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Technology · head to head

PostHog vs Sphinx

PostHog logo

PostHog

Technology

The single platform to analyze, test, observe, and deploy new features

From
Free
Rated
-
Full reviewWebsite
Sphinx logo

Sphinx

Documentation

Documentation generator built for large technical projects

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: PostHog the free tier covers 1M events, 5K web session recordings and 2.5K mobile recordings per month before usage-based billing starts; Sphinx reStructuredText is harder to write than Markdown and puts off contributors, though MyST now allows Markdown
  • They diverge on capability: PostHog covers Product analytics, Sphinx covers Cross-references.
  • Prices and features above were last checked on 30 August 2026.

Where they differ

Only the attributes on which PostHog and Sphinx actually diverge.

Attributes where PostHog and Sphinx differ
AttributePostHogSphinx
Pricing modelusage-basedOpen source, no licence fee
PlatformsWeb, Ios, Android, ApiLinux, macOS, Windows
CategoryTechnologyDocumentation
Founded2020Unknown

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 PostHog

  • Product analytics
  • Session recording
  • Feature flags
  • A/B testing
  • Heatmaps
  • SQL access
  • Data warehouse
  • Apps platform

Only in Sphinx

  • Cross-references
  • API autodoc
  • Multi-format output
  • Extension ecosystem

What people use each for

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

PostHog

  • Product analyticsnot Sphinx
  • Feature experimentationnot Sphinx
  • User behavior trackingnot Sphinx
  • A/B testingnot Sphinx
  • Debug production issuesnot Sphinx

Sphinx

  • Large technical documentation needing reliable cross-referencesnot PostHog
  • Python projects generating API docs from docstringsnot PostHog
  • Documentation that must ship as PDF as well as HTMLnot PostHog

Where each one falls short

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

PostHog

  • The free tier covers 1M events, 5K web session recordings and 2.5K mobile recordings per month before usage-based billing starts
  • Accounts without a card on file are limited to 1 project; adding one raises it to 6
  • Data retention is 1 year until a card is added, which extends it to 7 years
  • Support is community-only until the account is on a paid plan
  • Error tracking is capped at 100K exceptions and surveys at 1500 responses per month on the free tier

Sphinx

  • reStructuredText is harder to write than Markdown and puts off contributors, though MyST now allows Markdown
  • Configuration is complex and the default output is dated-looking without theme work
  • Build times on large documentation sets are slow
  • Heavier than the problem for a small project that only needs a few pages

Pricing, plan by plan

PostHog

Free
  • FreeFree
    • 1M events/month
    • 5K sessions/month
    • Unlimited users
  • Paid$undefined/month
    • $0.00031/event
    • $0.005/session
    • Advanced permissions
  • Enterprise$undefined/month
    • SAML SSO
    • Advanced security
    • Dedicated support

Sphinx

Free
  • SphinxFree
    • Full functionality
    • Commercial use permitted
    • Community support

Which should you pick?

Choose PostHog if

  • You need product analytics.
  • You want to start without paying.
  • You work on Web, Ios, Android, Api.
  • You also want session recording.
PostHog review

Choose Sphinx if

  • You need cross-references.
  • You want to start without paying.
  • You work on Linux, macOS, Windows.
  • You also want api autodoc.
Sphinx review

Questions people ask

Is PostHog or Sphinx better?
Neither clearly leads. PostHog starts at Free and Sphinx at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, PostHog or Sphinx?
PostHog starts at Free and Sphinx at Free.
Does PostHog or Sphinx run on more platforms?
PostHog runs on Web, Ios, Android, Api. Sphinx runs on Linux, macOS, Windows.
Can I use PostHog for free?
Both have a free tier, so you can try either at no cost before committing.
What is PostHog best used for?
PostHog is most often used for product analytics, feature experimentation, user behavior tracking, a/b testing. Of those, product analytics and feature experimentation are not what Sphinx is typically brought in for.
What can PostHog do that Sphinx cannot?
PostHog covers Product analytics, Session recording, Feature flags, A/B testing. Sphinx covers Cross-references, API autodoc, Multi-format output, Extension ecosystem.

Answered from the vendors’ own pages

PostHog: What does PostHog's free tier include per month?

PostHog free tier includes: 1M analytics events, 5K session replays, 1M feature flag requests, 100K error tracking exceptions, 1,500 survey responses, 1M data warehouse rows, 10K data pipeline events, 100K AI observability events, 500 PostHog AI credits, 10K workflow messages, and 10GB log ingestion. Source: https://posthog.com/pricing

Source
Sphinx: Is Sphinx free?

Yes, open source under the BSD licence.

PostHog: How much data retention does PostHog provide on paid plans?

PostHog free tier provides 1-year data retention. Pay-as-you-go plans offer 7-year data retention across all projects, enabling longer historical analysis. Source: https://posthog.com/pricing

Source
Sphinx: Do I have to write reStructuredText?

Not any more. The MyST extension allows Markdown, though reStructuredText remains the native format and most examples use it.

PostHog: What percentage of PostHog users stay on the free tier?

PostHog states that 97% of companies use PostHog for free, indicating extensive free tier adoption. However, specific per-unit pricing rates for overages on paid plans are not published. Source: https://posthog.com/pricing

Source
Sphinx: Why do large projects choose Sphinx?

Automatic cross-referencing and API extraction from docstrings, which lighter generators do not provide.

PostHog: When does PostHog provide priority support on paid plans?

PostHog provides email or Slack support for accounts exceeding $2,000/month on pay-as-you-go plans. Specific response times and support SLAs are not detailed on their pricing page. Source: https://posthog.com/pricing

Source
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