WordPress Client-side Media Processing

WordPress 7.1 can resize, compress, rotate, convert, and create image derivatives in the browser before files are finalized on the server. Treat this as a second execution path, not as a transparent optimization: server image-editor hooks may not run, attachment metadata can be generated in stages, and the block editor may receive a Document-Isolation-Policy header.

When to use this skill

• A plugin filters image quality, formats, EXIF rotation, sub-size generation, or attachment metadata.
• Code hooks wp_generate_attachment_metadata, intermediate_image_sizes_advanced, image_editor_output_format, wp_image_editors, or image_make_intermediate_size.
• An editor asset, CDN, analytics script, page builder, or media workflow fails only on WP 7.1.
• Code calls /wp/v2/media, reads attachment REST fields, uploads external images, or replaces attachment files.
• A CSP blocks blob: workers or a cross-origin editor dependency stops loading.

Model both processing paths