Kraken.io is a well-regarded image optimization API with a clean REST interface, support for lossless and lossy compression modes, and additional image manipulation features like resize and WebP conversion. ChangeThisFile takes a broader approach: format conversion across 9 file categories, not just images.
For pure image optimization, Kraken.io is genuinely good. This comparison helps you understand where the tools overlap, where they diverge, and why you might reach for one over the other.
Quick verdict
For lossless or lossy image compression with precise control: Kraken.io. It has well-tuned compression algorithms and good documentation for optimization-heavy workflows.
For format conversion (HEIC → JPG, PDF → DOCX, MP4 → WebM): ChangeThisFile. 690 routes, free API tier, call /v1/convert directly with curl or any HTTP client.
For video, audio, documents, or ebooks: ChangeThisFile. Kraken.io is image-only.
For a free API with no card required: ChangeThisFile — 1,000 conversions/month. Kraken.io has a free tier but requires a credit card.
Pricing comparison
Competitor pricing below is as of April 2026 - check the vendor's current pricing page before deciding.
| Plan | ChangeThisFile | Kraken.io |
|---|---|---|
| Free tier | 1,000 conversions/month (no card) | ~100MB/month (card required to activate API) |
| Entry paid | $29/mo — 10,000 conversions | $5/mo — 500MB/month |
| Mid tier | $99/mo — 50,000 conversions | $19/mo — 5GB/month |
| High volume | $499/$1,999/mo | $179/mo — 100GB/month |
| Pricing model | Per conversion (flat count) | Per MB of image data processed |
| Images only? | No — 9 categories | Yes |
Kraken.io bills by data volume (MB of images processed), while ChangeThisFile bills per conversion. For large images processed in low quantities, Kraken's MB-based pricing can be more expensive. For many small images, it can be cheaper. ChangeThisFile's flat per-conversion pricing is more predictable regardless of file size.
Feature comparison
| Feature | ChangeThisFile | Kraken.io |
|---|---|---|
| Free API tier (no card) | Yes — 1,000/mo | No (free tier requires card) |
| SDK required | No — curl/fetch/requests directly | No (REST API, has optional SDKs) |
| Image compression | No (format conversion only) | Yes — lossless + lossy modes |
| Image format conversion | Yes — HEIC, PSD, AVIF, WebP, etc. | Yes — WebP output + format conversion |
| Resize / crop | No | Yes — multiple resize strategies |
| Video conversion | Yes | No |
| Document conversion | Yes | No |
| Client-side conversions | Yes — 161 browser routes | No |
| S3/URL source | No (file upload only) | Yes (URL and S3 sources) |
| Webhooks | Yes (HMAC-signed) | Yes (callback URL) |
| Async processing | Yes (files >100MB) | Yes |
Format coverage
Kraken.io covers JPEG, PNG, GIF, SVG, and WebP with lossless and lossy modes. Image manipulation features include resize, crop, auto-orient, and background fill. It also supports image URLs and S3 buckets as input sources — useful for pipeline integration. Kraken is image-only with no document, video, or audio support.
ChangeThisFile covers 690 conversion 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, FB2. Archives: ZIP, RAR, 7Z, TAR.
For image-only workflows, Kraken has the advantage of S3 and URL input sources. For mixed-format workflows, ChangeThisFile covers significantly more ground.
API and developer experience
Kraken.io API is well-documented REST with support for file upload, URL fetch, and S3 integration. Optional SDKs exist for major languages. The API has a clear distinction between sync and async modes — small files can be processed synchronously; large files or batch jobs use callbacks.
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=@image.png" \
-F "target=webp" \
--output result.webp
Source format auto-detected from filename. Get a free key at changethisfile.com/v1/keys/free — no card required. For files over 100MB, async job mode is automatically used with HMAC webhook callbacks. Idempotency keys (Stripe-style) are supported for safe retry logic.
When to choose which
| Use case | Recommended |
|---|---|
| Lossless/lossy image compression | Kraken.io |
| S3 or URL-based image processing | Kraken.io |
| Convert HEIC, PSD, AVIF, or raw image formats | ChangeThisFile |
| Convert video, audio, documents, or ebooks | ChangeThisFile |
| Free API tier with no card | ChangeThisFile |
| Direct HTTP — curl or requests works without a library | Both |
| Predictable per-conversion pricing | ChangeThisFile |
| Privacy — files never leave browser | ChangeThisFile (client-side routes) |
Kraken.io is a well-built image optimization API — if lossless/lossy compression, S3 integration, or resize capabilities are your primary needs, it's worth evaluating. For format conversion beyond images, or for a free API tier without a card, ChangeThisFile is the better fit — 1,000 free conversions/month, 690 routes, callable with curl or any HTTP client.