What is the difference between the composer.json and composer.lock files in dependency management?

In managing PHP project dependencies with Composer, there are two key files:

• composer.json — describes the project's dependencies, their versions (often with ranges), and other metadata (authors, scripts, autoloading, etc.). This file is edited by the developer.

• composer.lock — records the exact versions of all installed dependencies (including transitive ones) that were resolved during the last run of composer install or composer update. This file ensures that the same versions are installed on other machines or in CI.

In other words, composer.json sets the requirements, and composer.lock fixes specific versions for reproducibility of the environment.