ShortPixel specializes in image optimization: it compresses images using lossy, glossy, and lossless algorithms, converts to WebP and AVIF, and integrates directly with WordPress via a popular plugin. The compression quality is genuinely good — comparable to TinyPNG and Kraken.io, with the added AVIF support being a differentiator.
ChangeThisFile doesn't compress — it converts. Different formats, different tools. This comparison covers where they overlap (image format conversion) and where they don't (everything beyond images).
Quick verdict
For compressing images with lossy/glossy/lossless control and WebP/AVIF output: ShortPixel is excellent, especially if you're on WordPress.
For converting files between formats (HEIC → JPG, PDF → DOCX, MP4 → WebM): ChangeThisFile. 690 routes, free API, call /v1/convert directly with any HTTP client.
For video, audio, documents, or ebooks: ChangeThisFile. ShortPixel is image-only.
For a free API with no card required: ChangeThisFile — 1,000 conversions/month. ShortPixel API has a limited free tier.
Pricing comparison
| Plan | ChangeThisFile | ShortPixel |
|---|---|---|
| Free tier | 1,000 conversions/month (no card) | 100 images/month API free tier |
| Entry paid | $29/mo — 10,000 conversions | $4.99/mo — 5,000 images/month |
| Mid tier | $99/mo — 50,000 conversions | $9.99/mo — 12,000 images/month |
| High volume | $499/$1,999/mo | $29.99/mo — 55,000 images/month |
| Pricing model | Per conversion (flat count) | Per image (monthly quota) |
| One-time credits | No | Yes — one-time credit packs available |
ShortPixel also sells one-time credit packs (not subscriptions) — useful for bulk batch jobs without a recurring commitment. ChangeThisFile is subscription-only. Both bill per operation: ShortPixel per image, ChangeThisFile per conversion (same concept, different name).
Feature comparison
| Feature | ChangeThisFile | ShortPixel |
|---|---|---|
| Free API tier (no card) | Yes — 1,000/mo | Yes — 100 images/mo |
| SDK required | No — curl/fetch/requests directly | No (REST API, has PHP/JS libraries) |
| Image compression | No (format conversion only) | Yes — lossy, glossy, lossless |
| WebP conversion | Yes (as format conversion) | Yes (as compression output) |
| AVIF conversion | Yes (as format conversion) | Yes (as compression output) |
| HEIC conversion | Yes | No |
| Resize | No | Yes |
| WordPress plugin | No | Yes |
| Video conversion | Yes | No |
| Document conversion | Yes | No |
| Client-side processing | Yes — 161 browser routes | No |
| Webhooks | Yes (HMAC-signed) | Yes (callback URL) |
Format coverage
ShortPixel covers JPEG, PNG, GIF, PDF (as images), and WebP. It outputs WebP and AVIF for all supported formats. Its three compression modes — lossy (aggressive), glossy (balanced), and lossless (safe) — give developers precise control over quality/size tradeoffs. The WordPress plugin handles bulk optimization of existing media libraries automatically.
ChangeThisFile converts between formats, covering 690 routes across 9 categories. Image: JPG, PNG, WebP, HEIC, AVIF, GIF, BMP, ICO, SVG, TIFF, PSD. Video: MP4, WebM, MKV, AVI, MOV, 3GP, FLV, WMV. Audio: MP3, WAV, FLAC, AAC, M4A, OGG. Documents: PDF, DOCX, ODT, RTF, HTML, Markdown. Data: CSV, JSON, YAML, XML, TOML. Spreadsheets: XLSX, XLS. Fonts: TTF, OTF, WOFF, WOFF2. Ebooks: EPUB, MOBI, AZW3. Archives: ZIP, RAR, 7Z, TAR.
For AVIF and WebP conversion specifically, both tools deliver them — ShortPixel with compression optimization, ChangeThisFile with format conversion. If you want smaller AVIF/WebP files (not just format-changed), ShortPixel's compression pass after conversion can help.
API and developer experience
ShortPixel API is REST-based with optional PHP and JavaScript libraries. You can submit images via URL, file upload, or base64. The API supports batch processing and callback URLs for async results. Well-documented for both one-off and pipeline use.
ChangeThisFile API requires no SDK. The endpoint is the SDK:
curl -X POST https://changethisfile.com/v1/convert \
-H "Authorization: Bearer ctf_sk_your_key" \
-F "file=@photo.heic" \
-F "target=avif" \
--output result.avif
Source format auto-detected from filename. Get a free key at changethisfile.com/v1/keys/free — no card. Supports Stripe-style idempotency keys and HMAC webhooks for large async jobs. Sync response for normal files.
When to choose which
| Use case | Recommended |
|---|---|
| Compress images with lossless/lossy control | ShortPixel |
| WordPress media library optimization | ShortPixel |
| One-time bulk image optimization credit pack | ShortPixel |
| Convert HEIC, PSD, or TIFF to modern formats | ChangeThisFile |
| Convert video, audio, documents, or ebooks | ChangeThisFile |
| Free API tier with no card | ChangeThisFile (1,000/mo vs 100/mo) |
| Zero library dependencies — curl or fetch works directly | ChangeThisFile |
| Privacy — files never leave browser | ChangeThisFile (client-side routes) |
ShortPixel is a strong image optimizer — particularly for WordPress users and developers who need fine-grained compression control including AVIF output. For format conversion, non-image files, or a higher-volume free tier, ChangeThisFile's free API is the better fit — 1,000 conversions/month, no card, 690 routes including video, audio, documents, and ebooks, callable with curl or any HTTP client.