Replay server responses from a HAR file
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Replay server responses from a .har file.

Useful if…

  • …you want to develop offline and your development server isn't local
  • …your development server is very slow and you want to go faster
  • …you are developing against an API with rate limits

It works by starting a proxy server and serving content from a previously saved .har file overlayed with files from your local system, configurable with mappings.


npm install -g server-replay


You need to have a .har file, run server-replay, and then set up your browser to use it as a proxy.

A .server-replay.json in the current directory is used by default if no config option is given.

server-replay [options] <.har file>

  -c, --config  The config file to use
  -p, --port    The port to run the proxy server on  [default: 8080]
  -d, --debug   Turn on debug logging

See the Setup section for details on creating .har file and using the proxy in your browser.


The config file is a JSON file (plus // comments) with the following properties:

  • version – currently 1
  • mappings – Maps from URLs to file system paths. It is an array of {match, path} objects. match is a string or regex, and path is a string. path can contain $n references to substitute capture groups from match.
  • replacements – Replaces strings in the body of textual content. It is array of {match, replacement} objects. match is a string, regex or variable, and replacement is a string or variable. replacement can contain $n references to substitute capture groups from match.

Full example:

    "version": 1,
    "mappings": [
            "match": {"regex": ".*\\/static\\/(.*)"},
            "path": "./public/$1"
    "replacements": [
        // For JSONP requests where callback name is randomly generated
            "match": {"var": "entry.request.parsedUrl.query.callback"},
            "replace": {"var": "request.parsedUrl.query.callback"}
        // Proxy only works over http
        {"match": "https", "replace": "http"}


The types mentioned above take the following forms:

  • string – a plain string. Example: "something".
  • regex – an object with a regex property, and an optional flags property. If you don't provide the flags property, unlike JavaScript, the regex has the global flag set. Example: {"regex": "user\\/([a-z]+)", "flags": "ig"}
  • variable – an object with a var property which contains a path to a value. See below for the available variables. Example: {"var": "request.parsedUrl.query.q"}


  • request – the Node request object with the addition of a parsedUrl property, containing the parsed url and query.
  • entry – the HAR entry that is being used to respond to this request. It also has a parsedUrl property, and an indexedHeaders property which maps each header name to it's value(s).


Getting a .har file

The easiest way is with the Chrome DevTools. In the Network panel disable the cache, refresh the page and interact with the page to generate the network requests that you want to capture. Then right click and select "Save as HAR with Content".

Creating a .har file

Note: Extensions such as AdBlock and Ghostery interfere with the recorded responses. Be aware of this and, if necessary, disable them before loading the page.

Browser proxy configuration


Launch with the --proxy-server argument:

/Applications/Google\\ Chrome --proxy-server=


Preferences > Advanced > Network > Settings… > Manual proxy configuration

Firefox proxy settings


Copyright 2015 Adobe Systems Incorporated

This software is licensed under the Apache License, Version 2.0 (see LICENSE file).