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Image · Compression

Compress images. Keep them sharp.

Drop a JPEG, PNG, WebP or HEIC. Tune quality with a real-time SSIM preview. Download a smaller file in seconds — without ever leaving your browser.

  • Files never leave your device — encoding runs locally in WebAssembly.
  • SSIM-aware encoder keeps faces, text and edges crisp.
  • Batch up to 50 images, parallelized across your CPU cores.
Supports →
JPEG PNG WebP AVIF HEIC GIF TIFF
→ All output formats

Trusted by 1.2M people · 4.8M images compressed every month

No uploads, no tracking on your images. There's no server endpoint for image data.

1.2M
Monthly users
−84%
Avg. size cut
0
Files uploaded
What people say

Portfolio sites, client work, production deploys.

★★★★★

I compress assets here before every deploy. No cap, no upload, batch of 50 processed in one go.

MR
Marcus R.
★★★★★

The SSIM slider shows the quality trade-off in real time. My blog images are 3× smaller and nobody can tell on screen.

SL
Sarah L.
★★★★★

40 product photos done in about two minutes. Didn't have to sign up or wait for anything to upload.

AT
Andrea T.
★★★★★

Was skeptical about browser-based compression but the output quality surprised me. SSIM 0.97 and the files are genuinely small.

JK
Julia K.
★★★★★

The compression runs in the tab — nothing gets sent. Works for client photos where I can't use an upload service.

DN
David N.
★★★★★

My journalism team compresses dozens of images daily before publishing. Fast, private, and the HEIC support saves us an extra conversion step.

FC
Frances C.
★★★★★

Switched from TinyPNG when I hit the monthly cap for the third time. Never looked back. This does more, for free, and my files never leave my laptop.

TP
Thomas P.
★★★★★

Used it to compress my entire portfolio before an interview. 80% smaller, still looks perfect on a retina display. Bookmarked immediately.

EV
Helen V.
★★★★★

I compress assets here before every deploy. No cap, no upload, batch of 50 processed in one go.

MR
Marcus R.
★★★★★

The SSIM slider shows the quality trade-off in real time. My blog images are 3× smaller and nobody can tell on screen.

SL
Sarah L.
★★★★★

40 product photos done in about two minutes. Didn't have to sign up or wait for anything to upload.

AT
Andrea T.
★★★★★

Was skeptical about browser-based compression but the output quality surprised me. SSIM 0.97 and the files are genuinely small.

JK
Julia K.
★★★★★

The compression runs in the tab — nothing gets sent. Works for client photos where I can't use an upload service.

DN
David N.
★★★★★

My journalism team compresses dozens of images daily before publishing. Fast, private, and the HEIC support saves us an extra conversion step.

FC
Frances C.
★★★★★

Switched from TinyPNG when I hit the monthly cap for the third time. Never looked back. This does more, for free, and my files never leave my laptop.

TP
Thomas P.
★★★★★

Used it to compress my entire portfolio before an interview. 80% smaller, still looks perfect on a retina display. Bookmarked immediately.

EV
Helen V.
Anatomy · 01

DCT, quantization, and the bytes you never look at.

JPEG splits your image into 8×8 blocks and runs a Discrete Cosine Transform. The high-frequency coefficients — fine grain, micro-noise, sensor speckle — get rounded away first. We tune the quantization tables per-image so smooth regions survive and edges stay crisp.

  • 4:2:0
    Chroma subsampling
    Your eye sees 4× more luminance detail than color. We throw away 75% of the color data — you can't tell.
  • DCT
    Frequency-domain truncation
    Smooth blue sky? 8 bytes. Sharp logo? 600 bytes. The encoder spends bits where they matter.
  • MOZJ
    Trellis-quant mozjpeg
    5–20% smaller files than libjpeg-turbo at identical perceptual quality, compiled to WebAssembly.
Anatomy · 02

SSIM is the only number that actually means "looks the same".

PSNR rewards mathematical fidelity. SSIM rewards perceptual fidelity — luminance, contrast, and local structure, the things your eye actually evaluates. We expose SSIM as the dial because it correlates with what you mean by "good enough".

