Convertio and Epublys for EPUB Work

Convertio and Epublys overlap on EPUB and PDF conversion, but their toolsets and limits differ. This comparison is written by Epublys. The useful choice is whether you need a general file converter or EPUB-specific editing, validation and chapter tools.

When to keep using Convertio

Convertio handles many document, image, audio, video and archive formats. Its current plans use conversion credits and have their own file-size and concurrency limits. Check those limits against your files before choosing a plan. If you need OCR for scanned pages or formats outside Epublys' supported inputs, a general converter may be the better fit.

What Epublys adds for EPUB work

• EPUB operations beyond conversion: merge books, extract chapters, edit metadata and covers, and run structural validation with limited auto-fix.
• Published free limits: 3 tool operations per day on the website, 5MB per file by default, 10MB for PDF to EPUB and 15MB for split, with 20MB total per operation. Reading and previewing do not spend an operation.
• Pro: $9/month or $72/year, no daily operation cap, 30MB total per operation and no Epublys output branding. AI covers are a Pro feature.
• No persistent file storage: tools process uploads in memory and return the result. Your files still travel to the server over HTTPS; the web reader keeps the book file on your device.

Compare the output before switching

Try the same representative book in both converters. Check chapter order, headings, pictures, punctuation and the output in your destination reader. Epublys' EPUB-to-PDF output is a new page layout using bundled fonts; it does not preserve every source CSS rule. PDF-to-EPUB extracts existing text and has no OCR, so a scanned PDF needs OCR elsewhere first.

Start with EPUB to PDF or PDF to EPUB, then use the structural validator to check an EPUB result. For publication, also run EPUBCheck and preview the file.

API and agent access

Epublys exposes its EPUB tools through REST and MCP with the same Bearer API key. The free API allowance is shared by the account's keys, rather than being multiplied by generating another key. See the API documentation for inputs, outputs and limits.

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• Calibre comparison — a local desktop workflow.