Major Configuration File Formats – Developers Need to Know

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Configuration files are the source of the initial settings and parameters required by computer applications and even operating systems. These files are generally written using the “ASCII Coding” system and are a store for data that pertains to a username, software applications or even specific filenames.

Configuration files are mainly used for server level processing, operating system setting, and software applications. Files are identified with the popular extensions like .cnf, .conf or .cfg. These files use formats like INI, JSON, XML, and YAML. We will discuss these in a little detail in this article

Choosing an Appropriate Configuration File Format

The developers can choose a suitable configuration file format that works well with their projects. The complexity of the application depends on what should be configured by the developers. In choosing a file format the developer has to keep in mind that a few file formats are limited to the set of ‘definition utilities’ and others may affect the integrity of the configuration files themselves.


The simplest format for preparing a configuration file is the INI format. This format defines the data in a simple way. Whatever a developer wants to assign to the fields will get associated with it as is shown in the case of PHP. This format is limited in its functionality, it supports groups but does not support higher structures like objects or arrays. For parsing an INI file a simple structure in PHP is used – for example parse_ini_string() or parse_ini_file().


This is the most flexible configuration file format. We say so because of its descriptive nature and the way it can be transported to other structures or formats. This file format is dependent upon the ‘Document Object Model’. The developer needs to understand specific entities and he is required to have pre-requisite knowledge for defining proper documents. This format uses the traditional scripts – that is XSLT. To parse an XML file, developers can use the ‘XML Parser’ extension by default.


This is a versatile format and not a pure configuration file format. It is often counted as an ‘Object Notation’ as it is a data structure. It uses a file extension like “.json”. Its major benefit is that it restricts itself to the same ‘syntax’. This way it restricts the configuration to only the integers, Booleans, strings or the floats. The only con of JSON is that the developer must configure its application with the file format that is mainly used to transport the data from one end-point to the other end-point. The parse of JSON can be done with the help of json_decode().


This file format combines the advantages of XML and JSON into a single but distinct file format.  It acts as the configuration file format to define not only the documents but also the data notations. This file format also supports an array of features that may not be common to the entity linking or the object notations or the file documents.

YAML supports the same ‘syntax’ as JSON does. Here the developer has the support of 3rd party libraries when it comes to parsing the YAML files. The 3rd party libraries available include YAML PHP Extension and Symfony YAML These libraries help with components that are not bundled with the format of the PHP File.


.Properties File Format

The “.properties file format” is mainly used where development is done in java related technologies. This file extension ‘.properties’ specializes in the hash table and is saved as ‘java.util.Properties’. This file format is also used for storage strings that are for localization and Internalization – further known as ‘Property Resource Bundles’. There are several formats used here

  • key = value
  • key=value
  • key  value
  • key: value

Overall, it is seen that XML works best as a configuration file format. This is because of its flexibility and descriptive nature. Therefore, developers can choose this file format for transporting and defining their documents.

In configuration file hell? Take a look at Config, the easiest way to manage your application configuration across all your servers and environments.

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