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    Generate Content-Security-Policy headers from inline script and style hashes

    When running things like Gatsby or Gridsome, the initial state is stored inside a <script> tag. Modern browser content security policies don't like inline scripts or styles, so to get around it you need to add either a cryptographic nonce or a cryptographic hash of each script. A nonce is out of the question, because you can't update it for each load.

    This package generates a crypographic hash (SHA-256) of all inline scripts and styles in each HTML file, and adds it to the _headers file along with other policies of your choice.

    Netlify lets you add a Content-Security-Policy header in your netlify.toml. This will overwrite values inside _headers, so don't do that.

    If you have an existing _headers file, this will append to the existing file. Just make sure the file ends on a newline, and it should work fine.


    Install netlify-plugin-csp-generator with your favourite package manager:

    yarn add netlify-plugin-csp-generator
    npm install netlify-plugin-csp-generator

    In your netlify.toml file, add an additional plugin:

    package = "netlify-plugin-csp-generator"
      buildDir = "dist"
        defaultSrc = "'self'"


    • buildDir is the path for the publish directory in Netlify: buildDir example
    • exclude is an array of paths you don't want to include. It defaults to an empty array.
    • disablePolicies is an array of policies to never include. Files that need these rules will probably be taken from defaultSrc instead by your browser.
    • disableGeneratedPolicies is an array of policies never to generate. Use this to turn off default policies but still allow the key in netlify.toml.
    • reportOnly generates headers with Content-Security-Policy-Report-Only instead, which is useful for testing.
    • reportURI/reportTo sends violations to a given endpoint. See Reporting violations for more information.
    • generateForAllFiles lets you generate headers for non-HTML files. See Non-index.html files for more information.


    You can use the following policies:

    Add them under the [plugins.inputs.policies] object in your netlify.toml file, with your specified value in quotes.

    You can use CSP headers not in this list too - simply use the name in camel case and it will be added.

    Inline styles

    When using Vue and derivatives (like Gridsome), you may want to use v-show on things. This adds an inline style of display: none;, which is forbidden by CSP Level 3. To prevent this throwing an error, you need to add 'unsafe-hashes' to your styleSrc policy. The sha-256 hash is generated automatically.

    package = "netlify-plugin-csp-generator"
      buildDir = "dist"
        defaultSrc = "'self'"
        styleSrc = "'unsafe-hashes'"

    What is generated

    If you have defined a policy in your netlify.toml file, this will be added to all files.

        defaultSrc = "'self'"
        scriptSrc = "'self'"
      Content-Security-Policy: default-src 'self'; script-src 'self' *;

    If a file includes a <script> or <style> tag with content, this file path will have the hash added:

      Content-Security-Policy: default-src 'self';
      Content-Security-Policy: default-src 'self'; script-src 'sha256-RFWPLDbv2BY+rCkDzsE+0fr8ylGr2R2faWMhq4lfEQc=';

    If a file has any inline styles, these will be hashed:

    <div style="display:none;"></div>
      Content-Security-Policy: style-src 'unsafe-hashes' 'sha256-0EZqoz+oBhx7gF4nvY2bSqoGyy4zLjNF+SDQXGp/ZrY='

    Non-index.html files

    Generally, routes are generated with an index.html file, like /some/file/path/index.html. However, sometimes you need to handle HTML files that aren't called 'index', for example 404.html in Nuxt.

    These are generated as wildcard links and are placed above the non-wildcard paths in your _headers file (for specificity):

      Content-Security-Policy: default-src 'self'; script-src 'sha256-Qb2XxXiF09k6xbk2vTgHvWRed+mgYYGzFqZ6dShQVA0=';
      Content-Security-Policy: default-src 'self';

    Any matching wildcard URL has the hashes joined together - for example, if you have a 404.html and a 500.html with scripts/styles, all the hashes will be merged together under /*.html.

    In general, it is better to generate /path/index.html rather than /path.html.

    Using the generateForAllFiles setting, you can generate route keys that use /* instead of /*.html. Be careful, this will send Content-Security-Policy headers for every file type (i.e. .js, .css, etc) which is redundant as per the spec.

    Reporting violations

    The Content-Security-Policy specification allows for reporting violations to a URL - you can read more about it on MDN.

    This is useful for testing and checking directives.

    To set the header to report only, set reportOnly = true in your netlify.toml alongside your policies.

      reportOnly = true
      reportURI = "/report-csp-violations-to-this-uri"


    1. Setting reportOnly to true will NOT enforce your policy
    2. You need to add reportURI too

    Using the report-to directive

    The reportURI is deprecated in CSP Level 3 in favour of report-to. To use the report-to directive, set the reportTo value to the group name as defined in the Reporting-Endpoints header that you also need to set.

      reportOnly = true
      reportTo = "csp-violations-group"
    1. You can include reportURI and reportTo without setting reportOnly = true, and the policy WILL be enforced and errors will also be reported
    2. You can set both the reportTo and reportURI directives - this is recommended to ensure maximum compatibility

    Help it's all broken!

    Oh, you. Chances are your browser console is screaming at you, and the network tab is showing a lot of (blocked:csp) errors.

    See our list of example policies to get started.

    Don't unsafe-inline everything, because that will make CSP redundant. If in doubt, ask Google, Stackoverflow, or create a Github issue (in that order).


    If you found this plugin useful, or are just feeling nice, feel free to donate!

    Buy me a coffee


    npm i netlify-plugin-csp-generator

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