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Publishing · head to head

Sigil vs Vellum

Sigil logo

Sigil

Publishing

Open source EPUB editor for working directly on the file, not generating it

From
Free
Rated
-
Full reviewWebsite
Vellum logo

Vellum

AI

Personalized AI assistant with persistent memory and autonomous action-taking

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Sigil it produces no print output whatever, so any book that needs a paperback interior requires a completely separate tool and a second workflow.; Vellum pricing varies significantly by computational tier, making budget planning difficult
  • They diverge on capability: Sigil covers Direct EPUB editing, Vellum covers Persistent AI identity.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which Sigil and Vellum actually diverge.

Attributes where Sigil and Vellum differ
AttributeSigilVellum
Pricing modelOpen source, no licence feeFreemium with paid plans and pay-as-you-go credits
PlatformsWindows, macOS, LinuxWeb, macOS, iOS, Slack, Telegram, Terminal
CategoryPublishingAI

Identical on both: starting price (Free), free tier (Yes), user rating (Not yet rated).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Sigil

  • Direct EPUB editing
  • Code and preview views
  • EPUB 2 and EPUB 3
  • Regex across files
  • Validation
  • Python plugins

Only in Vellum

  • Persistent AI identity
  • Long-term memory
  • Email automation
  • Calendar management
  • Autonomous task execution
  • Multi-device synchronization
  • Custom plugins
  • Open-source deployment

What people use each for

The jobs each tool is most often brought in to do.

Sigil

  • Fixing an EPUB that a retailer validator has rejected, without re-exporting from the tool that generated itnot Vellum
  • Correcting the table of contents, reading order or metadata in a file supplied by a conversion servicenot Vellum
  • Preparing a back-catalogue title where the only surviving source is the EPUB itselfnot Vellum
  • Applying a consistent stylesheet or a bulk text correction across every chapter of a book at oncenot Vellum

Vellum

  • Personal productivity automation across email and calendarnot Sigil
  • CRM updates and pipeline managementnot Sigil
  • Expense report generation and managementnot Sigil
  • Document drafting and content creationnot Sigil
  • Meeting scheduling and calendar coordinationnot Sigil

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Sigil

  • It produces no print output whatever, so any book that needs a paperback interior requires a completely separate tool and a second workflow.
  • Meaningful use requires reading and writing HTML and CSS, which puts it out of reach of most authors who simply want a finished file.
  • There is no cloud storage, sync or collaboration, so the book exists as a file on one machine and version control is whatever you set up yourself.
  • Development depends on a small number of volunteer maintainers, so release timing and platform builds follow their availability rather than a roadmap, and a lapse in maintenance would leave no obvious successor.
  • It provides no distribution, no retailer connection and no Kindle-native output, so it sits in the middle of a workflow that other tools have to complete on both sides.

Vellum

  • Pricing varies significantly by computational tier, making budget planning difficult
  • Requires explicit permission for sensitive actions, limiting autonomy
  • Self-hosting option may intimidate non-technical users
  • Learning curve to develop customizations with plugins

Pricing, plan by plan

Sigil

Free
  • SigilFree
    • GPL licensed with no cost or account required
    • Full functionality with no feature gating
    • Community support through forums and the issue tracker

Vellum

Free
  • FreeFree
    • Starter credits included
    • Basic features
  • Mighty$30/month
    • 1 vCPU, 2 GiB RAM
    • 10 GB storage
    • Included usage allowance
  • Super$100/month
    • 2.5 vCPU, 5 GiB RAM
    • 30 GB storage
    • Assistant email and subdomain
  • Ultra$200/month
    • 4 vCPU, 8 GiB RAM
    • 60 GB storage
    • Assistant email and subdomain

Which should you pick?

Choose Sigil if

  • You need direct epub editing.
  • You want to start without paying.
  • You work on Windows, macOS, Linux.
  • You also want code and preview views.
Sigil review

Choose Vellum if

  • You need persistent ai identity.
  • You want to start without paying.
  • You work on Web, macOS, iOS, Slack, Telegram, Terminal.
  • You also want long-term memory.
Vellum review

Questions people ask

Is Sigil or Vellum better?
Neither clearly leads. Sigil starts at Free and Vellum at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Sigil or Vellum?
Sigil starts at Free and Vellum at Free.
Does Sigil or Vellum run on more platforms?
Sigil runs on Windows, macOS, Linux. Vellum runs on Web, macOS, iOS, Slack, Telegram, Terminal.
Can I use Sigil for free?
Both have a free tier, so you can try either at no cost before committing.
What is Sigil best used for?
Sigil is most often used for fixing an epub that a retailer validator has rejected, without re-exporting from the tool that generated it, correcting the table of contents, reading order or metadata in a file supplied by a conversion service, preparing a back-catalogue title where the only surviving source is the epub itself, applying a consistent stylesheet or a bulk text correction across every chapter of a book at once. Of those, fixing an epub that a retailer validator has rejected, without re-exporting from the tool that generated it and correcting the table of contents, reading order or metadata in a file supplied by a conversion service are not what Vellum is typically brought in for.
What can Sigil do that Vellum cannot?
Sigil covers Direct EPUB editing, Code and preview views, EPUB 2 and EPUB 3, Regex across files. Vellum covers Persistent AI identity, Long-term memory, Email automation, Calendar management.

Answered from the vendors’ own pages

Sigil: Can I write my book in Sigil?

You can, but you should not. It is an EPUB editor, not a word processor, and writing long-form prose in it is unpleasant. Write elsewhere, import, then finish in Sigil.

Vellum: How does Vellum protect my data privacy?

Vellum uses permission-based controls requiring explicit approval for sensitive actions. Data is encrypted and the option for self-hosting provides complete data control. Open-source deployment option allows hosting on your own infrastructure.

Source
Sigil: Does it make Kindle files?

Not natively. Produce a valid EPUB in Sigil and let Amazon convert it, or use a separate conversion tool for other Kindle formats.

Vellum: Can I use Vellum for business team collaboration?

Vellum is primarily designed as a personal assistant with persistent identity. For team collaboration, platforms like Lindy offer better multi-user features with shared credit pools and Slack workspace integration.

Source
Sigil: Is it safe to rely on a volunteer project for commercial work?

The files it produces are standard EPUB, so nothing is locked in. The risk is that maintenance stops, not that your books become unreadable.

Vellum: What does the free tier include?

Vellum offers free starter credits to begin using the platform. Beyond that, it operates on a pay-as-you-go credit model with paid tiers starting at $30/month for increased computational resources and bundled credits.

Source
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