Cybersecurity · head to head
Cosign vs PartyKit
Cosign
Cybersecurity
Signs and verifies container images and artifacts, with or without managing keys
- From
- Free
- Free plan
- Yes
PartyKit
Developer Tools
Platform for building and deploying realtime multiplayer servers on the edge
- From
- Free
- Free plan
- Yes
The short version
- Each has a real cost: Cosign keyless signing inherits every weakness of the identity provider behind it. Sigstore’s own threat model states that if an identity provider is compromised, Sigstore will issue certificates to those identities, so a compromised account produces perfectly valid signatures.; PartyKit documentation and FAQ material on the marketing site is sparse compared to larger realtime platforms.
- They diverge on capability: Cosign covers Keyless signing, PartyKit covers Stateful edge servers.
- Prices and features above were last checked on 31 August 2026.
Where they differ
Only the attributes on which Cosign and PartyKit actually diverge.
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 Cosign
- Keyless signing
- Key and KMS signing
- Registry-native storage
- In-toto attestations
- Offline verification
- Trusted root and signing config
Only in PartyKit
- Stateful edge servers
- WebSocket-first API
- CRDT library compatibility
- Framework integrations
- Global edge deployment
- Custom domains
What people use each for
The jobs each tool is most often brought in to do.
Cosign
- Signing container images in a build pipeline without managing long-lived private keysnot PartyKit
- Attaching a signed bill of materials to a release so consumers can verify its provenancenot PartyKit
- Meeting a customer or regulatory requirement for signed artifactsnot PartyKit
- Verifying third-party images before they enter an internal registrynot PartyKit
PartyKit
- Multiplayer collaborative appsnot Cosign
- Realtime AI agent backendsnot Cosign
- Live cursors and presencenot Cosign
- Collaborative whiteboards and documentsnot Cosign
Where each one falls short
Documented limitations, not opinions. Every one is a constraint you would hit in normal use.
Cosign
- Keyless signing inherits every weakness of the identity provider behind it. Sigstore’s own threat model states that if an identity provider is compromised, Sigstore will issue certificates to those identities, so a compromised account produces perfectly valid signatures.
- A signature proves who signed, never whether they should have. The documentation is explicit that Sigstore cannot determine authorisation, so every consumer must write and maintain their own identity and issuer policy or verification means nothing.
- Nothing is enforced without an admission controller. Signing changes what you can prove, not what runs, and the official policy controller has a small maintainer base for a component sitting in a cluster admission path.
- Upgrades break pipelines. Version 3 changed defaults, version 4 is announced as removing legacy functionality and roughly half the command line flags, and two official client libraries still lacked support for the new log format as of mid 2026.
- Signatures do not expire. An artifact signed before a maintainer account was compromised and one signed after are indistinguishable unless somebody is actively monitoring the transparency log, and almost nobody is.
PartyKit
- Documentation and FAQ material on the marketing site is sparse compared to larger realtime platforms.
- Commercial free tier requires deploying to the user's own Cloudflare account, adding setup complexity.
- Storage on the free Individual plan clears every 24 hours, limiting it to prototyping rather than persistent production data.
- Smaller ecosystem and community than more established realtime infrastructure providers.
Pricing, plan by plan
Cosign
Free- CosignFree
- Apache-2.0
- Public Sigstore infrastructure free to use
- No usage limits published
PartyKit
Free- IndividualFree
- Up to 10 live projects
- Deploy to the global edge platform
- Storage clears every 24 hours
- CommercialFree
- Unlimited projects
- Custom domains
- Runs on your own Cloudflare account; pay only Cloudflare usage
Which should you pick?
Choose Cosign if
- You need keyless signing.
- You want to start without paying.
- You work on macOS, Linux, Windows, Docker.
- You also want key and kms signing.
Choose PartyKit if
- You need stateful edge servers.
- You want to start without paying.
- You work on web, api.
- You also want websocket-first api.
Questions people ask
- Is Cosign or PartyKit better?
- Neither clearly leads. Cosign starts at Free and PartyKit at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
- Which is cheaper, Cosign or PartyKit?
- Cosign starts at Free and PartyKit at Free.
- Does Cosign or PartyKit run on more platforms?
- Cosign runs on macOS, Linux, Windows, Docker. PartyKit runs on web, api.
- Can I use Cosign for free?
- Both have a free tier, so you can try either at no cost before committing.
- What is Cosign best used for?
- Cosign is most often used for signing container images in a build pipeline without managing long-lived private keys, attaching a signed bill of materials to a release so consumers can verify its provenance, meeting a customer or regulatory requirement for signed artifacts, verifying third-party images before they enter an internal registry. Of those, signing container images in a build pipeline without managing long-lived private keys and attaching a signed bill of materials to a release so consumers can verify its provenance are not what PartyKit is typically brought in for.
- What can Cosign do that PartyKit cannot?
- Cosign covers Keyless signing, Key and KMS signing, Registry-native storage, In-toto attestations. PartyKit covers Stateful edge servers, WebSocket-first API, CRDT library compatibility, Framework integrations.
Answered from the vendors’ own pages
Cosign: Does Cosign tell me if an image is vulnerable?
No. It has no vulnerability knowledge whatsoever. It can carry an SBOM as a signed attestation but never reads it. Pair it with a scanner.
PartyKit: How much does PartyKit cost?
PartyKit is completely free. Both the Individual and Commercial plans have no upfront costs.
SourceCosign: Is signing alone enough?
No. Verification is a command somebody runs. Without an admission controller enforcing it, an unsigned image still runs.
PartyKit: What is PartyKit's Individual plan?
The Individual plan is free and includes deployment to a global edge platform, support for up to 10 live projects, and is suitable for small projects. Storage is cleared every 24 hours.
SourceCosign: What does a bare cosign verify actually prove?
Very little. Without a pinned certificate identity and OIDC issuer, it accepts a valid signature from any identity at all.
PartyKit: What is PartyKit's Commercial plan?
The Commercial plan is free but requires deploying to your own Cloudflare account. It includes custom domains, unlimited projects, and you pay only your Cloudflare usage costs.
SourceCosign: What is the risk of keyless signing?
Your OIDC provider becomes the root of trust. Compromise of that account yields genuine, verifiable signatures, so account security is the control that matters.
PartyKit: Can I upgrade from Individual to Commercial plan?
Yes, both plans are free but offer different feature sets. The Commercial plan removes project restrictions but requires managing your own Cloudflare infrastructure.
SourceCosign: Should we expect breaking changes?
Yes. Version 4 is announced to remove roughly half the flags, and a post-quantum migration is named as a further breaking change after that.
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