How We Compared These Tools
We tested each tool with a representative set of images: a 6 MB portrait JPEG from a modern smartphone, a 4 MB landscape photo, a 1 MB PNG screenshot with text, and a 2 MB PNG graphic with transparency. We measured output file size at default settings, visual quality (checking for artefacts, blurring, colour shifts), privacy model (upload vs local), and format support. We also checked practical constraints: batch limits, file size caps, offline capability, and API availability.
TinyPNG / TinyJPG
TinyPNG is the most popular free web-based image compressor, with over 1 billion images optimised. It uses smart lossy compression for PNGs — specifically, it reduces the colour palette using quantisation, producing files 50–70% smaller than standard lossless PNG at near-identical visual quality. For JPEGs it uses MozJPEG. The free tier allows 20 images per month at up to 5 MB each. The Pro plan removes the monthly limit and raises the file size cap to 75 MB. Pros: best-in-class PNG compression; simple drag-and-drop; API for developers; Photoshop and WordPress plugins; trusted by Airbnb, Microsoft, Samsung. Cons: images are uploaded to Tinify's servers — not suitable for sensitive content; no manual quality slider; AVIF only on Pro plan. Best for: developers and WordPress users who compress lots of PNGs and don't have privacy constraints.
Squoosh (by Google)
Squoosh is Google Chrome Labs' open-source browser-based compressor. It runs entirely in the browser using WebAssembly — nothing is ever uploaded. Squoosh supports the widest format range of any free tool: MozJPEG, OxiPNG, WebP, AVIF, JPEG XL, and more. Its standout feature is the side-by-side quality comparison: you see original vs compressed in real time as you adjust settings, with pixel-accurate diff view. This makes it exceptional for precision work. Pros: no upload, fully private; all modern formats including AVIF and JPEG XL; side-by-side quality preview; open source; no limits. Cons: one image at a time only; AVIF encoding is slow; no batch processing; no PDF tools; heavier page load than simpler tools. Best for: developers and designers who need maximum format control and privacy on individual images.
MiniFiles
MiniFiles is built specifically for users who need compression to be private by design — and who work with more than just images. It compresses JPEG, PNG, WebP, and GIF images entirely in the browser, plus it compresses PDFs using Ghostscript compiled to WebAssembly, and offers PDF password protection. Nothing is ever uploaded. MiniFiles is the only client-side tool in this comparison that handles PDFs as well as images. Pros: no upload ever; covers images and PDFs in one place; batch image processing; PDF password protection; simple interface for non-technical users; unlimited usage with a free account (10 files per day as a guest) and no file size limits from server constraints; GDPR-safe by design. Cons: no AVIF or JPEG XL output; output format conversion and custom resizing require Pro. Best for: business professionals, legal teams, healthcare workers, and anyone who needs to compress both images and PDFs privately without installing software.
Compressor.io
Compressor.io is a cloud-based tool supporting JPEG, PNG, WebP, SVG, and GIF with both lossy and lossless modes. The interface is clean and the compression quality is good. However, the free tier is extremely limited: only 1 image per day. A paid plan is required for regular use. Images are uploaded to Compressor.io's servers. Pros: SVG and GIF compression (which most other tools lack); lossy and lossless mode; clean interface; good results. Cons: 1 image/day free limit makes it impractical for most use cases; cloud upload; no AVIF; paid plan required for real volume. Best for: occasional SVG or GIF compression specifically — it supports these formats where most browser-based tools don't.
ImageOptim (Mac Only)
ImageOptim is a free Mac desktop application that provides unlimited batch compression using multiple bundled algorithms: MozJPEG, pngquant, SVGO, and others. It automatically strips EXIF metadata. Because it's a local desktop app, nothing is uploaded anywhere. Pros: unlimited batch processing; multiple algorithms; strips EXIF; free; no internet required. Cons: Mac only — no Windows or Linux version; desktop app requires installation; no WebP or AVIF output; no PDF support. Best for: Mac users — web developers, photographers, bloggers — who need to compress large batches of images without size limits. The best free batch option on Mac.
ShortPixel
ShortPixel is a cloud-based tool with a web interface, API, and WordPress plugin. Its compression algorithm is excellent — proprietary and consistently one of the best across formats. It supports JPEG, PNG, GIF, WebP, AVIF, and PDF. The WordPress plugin automatically compresses images on upload and generates WebP/AVIF alternatives. Free tier: 50 credits/month. Pros: excellent algorithm; AVIF and WebP output; best-in-class WordPress plugin; CDN option; PDF compression. Cons: cloud upload — images sent to ShortPixel servers; only 50 free credits/month; account required for API. Best for: WordPress site owners who want automatic image optimisation. The plugin is among the most popular in the WordPress ecosystem.
Side-by-Side Comparison Table
TinyPNG: privacy = uploads to server, free limit = 20/month, formats = JPEG/PNG/WebP/AVIF (AVIF Pro only), batch = yes (20), AVIF = Pro only, PDF = no. Squoosh: privacy = fully local, free limit = unlimited, formats = JPEG/PNG/WebP/AVIF/JPEG XL, batch = no (1 at a time), AVIF = yes, PDF = no. MiniFiles: privacy = fully local, free limit = 10/day as a guest, unlimited with a free account, formats = JPEG/PNG/WebP/GIF + PDF, batch = yes, AVIF = no, PDF = yes. Compressor.io: privacy = uploads to server, free limit = 1/day, formats = JPEG/PNG/WebP/SVG/GIF, batch = no, AVIF = no, PDF = no. ImageOptim: privacy = fully local, free limit = unlimited, formats = JPEG/PNG/GIF, batch = yes, AVIF = no, PDF = no. ShortPixel: privacy = uploads to server, free limit = 50/month, formats = JPEG/PNG/GIF/WebP/AVIF/PDF, batch = yes, AVIF = yes, PDF = yes.
Which Tool Should You Use?
For sensitive images (client work, medical, legal, personal): MiniFiles or Squoosh — nothing is uploaded. For best PNG compression quality: TinyPNG — its lossy quantisation is unmatched. For maximum format control (AVIF, JPEG XL): Squoosh — most codecs of any free tool. For images and PDFs together, privately: MiniFiles — the only client-side tool covering both. For Mac batch processing: ImageOptim — unlimited, free, no install beyond the app. For WordPress automatic optimisation: ShortPixel — best plugin in the ecosystem. For SVG or animated GIF compression: Compressor.io — supports these where most browser tools don't. For simplest possible experience: TinyPNG for PNGs, MiniFiles for anything private.
The PNG Compression Caveat
Squoosh in OxiPNG mode uses standard lossless PNG compression. TinyPNG uses a lossy quantisation approach — it reduces the colour palette — which produces files 50–70% smaller with near-identical visual quality. MiniFiles also quantises PNGs locally, to a palette of up to 256 colours set by its quality slider. If PNG file size is critical, a quantising tool will beat a lossless one. For JPEGs, WebP, and AVIF, the difference between tools using the same underlying codecs (MozJPEG, libwebp, libavif) is much smaller. The choice between tools for JPEG is mainly about privacy model and workflow, not compression quality.