  • ≥0.97
    Indistinguishable
    Side-by-side test: no human picks the original.
  • 0.92
    Sweet spot for web
    Half the bytes, no one notices on a screen.
  • 0.80
    Aggressive — and visible
    Good for thumbnails, message previews, hero blur backdrops.
How it works

Three steps. Zero uploads.

Drag a file in, tune the dial, take the bytes home. The whole pipeline runs in a Web Worker on your machine.

01 / DROP

Drag the file onto the folder.

JPEG, PNG, WebP, AVIF, HEIC or GIF. Up to 50 at a time. Or pick from your device — Finder, Photos, anywhere.

02 / TUNE

Slide the dial to your SSIM target.

Real-time preview updates as you drag. The encoder picks the smallest file that stays above your perceptual threshold.

SSIM target0.96
≈ −68% file size
03 / KEEP

Download. Or batch-zip the lot.

One click. Stripped EXIF by default (keep it if you want). Single file or ZIP for batches — never an email, never an account.

colosseo.webp
412 KB2752 × 1536 · q78
The honest comparison

kindatool vs. the ones that upload.

Not because they're bad — because they don't have to be your default.

Feature comparison
★ Best pick kindatool
TinyPNG
Adobe Express
ImageOptim
Runs entirely in your browser
Yes
Server
Server
Desktop app
No account, no email, no sign-up
Never
No login · capped use
Required
N/A
SSIM-targeted encoding
Per-image
HEIC input · WebP / AVIF output
All
Partial
Partial
Partial
Batch size limit
Up to 50 / batch
20 (free)
1 at a time (free)
∞ local
Price
Free, forever
Free web · API pay-as-you-go
Free · $9.99/mo
Free (macOS only)
Things people ask

Common questions about compression.

Does kindatool upload my images anywhere?
No. Every byte of compression happens locally in your browser using a WebAssembly build of mozjpeg, libwebp, libavif and libheif. Open DevTools → Network and you'll see zero outbound requests when you compress. We don't have a server to upload to in the first place.
Which formats can I compress?
JPEG, PNG, WebP, AVIF, HEIC, GIF and TIFF on input. JPEG, PNG, WebP and AVIF on output. You can also cross-convert — e.g. drop an iPhone HEIC, get a 90% smaller WebP back.
What is SSIM and why do you expose it as a dial?
SSIM (Structural Similarity Index) measures how perceptually similar two images are — luminance, contrast and local structure rolled into one number from 0 to 1. We target SSIM instead of raw quality=85 because a photo of a beach can hit SSIM 0.97 at quality 70, while a screenshot of a spreadsheet needs quality 92 to look the same. Same dial, smarter outcome.
Is there a file size limit?
Only your device's RAM. On a modern laptop you can comfortably process 100 MP images and batches of up to 50 files at a time. We process images in chunks so very large files won't tab-crash you.
Will compression strip my metadata?
By default we strip EXIF, GPS coordinates and thumbnail metadata for privacy. From the advanced panel you can keep camera orientation, ICC colour profile, or the full EXIF block. The choice stays with you — it's your photo.
How is this different from TinyPNG, Squoosh, or Photoshop "Save for Web"?
TinyPNG uploads your files to their servers and caps you on volume. Squoosh is local but single-file only. Photoshop is local but $20/month and overkill for compression. kindatool is local, batched, free, and tunes the encoder per-image with SSIM — the closest thing to "Save for Web" without the subscription.
Pair it with

More image tools.

Resize
Lanczos & Mitchell filters, locally.
Open →
Convert
HEIC, AVIF, WebP, PNG, JPEG.
Open →
Rotate
90°, 180°, free-angle.
Open →
Watermark
Text or logo, batch overlay.
Open →
Blur
Gaussian, motion, faces.
Open →

Drop your folder. Take back your bytes.

Or paste a URL — we'll fetch it client-side via the browser's image cache and run the same pipeline. Nothing routes through us.

No upload No account No watermark No limits