ConvertAPI has been serving developers since 2013 with a REST API focused heavily on PDF generation and document conversion. It's used in production by many teams and has client libraries in a dozen languages. ChangeThisFile takes a different philosophy: a single standard HTTP endpoint, no proprietary client libraries. One POST with a file and a target parameter. That's it.
This comparison covers pricing, format coverage, privacy, and the specific API design decisions that might make one or the other a better fit for your stack.
Quick verdict
For individuals and side projects: ChangeThisFile. 1,000 free API calls/month with no card gets you to production before you spend a dollar.
For PDF-heavy workflows: ConvertAPI has deep support for PDF manipulation — splitting, merging, form-filling, watermarking. If that's your primary use case, evaluate both carefully.
For developer experience with minimal dependencies: ChangeThisFile wins. Call /v1/convert directly with curl or any HTTP client — no client library to version-pin, no breaking change upgrades. Your existing HTTP client is the only dependency.
For privacy-sensitive files: ChangeThisFile has 161 client-side routes where files never leave the browser. ConvertAPI is entirely server-side.
Pricing comparison
| Plan | ChangeThisFile | ConvertAPI |
|---|---|---|
| Free tier | 1,000 conversions/month (no card) | No free API tier — trial credits only |
| Entry paid | $29/mo — 10,000 conversions | Starts around $9.99/mo for limited use (per their site at time of writing) |
| Mid tier | $99/mo — 50,000 conversions | Multiple plans available; check convertapi.com for current pricing |
| High volume | $499 Scale / $1,999 Growth | Enterprise plans available |
| Browser tool | Free, no signup, unlimited | Web UI available with free trial |
ConvertAPI's pricing model varies by conversion type — some formats cost more credits than others. ChangeThisFile charges one conversion unit per API call regardless of format, which makes cost predictable across all 690 routes.
Feature comparison
| Feature | ChangeThisFile | ConvertAPI |
|---|---|---|
| Free API tier | Yes — 1,000/mo, no card | No — trial credits only |
| SDK required | No — POST to /v1/convert with any HTTP client | Client libraries available (optional) |
| Client-side conversions | Yes — 161 browser routes, zero upload | No — all server-side |
| Conversion routes | 690 | Wide format support, PDF-strong |
| API authentication | Bearer token, single key | API secret token |
| Webhooks | HMAC-signed, ~25 lines stdlib to verify | Supported on higher plans |
| Async / job queuing | Yes (above 100MB inline threshold) | Yes |
| PDF manipulation (split, merge) | No | Yes — a core strength |
| Idempotency keys | Yes (Stripe-style) | Varies |
Format and route coverage
ConvertAPI's strength is PDF — generation from HTML, Word, Excel, PowerPoint, and images; plus manipulation operations like merge, split, protect, and watermark. If PDF is the center of your workflow, their feature set is deep.
ChangeThisFile covers 690 source→target route pairs across 82 format definitions: images (JPG, PNG, WebP, HEIC, SVG, AVIF, GIF, BMP, ICO, TIFF, PSD), documents (PDF, DOCX, ODT, RTF, HTML, Markdown), spreadsheets (XLSX, CSV, JSON, TSV), video (MP4, MKV, WebM, AVI, MOV, GIF), audio (MP3, WAV, FLAC, AAC, M4A), ebooks (EPUB, MOBI, AZW3), archives (ZIP, RAR, 7Z, TAR variants), and fonts (TTF, OTF, WOFF, WOFF2).
The breadth across categories is ChangeThisFile's advantage; the depth in PDF operations is ConvertAPI's advantage.
Privacy and data handling
ChangeThisFile client-side routes cover all major image formats, CSV/JSON/YAML/TSV/XML/TOML, DOCX→HTML, HTML↔Markdown, fonts, XLSX, and more. These run entirely in the browser — nothing is uploaded, no server processes your data, and the architecture makes this a guarantee rather than a policy.
ChangeThisFile server-side routes upload files over HTTPS, convert them, return the result, and automatically delete the file. There is a 24-hour R2 retention window for async jobs, then deletion.
ConvertAPI processes all conversions server-side. They maintain a privacy policy and do not claim long-term retention, but all files traverse their infrastructure regardless of format or size.
For documents containing PII, financial data, or other sensitive content, client-side processing is a structural advantage that no server-side policy can match.
Developer experience: no SDK required
ConvertAPI ships client libraries for Python, PHP, .NET, Java, Ruby, Node.js, and others. These are convenient but represent a dependency: version pins, security audits, upgrade cycles, and potential breaking changes when the API evolves.
ChangeThisFile took a different approach: the endpoint is a single REST endpoint. One POST to /v1/convert with your file and a target parameter. Source format is auto-detected from the filename. You already have curl, requests, or fetch — that's all you need.
curl -X POST https://changethisfile.com/v1/convert \
-H "Authorization: Bearer ctf_sk_your_key" \
-F "file=@report.docx" \
-F "target=pdf" \
--output report.pdf
There's nothing to install. No pip install convertapi, no npm install @convertapi/client, no gemfile entry. The API speaks standard multipart/form-data over HTTPS. Webhook verification is ~25 lines of HMAC with Python's stdlib or Node's built-in crypto.
Get a free API key at changethisfile.com/v1/keys/free — no card required.
When to choose which
| Use case | Recommended |
|---|---|
| Free API tier for hobby or side projects | ChangeThisFile |
| Zero-dependency HTTP integration | ChangeThisFile |
| Privacy-sensitive files (images, data, docs) | ChangeThisFile (client-side routes) |
| Broad format coverage (video, audio, ebook, archive) | ChangeThisFile |
| PDF manipulation (merge, split, watermark, protect) | ConvertAPI |
| Team already using ConvertAPI client library | ConvertAPI (migration cost not worth it) |
| HTML → PDF pipeline at scale | Evaluate both — ConvertAPI has depth here |
If you're evaluating ConvertAPI for a standard conversion workflow — documents to PDF, images across formats, audio or video transcode — ChangeThisFile's free tier is worth trying first. 1,000 API calls/month, no card, no client library version pinning to manage. For teams that need deep PDF manipulation (splitting, merging, form-filling), ConvertAPI's specialized feature set may justify the cost and the client library dependency.