Composer could not find a composer.json file

Symptoms

When attempting to use composer you get the following error:

Composer could not find a composer.json file

Description 

This happens when you are working within a directory that does not contain a composer.json file.

The most common cause for this error is when you are attempting to use composer in the wrong directory.

The other two most common causes for this would be that you either have not yet installed your application or if you are building a new application from scratch, you have not yet manually created your composer.json file. 

Resolution

1. If you are installing an application or framework, be sure to review the installation instructions to see if there are any specific notes about which directory should be used.

If there are no specific instructions regarding the particular directory to use, you may typically install your application to the document root of your domain. The following guide explains how to find the document root of your domain:

How to find the document root of a domain 

2. You should most often use the installation instructions for your application to install the composer.json file and other application files.

If you are creating your own application from scratch, you can use the official Composer documentation to learn how to create a new composer.json file:

Composer Documentation - composer.json