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X-Content-Type-Options / MIME-Sniffing Header Builder

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Build the X-Content-Type-Options: nosniff response header (there is only one valid value) with a plain-English explanation of the MIME-sniffing attack it prevents, validate a pasted header value, and check how risky a given Content-Type is to serve without it

X-Content-Type-Options only ever has one correct value, nosniff, so this tool's real job is explaining what it does rather than helping you build a string. It tells the browser to trust the declared Content-Type instead of guessing a response's real type from its bytes, which matters because a browser that decides an oddly-typed response looks like HTML may render or execute it. Paste a header value you found on a real response to check it's actually nosniff and not a typo, or enter a Content-Type to see how risky it is to serve without this header based on well-known MIME-sniffing attack patterns. It's a small header, but automated scanners like Mozilla Observatory and securityheaders.com flag its absence constantly, and it's a natural sibling to the site's other security header builders.

x-content-type-optionsnosniffmime-sniffingheadershttpsecurity

How to use X-Content-Type-Options / MIME-Sniffing Header Builder

  • 1.Copy the fixed X-Content-Type-Options: nosniff header, there's nothing to configure since it only has one valid value.
  • 2.Paste a header value or line you found on a real response to confirm it's exactly "nosniff" and not a typo the browser silently ignores.
  • 3.Enter a Content-Type to see a risk rating for serving it without this header, based on known MIME-sniffing attack surfaces.

Frequently asked questions

Why does this header only have one value?
nosniff is the entire spec. Anything else, including a typo, an empty string, or a value like "deny" copied from a different header, is silently ignored by the browser, which is exactly why the tool includes a checker for pasted values.
Is my site safe just by adding this header?
It closes one specific class of MIME-sniffing attack, but it's not a substitute for actually setting correct Content-Type headers on every response, sanitizing user-generated content, and using Content-Security-Policy for broader script-injection protection.
How is the Content-Type risk rating calculated?
It's a heuristic lookup against well-known MIME-sniffing attack surfaces (text/plain and application/octet-stream are high risk, most image and media types are low risk), not a live scan of an actual HTTP response, so treat it as general guidance rather than a security audit of your server.
Does this make a network request?
No, everything is computed locally from the header value or Content-Type you provide. It doesn't check your actual server's real response headers.

Use via API, SDK, or MCP

cURL# Free: 1,000 req/day · Pro: 10,000 req/day
curl -X POST https://api.utilix.tech/v1/tools/x-content-type-options-builder \
  -H "Authorization: Bearer utx_live_..." \
  -H "Content-Type: application/json" \
  -d '{}'

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