What is a Changelog?

A changelog is a detailed record of changes made to a project, often including fixes and new features. Each file or document in a project may include its own log of changes, in addition to a master project log. A changelog usually consists of a chronological list detailing changes that have been made and who made them. Changelogs are used by developers in the creation and maintenance of software, hardware, web and documentation projects.

Changelog files are usually organized into paragraphs which describe all of the changes associated with a specific goal. Each paragraph often begins with the change date, author's name and email address. The name of each modified file is listed, along with the function or section which was changed. A brief reason with a few details about the change is frequently provided as well. Changelogs are vital in projects involving many developers over time, such as open-source software.

Software project changes can also be logged automatically with a source code revision control system. These systems usually track changes made to code and project files in order to efficiently rebuild software under development. They keep their own internal changelog files and can generate human-readable records of all files changed. These systems often automatically include specially-marked comments from the code files in their change reports. This allows a useful record of specific source code changes to be maintained.

A documentation project may also include changelog files or simply a list of revisions in the main document. Word processors often include a change tracking mechanism that indicates every change made, down to the last character. In contrast, a document changelog can provide a more general level of revision tracking. Some documentation tools can create and maintain this information automatically. They may prompt the writer for information about changes and include it in a section of the document or keep it in a separate file.

Computer hardware projects can use changelog files to track modifications to schematics, diagrams and simulator files. Logs are also utilized by web designers to track website changes and code alterations. Project management efforts of all sorts can benefit from modification records as well. A changelog is useful in any project where it may be important to understand how previous versions are different from the current one.

Release notes are usually based upon project changelogs, but are often focused on bug fixes and product enhancements. They are frequently written at a more general level and may discuss the impact of the changes on product users. They may also include instructions on how to re-create specific problems and describe tests performed to verify the fixes. In general, release notes address product functionality rather than individual modifications to specific product files.