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brom is a configurable CLI for recording HTTP transactions and improving security practices, designed for use in local environments and CI tools. Get your headers in order before deployment.

Table of Contents


npm install -g brom


This repository has a built-in brom config, so just clone, install, and run to see brom in action. You'll need Node 6.4.0 or later, and npm.

  1. Clone this repository locally
  2. In the root directory, npm install
  3. npm install -g brom
  4. brom
  5. brom will open the GUI in your default browser automatically. Open a second tab and navigate to localhost:9999 to start making/recording requests.


brom <server.js> <port> [OPTIONS]

brom records HTTP transactions, generates configurable warnings, and provides you with detailed information on both requests and responses. By default, it opens a second browser tab to aid inspection with by-header breakdowns and a variety of filters.

If you'd rather go without the GUI and just get the data:

brom -g --write-dir=brom

writes all transactions from a given session to a timestamped file, assessments included.

brom recording sessions operate through two modes (which can run simultaneously):

Interactive mode (on by default)

brom proxies your server, recording HTTP transactions as they stream through, and injecting a script into HTML documents to record third-party AJAX calls.

Automated mode (Express.js only)

brom -a

brom traverses Express application structures to identify all registered routes and their supported methods, sending dumb requests to each one. Great for check-ins and (with a bit of configuration) build processes.

Rule syntax

While brom comes with smart defaults for assessing header practices, the security needs of your application are unique. brom provides a rule syntax to allow you to create your own rules. Here's a built-in rule:

  id: 'no-x-powered-by', // linter name
  header: 'x-powered-by', // used to organize warnings in GUI
  when: (headers, type) => type === 'response', // when to run this rule
  expect: headers => !headers['x-powered-by'], // pass/fail statement
  fail: {
    message: `The X-Powered-By header advertises unnecessary
              details about your server, and should not be sent.`

The id field is meant to uniquely identify rules, allowing you to tell brom what rules to skip, and what rules should halt a build process on failure. See Configuring brom.


Your when callback helps brom decide on which transactions to run which tests. brom passes it a headers object, with each header from an HTTP message, and a type string to identify the message as a request or response.

For instance, when Content-Security-Policy headers only matter on HTML responses:

  // ...
  when: (headers, type) => (
    type === 'response' &&
  // ...


The expect callback represents your actual requirements: brom takes the truthiness of the return value to indicate whether or not the transaction failed this rule. It passes the same headers object as then when callback.

Here's the expect callback for the same rule, to confirm that a CSP has been provided:

  // ...
  expect: headers => headers['feature-policy'],
  // ...

Configuring brom

brom needs, at minimum, to know what local port to proxy to, and with many settings it also needs a path to your server. If you'd rather just type brom, provide a brom.config.json in your project's root directory.

  "server": "demo/server.js",
  "port": 3000

All CLI flags can be preconfigured here as well. In a defaults key provide settings matching the longform of any flag. These settings will always be overridden by flags and arguments passed directly to the CLI:

  "server": "demo/server.js",
  "port": 3000,
  "defaults": {
    "automated": true,
    "https": true,
    "preserve-caching": true,
    "write-dir": "brom-history"

brom uses two lightweight servers to operate (a proxy for inspecting transactions, and a server for aggregating results from multiple sources). These operate on ports 9999 and 7913 respectively, but you can move them where you like:

  "proxy-port": 3001,
  "results-port": 3002

Some rules may not be relevant enough to your application to keep getting reminders. To turn these off in your config, add an array of rule ids to ignore:

  "ignore-rules": [

Conversely, to tell brom to exit with a nonzero status code on certain rules, add them to a "halt-on" key:

  "halt-on": [

If you've configured your server to run HTTPS locally, brom needs to serve HTTPS too. brom can piggyback off of the same key and certificate. Add relative paths to the key and certificate, and fire up brom with the --https flag.

  "https": {
    "key": "../application/server.key",


When writing rules, some headers are tougher to parse, so brom provides a simple set of header parsers.


Parses a CSP value and returns an object, with each directive name as a key and each directive value as an array of strings.

The value string must be the actual header value (everything after the :).


Alias for brom.contentSecurityPolicy.

brom.csp("default-src 'self'; img-src *; script-src");

// {
//   'default-src': ['\'self\''],
//   'img-src': ['*'],
//   'script-src': ['']
// }


Parses a Feature Policy value and returns an object. Each key is a feature, and its value an array of whitelisted domains.

The value string must be the actual header value (everything after the :).


Alias for brom.featurePolicy.

brom.fp("vibrate 'none'; geolocation 'none'");

// {
//   vibrate: ['\'none\''],
//   geolocation: ['\'none\'']
// }


Parses a Cookie value and returns an array of cookies. The cookie name and value are separated into name and value keys.

The value string must be the actual header value (everything after the :).

brom.cookie('hello=world; foo=bar;');

// [
//   { name: 'hello', value: 'world' },
//   { name: 'foo', value: 'bar' }
// ]


Parses a Set-Cookie value and returns an object. The cookie name and value are separated into name and value keys; the rest are separated into key-value pairs (non-value directives like "Secure" are set to true).

The value string must be the actual header value (everything after the :).

brom.setCookie('a=b; Path=/; Max-Age=0; Secure; HttpOnly');

// [
//   {
//     name: 'a',
//     value: 'b',
//     Path: '/',
//     'Max-Age': '0',
//     Secure: true,
//     HttpOnly: true
//   }
// ]


Returns a new object, with Content-Security-Policy, Feature-Policy, Set-Cookie, and Cookie headers parsed. All other headers are left unchanged under a single headers key.

const parse = require('brom');
  'Content-Security-Policy': "default-src 'self'; img-src *; media-src; script-src",
  'Feature-Policy': "vibrate 'none'; geolocation 'none'",
  'Cookie': 'hello=world; foo=bar;',
  'Set-Cookie': 'a=b; Path=/; HttpOnly;',
  'Content-Type': 'text/html; charset=utf-8',
  'Content-Length': '7913'

// {
//   contentSecurityPolicy: {
//     'default-src': ['\'self\''],
//     'img-src': ['*'],
//     'media-src': ['', ''],
//     'script-src': ['']
//   },
//   cookies: [
//     { name: 'hello', value: 'world' },
//     { name: 'foo', value: 'bar' }
//   ],
//   featurePolicy: {
//     vibrate: ['\'none\''],
//     geolocation: ['\'none\'']
//   },
//   setCookie: [
//     {
//       name: 'a',
//       value: 'b',
//       Path: '/',
//       'Max-Age': '0',
//       Secure: true,
//       HttpOnly: true
//     }
//   ],
//   headers: {
//     'Content-Type': 'text/html; charset=utf-8',
//     'Content-Length': '7913'
//   }
// }

The headers object you pass in can contain any number of headers. Each key should be a header name (everything up to the :), and its corresponding value the remainder of that header string.

The only exception to this rule is your Set-Cookie header, which may be either a string (representing a single cookie) or an array of strings representing multiple cookies.


Is brom for Express only?

Yes and no: brom hasn't been tested extensively on non-Node backends, but the interactive-mode flow has no interaction with or awareness of your server, other than the port to proxy to.

However, brom's automated mode is designed explicitly for Express servers (off by default), and you'll need to turn off autostart (add an -m flag) to tell brom not to look for a server file. Start up your server as its own process, and run brom <port> -m.

Does brom support HTTPS?

As long as you've set up local HTTPS before, brom can piggyback off of the same certificate. See the Configuration section for more details on configuring HTTPS.

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