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Cybersecurity · head to head

Sigstore vs Skopeo

Sigstore logo

Sigstore

Cybersecurity

Free public signing and transparency infrastructure for open source artifacts

From
Free
Rated
-
Full reviewWebsite
Skopeo logo

Skopeo

Cloud

Inspect, copy and sign container images without pulling them

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Sigstore the security model depends on somebody watching the log. The documentation states that compromise of an identity provider or of Fulcio itself is detectable only if third parties monitor the transparency log, the monitoring tool is a community-tier rather than core project, and almost no consumer runs one.; Skopeo single-purpose: it neither builds nor runs images, so it is one tool in a chain rather than a solution
  • They diverge on capability: Sigstore covers Fulcio, Skopeo covers Remote inspection.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which Sigstore and Skopeo actually diverge.

Attributes where Sigstore and Skopeo differ
AttributeSigstoreSkopeo
Pricing modelOpen source, public instance free to useOpen source, no licence fee
PlatformsWeb, Linux, macOS, Windows, Self-hostedLinux, macOS
CategoryCybersecurityCloud

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 Sigstore

  • Fulcio
  • Rekor
  • Keyless signing
  • Multi-language clients
  • Timestamp authority
  • Neutral governance

Only in Skopeo

  • Remote inspection
  • Registry-to-registry copy
  • Format conversion
  • Image signing

What people use each for

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

Sigstore

  • Open source projects signing releases without running a certificate authoritynot Skopeo
  • Organisations meeting a signed-artifact requirement without buying a signing productnot Skopeo
  • Publishing provenance that a consumer can verify independently of younot Skopeo
  • Self-hosting the same components where a public log is unacceptablenot Skopeo

Skopeo

  • Promoting images between staging and production registries without a round tripnot Sigstore
  • Inspecting an image’s contents before deciding to deploy itnot Sigstore
  • Mirroring images into an air-gapped or internal registrynot Sigstore

Where each one falls short

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

Sigstore

  • The security model depends on somebody watching the log. The documentation states that compromise of an identity provider or of Fulcio itself is detectable only if third parties monitor the transparency log, the monitoring tool is a community-tier rather than core project, and almost no consumer runs one.
  • It is a 99.5 percent objective with no service level agreement, which permits several hours of downtime a month and offers no remedy. A pipeline that signs on every build has taken a hard dependency on a free service with no contract behind it.
  • Log scale is a live engineering problem rather than a theoretical one. The active shard holds billions of entries, the log has already been sharded twice, and sharding version 1 requires stopping traffic, which is why a replacement was built.
  • Ten-minute certificates make trust depend on log availability. Verifying an older signature relies on the log entry proving it was made inside that window, so a lost or unreachable entry can render a valid artifact unverifiable.
  • Migration debt is substantial and ongoing. Version 2 of the log is generally available but not the public default, the signing client has an announced breaking release ahead, some official clients lag the new log format, and a post-quantum migration is named as the next break after that.

Skopeo

  • Single-purpose: it neither builds nor runs images, so it is one tool in a chain rather than a solution
  • Command syntax with transport prefixes such as docker:// is unusual and trips people up initially
  • Documentation is sparse compared with the rest of the container ecosystem

Pricing, plan by plan

Sigstore

Free
  • Public good instanceFree
    • Free to everyone with no contract
    • 99.5 percent availability objective, not an agreement
    • 100KB cap per attestation upload
  • Self-hostedFree
    • Apache-2.0
    • Run your own Fulcio and Rekor
    • Rekor v2 available for self-hosters

Skopeo

Free
  • SkopeoFree
    • Full functionality
    • No usage limits
    • Community support

Which should you pick?

Choose Sigstore if

  • You need fulcio.
  • You want to start without paying.
  • You work on Web, Linux, macOS, Windows, Self-hosted.
  • You also want rekor.
Sigstore review

Choose Skopeo if

  • You need remote inspection.
  • You want to start without paying.
  • You work on Linux, macOS.
  • You also want registry-to-registry copy.
Skopeo review

Questions people ask

Is Sigstore or Skopeo better?
Neither clearly leads. Sigstore starts at Free and Skopeo at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Sigstore or Skopeo?
Sigstore starts at Free and Skopeo at Free.
Does Sigstore or Skopeo run on more platforms?
Sigstore runs on Web, Linux, macOS, Windows, Self-hosted. Skopeo runs on Linux, macOS.
Can I use Sigstore for free?
Both have a free tier, so you can try either at no cost before committing.
What is Sigstore best used for?
Sigstore is most often used for open source projects signing releases without running a certificate authority, organisations meeting a signed-artifact requirement without buying a signing product, publishing provenance that a consumer can verify independently of you, self-hosting the same components where a public log is unacceptable. Of those, open source projects signing releases without running a certificate authority and organisations meeting a signed-artifact requirement without buying a signing product are not what Skopeo is typically brought in for.
What can Sigstore do that Skopeo cannot?
Sigstore covers Fulcio, Rekor, Keyless signing, Multi-language clients. Skopeo covers Remote inspection, Registry-to-registry copy, Format conversion, Image signing.

Answered from the vendors’ own pages

Sigstore: Is the public instance really free?

Yes, with no contract and no paid tier. That is also the weakness: a 99.5 percent objective with no agreement, no remedy and support through Slack.

Skopeo: Is Skopeo free?

Yes, open source with no licence fee.

Sigstore: Has the public log moved to Rekor v2?

No. Version 2 reached general availability in October 2025 and self-hosters can use it, but the public instance still defaults to version 1 and the project has said it will for the foreseeable future.

Skopeo: Why copy images without pulling them?

A registry-to-registry copy avoids downloading and re-uploading gigabytes, which is faster and much cheaper on bandwidth in CI.

Sigstore: Does Sigstore make my dependencies safe?

No, and this is a category error worth avoiding. It tells you who published something. It has no knowledge of what the artifact contains or whether it is vulnerable.

Skopeo: Can Skopeo run containers?

No. It only inspects, copies, signs and deletes images. Running them is Podman’s or Docker’s job.

Sigstore: What are the rate limits?

Not published. Only the 100KB cap per attestation upload is documented, so do not design a high-volume pipeline around assumed throughput.

Sigstore: Should we self-host it?

If a public record of every signature is unacceptable, or if a free service with no agreement cannot sit in your build path, then yes. Otherwise the public instance is what most projects use.

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