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AI · head to head

Helicone vs Sigil

Helicone logo

Helicone

AI

Open-source LLM observability and gateway platform for AI applications

From
Free
Rated
-
Full reviewWebsite
Sigil logo

Sigil

Publishing

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

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Helicone the free Hobby plan is capped at 10,000 requests per month, which teams with production traffic can exceed quickly.; Sigil it produces no print output whatever, so any book that needs a paperback interior requires a completely separate tool and a second workflow.
  • They diverge on capability: Helicone covers Request dashboard and tracking, Sigil covers Direct EPUB editing.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which Helicone and Sigil actually diverge.

Attributes where Helicone and Sigil differ
AttributeHeliconeSigil
Pricing modelfreemiumOpen source, no licence fee
Platformsweb, apiWindows, macOS, Linux
CategoryAIPublishing

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 Helicone

  • Request dashboard and tracking
  • Sessions and segments
  • Helicone Query Language (HQL)
  • Prompt datasets and improvement
  • Playground
  • Rate limits and alerts

Only in Sigil

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

What people use each for

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

Helicone

  • Monitoring cost and latency of production LLM applicationsnot Sigil
  • Debugging multi-step agent sessionsnot Sigil
  • Managing and iterating on prompts across a teamnot Sigil
  • Routing requests across multiple LLM providersnot Sigil

Sigil

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

Where each one falls short

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

Helicone

  • The free Hobby plan is capped at 10,000 requests per month, which teams with production traffic can exceed quickly.
  • Advanced compliance features like SOC 2 and HIPAA are only available starting at the $799/month Team plan.
  • Usage beyond the free tier is billed on top of the base subscription, adding cost unpredictability at scale.
  • On-premises deployment is restricted to the custom Enterprise tier.

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.

Pricing, plan by plan

Helicone

Free
  • HobbyFree
    • 10,000 free requests
    • 1 GB storage
    • 1 seat
  • Pro$79/month
    • 10K free requests included, usage-based beyond
    • 7-day free trial
    • Unlimited playgrounds and workspaces
  • Team$799/month
    • 5 organizations
    • SOC 2 and HIPAA compliance
    • Dedicated Slack channel access
  • Enterprise$undefined/mo
    • Custom MSAs and SAML SSO
    • On-premises deployment
    • Bulk cloud discounts

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

Which should you pick?

Choose Helicone if

  • You need request dashboard and tracking.
  • You want to start without paying.
  • You work on web, api.
  • You also want sessions and segments.
Helicone review

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

Questions people ask

Is Helicone or Sigil better?
Neither clearly leads. Helicone starts at Free and Sigil at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Helicone or Sigil?
Helicone starts at Free and Sigil at Free.
Does Helicone or Sigil run on more platforms?
Helicone runs on web, api. Sigil runs on Windows, macOS, Linux.
Can I use Helicone for free?
Both have a free tier, so you can try either at no cost before committing.
What is Helicone best used for?
Helicone is most often used for monitoring cost and latency of production llm applications, debugging multi-step agent sessions, managing and iterating on prompts across a team, routing requests across multiple llm providers. Of those, monitoring cost and latency of production llm applications and debugging multi-step agent sessions are not what Sigil is typically brought in for.
What can Helicone do that Sigil cannot?
Helicone covers Request dashboard and tracking, Sessions and segments, Helicone Query Language (HQL), Prompt datasets and improvement. Sigil covers Direct EPUB editing, Code and preview views, EPUB 2 and EPUB 3, Regex across files.

Answered from the vendors’ own pages

Helicone: What does Helicone cost?

Helicone offers a free Hobby plan, a Pro plan at $79/month, a Team plan at $799/month, and custom Enterprise pricing, with usage-based charges applying beyond included request limits.

Source
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.

Helicone: Is there a free plan, and what are its limits?

The free Hobby plan includes 10,000 requests per month, 1 GB of storage, 1 seat, and 1 organization, aimed at kickstarting AI projects.

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.

Helicone: Are there discounts available?

Helicone offers 50% off the first year for qualifying startups, discounts for non-profits, a $100 annual credit for open-source projects, and free access for students.

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.

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