CPAN Testers Has a New API


As part of the MetaCPAN hackathon, meta::hack, I was invited to work on the CPAN Testers integration. CPAN Testers is a community of CPAN users who send in test reports for CPAN modules as they are uploaded. MetaCPAN adds a summary of those test reports to every CPAN distribution to help you determine which module you'd most like to use. For quite a few months, this integration was broken, and the nature of the current integration (a SQLite database) means it is not as generally useful as it could be.

So, I decided that the best way to improve the CPAN Testers / MetaCPAN integration was to build a new CPAN Testers API. This API uses the CPAN Testers schema to expose CPAN Testers data using a JSON API. This API is built using the Mojolicious web framework, and an OpenAPI specification (using Mojolicious::Plugin::OpenAPI.

Documenting the API using the OpenAPI language automatically generates the application routes, and makes input and output validation very simple (all handled by Mojolicious::Plugin::OpenAPI). Having the API specification be a simple JSON document also makes it possible to automatically generate documentation and display it using Swagger-UI. The Swagger-UI tool even allows users to try out the API right in the browser, displays the input parameters and their documentation, and gives you real output based on the request you input.

Right now, the CPAN Testers API has access to only some of the data CPAN Testers has:

These APIs can be easily used by any HTTP client, and since they return JSON, can be easily manipulated with simple tools like jq or ETL::Yertl:

# Get all test data for every release of the CPAN-Testers-API distribution
curl ''

# Get all Statocles release test data updated since the beginning of 2016
curl ''

# Select all of my releases where there was a failure report
curl | jq '.[] | select( .fail > 1 )'

# Build my own database for personal use!
sqlite3 data.db 'CREATE TABLE release ( dist VARCHAR, version VARCHAR, pass INTEGER, fail INTEGER, na INTEGER, unknown INTEGER )'
curl | yfrom json | yq '.[]' | ysql --dsn dbi:SQLite:data.db --insert release
# ... and then find failed dists
ysql --dsn dbi:SQLite:data.db --select release --where 'fail > 100'

In addition to these standard JSON API calls, the new CPAN Testers API also provides a WebSocket API for getting push notifications of important CPAN Testers events. With just a WebSocket and a JSON parser, you can subscribe to a WebSocket feed of new uploads to CPAN. In the future, all internal CPAN Testers communication will be done through the API using the Mercury message broker on the backend, allowing you to use simple WebSockets to build your own data alerts and updates.

Any WebSocket client can connect to get updates, like so:

# from
$ perl
Got upload: Mercury (0.011) by PREACTION

Once the message is send on the websocket, the archive is available on CPAN Testers CPAN mirror (, so you could immediately start testing it and sending in reports (hint hint)!

This is just the start of what this API could be made to do. If you'd like to use some CPAN Testers data, but it is not yet available from the API, check our contributing guide for how to add new features, and if you have questions here's how to get in contact.

If you'd like to help, but don't know how, here's some possible features that could be implemented to make the API easier to use:

  • You can make the post-filters I use jq and ETL::Yertl for into API query parameters so that I can directly request only the releases with more than 10 failure reports
  • You could make a special filter to only include the latest version of the dist
  • You could add more endpoints to filter the data:
    • /release/dist/{dist}/{version} and /upload/dist/{dist}/{version} to only get a single version
    • /release/dist/{dist}/latest and /upload/dist/{dist}/latest to get the latest version

As always thanks to all the sponsors of CPAN Testers, and specifically to the sponsors of meta::hack for providing the means to get this API started.