API Documentation

Convert files between 500+ format pairs with a simple REST API. Video, audio, documents, images, ebooks, archives, and more.

Quick Start

Get converting in two steps. No credit card required.

1 Get a free API key

curl -X POST https://changethisfile.com/v1/keys/free \
  -H "Content-Type: application/json" \
  -d '{"email": "you@example.com"}'Copy

Response:

{
  "api_key": "ctf_sk_abc123...",
  "plan": "free",
  "monthly_limit": 100
}

2 Convert a file

curl -X POST https://changethisfile.com/v1/convert \
  -H "Authorization: Bearer ctf_sk_abc123..." \
  -F "file=@document.docx" \
  -F "target=pdf" \
  -o document.pdfCopy

That's it. The converted file is returned as a binary download.

Anonymous API

Convert a file without authentication. Rate-limited by IP address. Good for quick testing.

Example

curl -X POST https://changethisfile.com/api/convert \
  -F "file=@input.docx" \
  -F "source=docx" \
  -F "target=pdf" \
  -o output.pdfCopy

Authenticated API

Convert a file with an API key. Higher rate limits, larger files, and monthly quota tracking.

Send your API key in the Authorization header:

Authorization: Bearer ctf_sk_your_api_key

Example

curl -X POST https://changethisfile.com/v1/convert \
  -H "Authorization: Bearer ctf_sk_your_key" \
  -F "file=@video.mkv" \
  -F "target=mp4" \
  -o video.mp4Copy

Response

On success, returns the converted file as a binary download with these headers:

Check Usage

curl https://changethisfile.com/v1/usage \
  -H "Authorization: Bearer ctf_sk_your_key"Copy

{
  "plan": "free",
  "conversions_this_month": 42,
  "monthly_limit": 100,
  "max_file_size": 100000000,
  "rate_per_minute": 10
}

Tool API

Run file operations like merge, split, and compress. Accepts one or more files and returns the processed result.

Example: Merge PDFs

curl -X POST https://changethisfile.com/api/tool \
  -F "files=@page1.pdf" \
  -F "files=@page2.pdf" \
  -F "files=@page3.pdf" \
  -F "category=pdf" \
  -F "action=merge" \
  -o merged.pdfCopy

Batch API

Convert multiple files in a single request. Returns a ZIP archive containing all converted files.

Example: Convert multiple images

curl -X POST https://changethisfile.com/api/batch-convert \
  -F "files=@photo1.png" \
  -F "files=@photo2.png" \
  -F "files=@photo3.png" \
  -F "target=jpg" \
  -o converted.zipCopy

Formats

Returns all supported conversion routes. No authentication required.

curl https://changethisfile.com/v1/formatsCopy

{
  "formats": {
    "png": [
      { "target": "jpg", "engine": "canvas", "tier": "free" },
      { "target": "webp", "engine": "canvas", "tier": "free" }
    ],
    "docx": [
      { "target": "pdf", "engine": "libreoffice", "tier": "free" }
    ]
  },
  "total_routes": 500
}

Supported categories include images, video, audio, documents, spreadsheets, ebooks, archives, data formats, and fonts.

Error Codes

All errors return JSON with an error field describing what went wrong.

{
  "error": "Unsupported conversion: bmp to mp4"
}

Rate limit response

{
  "error": "Rate limit exceeded. Max 5 conversions per minute.",
  "retry_after": 60
}

Quota exceeded response

{
  "error": "Monthly quota exceeded",
  "limit": 100,
  "used": 100,
  "plan": "free",
  "upgrade_url": "https://changethisfile.com/dashboard#upgrade"
}

Rate Limits & Plans

Anonymous (no API key)

Authenticated (API key)

Need more conversions? Buy credit packs for pay-as-you-go usage beyond your plan limits.

OpenAPI Spec

A machine-readable OpenAPI 3.0 specification is available at:

https://changethisfile.com/v1/openapi.yamlCopy

Use it with tools like Postman, Swagger UI, or any OpenAPI-compatible client to explore and test the API.