Determine the stored bitstream family without guessing from file size, transparency, or appearance. The detector inspects VP8 and VP8L payload identifiers, including the image data nested inside animation-frame chunks, and labels mixed-frame animations honestly.
How to use Lossy/Lossless Detector
- Add WebP files whose actual compression mode you need to identify.
- Run the local detector to inspect still payload chunks and every readable animated-frame payload.
- Review lossy, lossless, mixed, or unknown status and copy the JSON explanation when documenting an asset pipeline.
What this tool is good at
When to use Lossy/Lossless Detector
Make a precise encoding decision
Verify whether a still payload uses VP8, VP8L, or whether animation frames mix both bitstream families. The result is based on the selected file's actual bytes or decoded frames, so it can support a concrete publishing or engineering decision instead of a filename-based assumption.
Troubleshoot a private production asset
Use the browser-local workflow for client images, unreleased campaigns, product media, or internal fixtures when sending the source to a generic third-party utility would create unnecessary exposure.
Document repeatable asset checks
Keep the generated output or JSON report with a ticket, content review, or migration record. Use the current payload classification for delivery diagnostics, not as a claim about the image's entire editing or source history. This makes the finding reproducible for another editor or developer.
How to choose the right settings
Start from the intended destination
Use the current payload classification for delivery diagnostics, not as a claim about the image's entire editing or source history. Choose settings or interpret results in the context of the actual CMS, browser, editor, size budget, animation player, or privacy policy that will consume the WebP.
Separate container facts from visual judgment
RIFF chunks, dimensions, alpha values, and encoded bytes answer technical questions, while perceived sharpness, acceptable motion, and brand appearance still require a human preview at the real display size.
Retain the authoritative original
A VP8L result cannot restore detail lost before WebP creation, and no reliable original lossy quality number is recoverable. Keep the source until the derivative or report has been reviewed, downloaded, and tested in the destination workflow.
Practical workflow and output details
Top-level image chunks and image data nested inside every ANMF frame are inspected directly instead of inferring encoding from size or alpha. File bytes remain in the current browser tab; only static application code or codec assets are fetched, and no image-processing request is sent to PicConverters.
A VP8L result cannot restore detail lost before WebP creation, and no reliable original lossy quality number is recoverable. The tool reports or changes only the scope named on the page and avoids implying broader repair, anonymity, visual quality, or cross-application compatibility than the operation can establish.
Format behavior and limitations
Lossless identifies VP8L storage, not proof that the pixels were never previously transformed by a lossy format or editing workflow.
A high-quality VP8 file remains lossy, while a VP8L file may still contain artwork that originated from JPEG; this tool describes the current WebP payload only.
Frequently asked questions
Can WebP animation contain mixed encoding?
Yes. Individual ANMF frames can carry VP8 lossy or VP8L lossless image data, so an animation may be reported as mixed.
Does transparency mean lossless?
No. Lossy VP8 can use a separate ALPH chunk, while VP8L can also store alpha. Transparency alone does not identify encoding.
Can this recover a quality number?
No. It identifies the bitstream family, not the encoder's original quality setting.
Related WebP tools
WebP File Analyzer
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WebP Quality Changer
Re-encode static WebP images at a deliberate quality level and compare genuine output size before downloading.
WebP Validator
Validate RIFF bounds, image payloads, animation structure, dimensions, and feature-flag consistency without altering the file.