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Open Opus is a free and open source API to classical music metadata.

It provides composers, works and performers information to classical music apps such as Concertmaster. It's written in PHP and relies on a MySQL database. It's free and everybody can use it directly. Additionally, all Open Opus data is in the public domain and can be freely used.


It's a public RESTful API which returns data in JSON format. There is a doc explaining all endpoints and data structures. No registration needed.

How to build

  1. Fork and clone this git repository to your webserver (for example, in the /var/www/ folder)
  2. The Open Opus API uses a shared Open Opus utilities library. Clone it in the same directory
  3. Create a MySQL database (for example, openopus) and load its strucuture
mysql -u USER -p openopus < /var/www/openopus_api/sql/openopus.sql
  1. Install the Composer vendor packages:
cd /var/www/openopus_api/
composer install
  1. Create an inc.php file from the example:
cd /var/www/openopus_api/lib/
cp inc-example.php inc.php
vim inc.php
  1. Change variable values in the lib/inc.php accordingly to your webserver

MySQL settings

Open Opus search functionality needs special configurations on your MySQL database. Update your server's my.cnf file (paths may vary on different operating systems) to include two extra directives:

innodb_ft_min_token_size = 1
innodb_ft_enable_stopword = 0

Data import

To import the full Open Opus dataset to your fork, simply:

  1. Remove the 2nd line from the html/dyn/composer/importdump/index.phtml file
  2. Open the following URL in your web browser:

Replace the domain above with the one your app will use.

Additionally, you can download the data directly through the API:

Search data

The search database will be renewed automatically every night (see "cache cleaning routines", below). To make the first import, simply run on command line:

php /var/www/openopus_api/cln/omnisearch.php

Google Cloud Storage

The Open Opus API uses Google Cloud to store image files. In order to use it, you must:

  1. Create a keys directory in /var/www/openopus_api/ and put your Google Cloud keyfile.json in it
  2. Change the Google Cloud variables in the lib/inc.php accordingly to your Google account

Composer portraits

There are 220 composer portraits in the portraits directory. If you want to upload them to your cloud:

  1. Remove the 2nd line from the html/dyn/composer/portraitupload/index.phtml file
  2. Open the following URL in your web browser:

Replace the domain above with the one your app will use.

Cache and cache cleaning routines

The Open Opus API can cache its results, saving server resources. In order to activate this feature you must:

  1. Give ownership of the public directory to the web server group (e.g., www-data):
chgrp www-data /var/www/openopus_api/html -R
  1. Set the environment variables for root:
vim /etc/environment
export BASEOPENOPUSDIR="/var/www/openopus_api/html"
  1. Update crontab for root (this will set the cache-cleaning and search-building routines)
# m     h       dom     mon     dow     command
0       2       1       *       *       /var/www/openopus_api/cln/
0       1       *       *       *       php /var/www/openopus_api/cln/omnisearch.php


There is a single public directory in the project (/html) and it must have its own virtual host on your webserver. (For example, we host it at

The API must be served with HTTPS. You can use a free Let's Encrypt-provided certificate, it's perfectly fine.

CORS Settings

Open Opus is a publicly available API, so its CORS settings are fully permissive (Access-Control-Allow-Origin: *).

If you plan your fork to be more restrictive, you can make it accept requests only from trusted domains. Just remove the first line of the html/.htaccess file and implement the following configuration in your webserver (it must be placed inside the <virtualhost> directive):

SetEnvIf Origin ^(https?://(?:.+\.)?(example\.com|expl\.me)(?::\d{1,5})?)$   CORS_ALLOW_ORIGIN=$1
Header append Access-Control-Allow-Origin  %{CORS_ALLOW_ORIGIN}e   env=CORS_ALLOW_ORIGIN
Header merge  Vary "Origin"

Change the domains above to the ones your app will use.

Contributing with code

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Contributing with data

Open Opus is a free, wiki-style, open source database. You can review existing info or add new entries to the database - any help will be appreciated!

Contributing with money

Open Opus is free to use but it runs on web servers that cost us money. You can help us by supporting us on Patreon - any amount is more than welcome!


API: GPL v3.0 Data: Public Domain


A free and open source API to classical music metadata







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