Certifi

Certifi is a Python package that provides a curated, up-to-date bundle of Mozilla's root certificates to verify the authenticity of SSL/TLS certificates when establishing HTTPS connections from Python applications. The bundle, stored as cacert.pem within the package, replaces or supplements system CA stores to ensure a stable and consistent set of trusted roots across platforms.

Certifi also exposes a function certifi.where() that returns the filesystem path to the bundled CA bundle, enabling libraries to locate and use it programmatically.

Because the Mozilla root store changes over time, certifi is updated regularly. Users update by upgrading the certifi package via pip; libraries that rely on certifi will pick up the updated bundle when they import certifi. In practice, requests and urllib3 commonly rely on certifi for TLS verification.

Usage notes: If an application needs to override, environment variables such as REQUESTS_CA_BUNDLE or SSL_CERT_FILE can point to a different CA bundle.

Impact and scope: Certifi is widely adopted in the Python ecosystem as a standard source of trusted root certificates, reducing reliance on the host OS's CA store in diverse environments. It is maintained by an open-source community and is available on PyPI and GitHub.

Limitations: It reflects Mozilla's root store, which may not include some platform-specific roots; for enterprise air-gapped environments, organizations may need to manage their own CA bundle.