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Research · head to head

Castor EDC vs Obsidian

Castor EDC logo

Castor EDC

Research

Electronic data capture and eConsent for clinical trials, built for investigator-initiated studies as well as sponsors

From
On request
Rated
-
Full reviewWebsite
Obsidian logo

Obsidian

Research

A powerful knowledge base on top of a local folder of plain text Markdown files

From
Free
Rated
-
Full reviewWebsite

The short version

  • Only Obsidian has a free tier, so it costs nothing to try first.
  • Each has a real cost: Castor EDC nothing is published: pricing is quoted only after a scoping call and protocol review, so budgeting a grant application means asking for a quote months before the study is funded and hoping the scope holds.; Obsidian sync is a paid add-on at $4 per month billed annually rather than part of the app
  • They diverge on capability: Castor EDC covers Browser-based study build, Obsidian covers Bidirectional linking.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which Castor EDC and Obsidian actually diverge.

Attributes where Castor EDC and Obsidian differ
AttributeCastor EDCObsidian
Starting priceOn requestFree
Pricing modelquoteUnknown
Free tierNoYes
PlatformsWeb, iOS, AndroidWeb, Windows, macOS, Linux, iOS, Android
FoundedUnknown2020

Identical on both: user rating (Not yet rated), category (Research).

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 Castor EDC

  • Browser-based study build
  • 21 CFR Part 11 workflows
  • eConsent
  • ePRO and surveys
  • Randomisation
  • Per-study licensing
  • Grant-funded pricing paths
  • Data export

Only in Obsidian

  • Bidirectional linking
  • Graph view visualization
  • Markdown support
  • Local file storage
  • Plugin ecosystem
  • Custom CSS themes
  • Templates
  • Search and tags

What people use each for

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

Castor EDC

  • An academic hospital running an investigator-initiated trial that cannot fund a sponsor-grade EDC contract or a data management CROnot Obsidian
  • A medical device company collecting post-market clinical follow-up data with Part 11 audit trailsnot Obsidian
  • A multi-site registry that needs remote eConsent because participants are recruited nationally rather than at a clinicnot Obsidian
  • A biotech running a small phase two study that wants the database built by its own clinical team in weeks rather than commissionednot Obsidian

Obsidian

  • Local-first markdown note taking with no account requirednot Castor EDC
  • Linking notes into a personal knowledge graphnot Castor EDC
  • Syncing a vault across devices with end-to-end encryption on the paid add-onnot Castor EDC
  • Publishing a public site from a vaultnot Castor EDC
  • Extending the editor with community pluginsnot Castor EDC

Where each one falls short

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

Castor EDC

  • Nothing is published: pricing is quoted only after a scoping call and protocol review, so budgeting a grant application means asking for a quote months before the study is funded and hoping the scope holds.
  • Price scales on protocol complexity rather than a simple unit, so two studies with the same participant count can be quoted very differently and there is no public benchmark to argue against.
  • Modules such as eConsent, ePRO and randomisation are quoted on top of the base platform, so the headline EDC figure is rarely the number that appears on the final proposal.
  • It is deliberately lighter than the full sponsor suites, so a study that grows into a global registrational programme needing integrated CTMS, safety, IRT and full trial supply management will need additional systems and the interfaces between them.
  • Regulatory responsibility does not transfer with the software: the platform supports Part 11 compliant workflows, but system validation for your intended use, SOPs and audit readiness remain your obligation and your cost, which sponsors new to EDC consistently underestimate.

Obsidian

  • Sync is a paid add-on at $4 per month billed annually rather than part of the app
  • Publishing to the web is a further $8 per month per site
  • Commercial use asks for a $50 per user per year licence, though the vendor states it is not required
  • Collaboration is limited compared with a hosted notes tool, since the vault is local files first

Pricing, plan by plan

Castor EDC

On request
  • Castor EDC$undefined/year
    • Priced per study on protocol complexity, duration, sites and modules
    • 21 CFR Part 11 and ICH GCP workflows
    • eConsent, ePRO and randomisation modules quoted separately

Obsidian

Free
  • Obsidian Sync$4/month
    • Sync notes across devices
  • Obsidian Publish$8/month
    • Turn notes into a website

Which should you pick?

Choose Castor EDC if

  • You need browser-based study build.
  • You work on Web, iOS, Android.
  • You also want 21 cfr part 11 workflows.
Castor EDC review

Choose Obsidian if

  • You need bidirectional linking.
  • You want to start without paying.
  • You work on Web, Windows, macOS, Linux, iOS, Android.
  • You also want graph view visualization.
Obsidian review

Questions people ask

Is Castor EDC or Obsidian better?
Neither clearly leads. Castor EDC starts at On request and Obsidian at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Castor EDC or Obsidian?
Obsidian has a free tier; the other does not. Paid plans start at On request for Castor EDC and Free for Obsidian.
Does Castor EDC or Obsidian run on more platforms?
Castor EDC runs on Web, iOS, Android. Obsidian runs on Web, Windows, macOS, Linux, iOS, Android.
Can I use Obsidian for free?
Yes. Obsidian has a free tier, so you can try it without paying. Castor EDC starts at On request.
What is Castor EDC best used for?
Castor EDC is most often used for an academic hospital running an investigator-initiated trial that cannot fund a sponsor-grade edc contract or a data management cro, a medical device company collecting post-market clinical follow-up data with part 11 audit trails, a multi-site registry that needs remote econsent because participants are recruited nationally rather than at a clinic, a biotech running a small phase two study that wants the database built by its own clinical team in weeks rather than commissioned. Of those, an academic hospital running an investigator-initiated trial that cannot fund a sponsor-grade edc contract or a data management cro and a medical device company collecting post-market clinical follow-up data with part 11 audit trails are not what Obsidian is typically brought in for.
What can Castor EDC do that Obsidian cannot?
Castor EDC covers Browser-based study build, 21 CFR Part 11 workflows, eConsent, ePRO and surveys. Obsidian covers Bidirectional linking, Graph view visualization, Markdown support, Local file storage.

Answered from the vendors’ own pages

Castor EDC: Is there a free academic version?

No published free tier. There are academic, non-profit and grant-funded pricing paths, but each is quoted rather than self-service.

Obsidian: Is Obsidian free?

Yes. The core Obsidian application is 100% free for personal and commercial use with no limitations. You can use unlimited vaults and every core feature without payment.

Source
Castor EDC: Is it 21 CFR Part 11 compliant?

It supports Part 11 compliant workflows with audit trails and electronic signatures. Validating the system for your specific use remains your responsibility.

Obsidian: What file format does Obsidian use?

Obsidian stores every note as a plain Markdown file. Because it uses standard Markdown instead of a proprietary format, your notes remain portable and can be edited with many other Markdown editors.

Source
Castor EDC: Do I need a programmer to build a study?

No. Case report forms are configured in the browser, which is the main reason academic groups adopt it.

Obsidian: Can I collaborate with others in Obsidian?

The core application does not include built-in team collaboration features. However, Obsidian offers optional add-ons and can be used with version control systems or cloud storage for collaboration.

Source
Castor EDC: How long does a quote take?

Castor states a full pricing proposal within five business days of sharing the protocol.

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