the tab closes.
If CSP Header Validator appears to hang, the engine is almost certainly still working — large inputs simply take longer to process inside a browser than they would on a server with multi-core scheduling. For inputs near the 0 MB cap, give it up to a minute on a typical laptop before assuming something is stuck.
As a single-page tool, CSP Header Validator stays focused on one web and productivity utility step. Multi-step workflows are composed by chaining adjacent tools — each tool produces a standard file the next one can read directly, so a longer pipeline is just a sequence of short tab-and-tab visits.
CSP Header Validator is intentionally narrow in scope so the common case is fast and the result is predictable. If you ever need a variation it does not cover, browse the rest of the catalog — there is a good chance an adjacent tool already exists, and switching between tools is just a matter of opening another tab.
How it works
- 1Reach the CSP Header Validator page in your browser to begin.
- 2Select the web utility file you want to process — drag-and-drop and the file picker both work.
- 3Tweak the controls if the defaults are not quite right for your input. The options are kept short and labelled in plain language.
- 4Hit the run button. standard browser APIs does the work in your browser tab.
- 5Download the result. The file is generated in your browser and saved through your normal download flow.
- 6Repeat the process for additional inputs whenever you need to. The page stays loaded, so subsequent runs are quick.
Common use cases
- Plan content without paying for a SaaS dashboard using CSP Header Validator.
- Sanity-check a webhook response while debugging.
- Run a one-off check during a meeting without context-switching.
- Preview how a result looks before deploying it.
- Compare two product variations side by side.
- Audit a marketing page before launch.
- Create a placeholder image for a wireframe.
- Validate a setting before circulating it to a team.
FAQ
What is CSP?
Content-Security-Policy is an HTTP header that controls which resources a browser can load for your page.
What is checked?
The tool parses directives and warns about unsafe-inline, unsafe-eval, wildcards, HTTP sources, and missing default-src.
Does it test my site?
No — paste your CSP header value for offline analysis. It does not fetch your site headers.
Private?
Yes — parsing runs locally.
Report-only mode?
Content-Security-Policy-Report-Only headers have the same syntax and can be analyzed with this tool.
Nonce and hash?
Nonce and hash-based policies are parsed and displayed but not validated for correctness.
What is the maximum file size for CSP Header Validator?
Inputs are capped at 0 MB per file, which keeps memory usage stable across phones, tablets and older laptops. You can run CSP Header Validator as often as you need; every run produces a full-quality result.
Will I notice a difference in the output from CSP Header Validator?
CSP Header Validator is built to preserve quality wherever the underlying web utility format allows it. Operations that are mathematically lossless (e.g. structural transformations, lossless re-encoding) round-trip with no perceptible change. Operations that involve a lossy codec inevitably introduce small artefacts at the byte level, but the defaults aim at the sweet spot where output looks or sounds the same to a normal viewer or listener while still being meaningfully smaller or faster than the input.
Is CSP Header Validator keyboard accessible?
CSP Header Validator uses native HTML controls wherever possible, which means keyboard navigation, focus rings, and screen-reader labels work the way the platform expects. The drop zone accepts files via the keyboard-accessible file picker as well as drag-and-drop, and result downloads use standard browser download flows. If you spot an accessibility gap, Favtoo treats it as a bug worth fixing.
Does CSP Header Validator work on a phone or tablet?
CSP Header Validator runs in any modern mobile browser — Safari, Chrome, Firefox and the in-app browsers in most messaging apps all support the underlying APIs. Performance depends on the device: a recent phone handles typical inputs nearly as fast as a laptop, while older devices may take a few seconds longer near the 0 MB ceiling. The interface lays out cleanly on small screens, so you do not need to pinch-zoom to see the controls.
Are there any restrictions on using CSP Header Validator at work?
CSP Header Validator can be used for personal and commercial work alike — there is no separate "business" licence to purchase. The output you generate is yours to use however you want, including in client deliverables, internal documents, or commercial products. Favtoo's only ask is fair, individual use; the tool is not designed to be embedded as a backend service or wrapped behind an API for resale.
What input formats are supported by CSP Header Validator?
The accepted formats are listed in the upload area on the tool itself. If your input is in a format that is not directly supported, convert it first using one of Favtoo's converter tools — every Favtoo converter outputs a file that is a clean input to the next tool in the chain.
Do I need to install anything to use CSP Header Validator?
No installation is needed. CSP Header Validator runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use CSP Header Validator on any computer you have temporary access to without leaving anything installed on it.