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Diagnostics
This is the screen the plugin is built around. Everything on it comes from measurements taken on your server, not from assumptions.
A single 0–100 figure, weighted towards the things that matter most: WebP support (35), AVIF support (35), a lossless JPEG tool (10), a writable uploads directory (10), and correct AVIF delivery conditions (10).
| Score | Reading |
|---|---|
| 80–100 | Everything needed is present |
| 50–79 | Usable, but something is missing — the reasons say what to ask for |
| 0–49 | Most of what is required is absent |
Formats down the side, libraries across the top.
| Cell | Meaning |
|---|---|
| ✓ verified | A real encode succeeded and the output passed every check. Hover for the bytes and milliseconds. |
| **~ claimed** | The library says it supports this but the test failed. The format stays off. Hover for why. |
| ✗ | Not offered. |
The middle state is the important one. A library can report a format it cannot actually write — this is common with Imagick builds whose delegate is broken. Trusting that report is how sites end up with corrupted images discovered weeks later. The plugin encodes a known 64×64 sample, checks the magic bytes, confirms the size is plausible, and reads the result back before believing anything.
When more than one engine can produce a format, they are measured against the same 512×384 test photograph and the smallest output wins, with speed as the tie-breaker.
This uses a different, larger sample than the verification test on purpose. On a
64×64 image the differences between engines vanish — cwebp -m 6 even comes out
two bytes larger than -m 4. On a photograph it is 7% smaller. Ranking on the
small sample would pick the wrong engine.
There is no built-in preference for one library over another. Whichever produces the smallest file on your server wins.
Every recommendation carries its reason. Items are marked:
- ✓ good — a decision made, with the measurement behind it
- ! warning — works, but something would improve it
- ✗ error — a blocker, listed under To resolve
Click Apply the recommended configuration to write them all at once. The values still pass through the same validation as manual edits.
Raw facts: PHP version, memory limit, execution time, whether commands can be
run, open_basedir, whether uploads are writable, whether PHP file uploads are
enabled, whether .htaccess is writable, and the MIME type your server actually
returns for .avif files.
That last row is worth checking. If it says the server does not know
image/avif, see Delivering images.