Threshold custody · open source

Your secret, split into shards.

Split any sensitive secret — seed phrase, private key, password, or recovery code — into M-of-N shards. Any M can recover it. Fewer than M reveal nothing.

Split a secret → Recover a secret
Read the security model →
Browser-only Open source No server storage Quantum-safe threshold
Secret f(0)
Shamir Secret Sharing
f(x) = secret + a₁x + a₂x²
i
ii
iii
iv
v
Any 3 of 5 reconstruct
Procedure

How it works.

Four steps, performed entirely inside your browser. No account, no upload, no server-side processing.

i · Enter

Enter your secret

Seed phrase, private key, password, recovery code, or any short text up to 4 KB.

ii · Choose

Choose threshold

Pick 2-of-3, 3-of-5, 5-of-7, or any custom M-of-N up to your tier limit.

iii · Distribute

Store separately

Print, engrave, write down, or distribute to trusted holders. Never store all shards together.

iv · Recover

Recover when needed

Any M shards reconstruct the original secret locally in the browser. Fewer than M reveal nothing.

Applications

For when a single point of failure is unacceptable.

Crypto inheritance

3-of-5

Pass on a self-custody wallet to family without giving any single person full access during your lifetime.

Recommended holders
SpouseAdult childLawyerSafe deposit boxExecutor

Password vault backup

2-of-3

Protect access to your password manager's master key against device loss, fire, or single-point compromise.

Recommended holders
Home safeTrusted personBank deposit box

DAO & protocol treasury

5-of-7

Threshold backup for protocol-level recovery secrets. Distinct from operational multisig — for when signing keys must be reconstructed.

Recommended holders
Signers ×4FoundationCounselCommittee

Business continuity

3-of-5

Ensure operational secrets survive personnel changes, executive departures, or sudden incapacity of any one officer.

Recommended holders
CEOCFOCounselBoard memberCompany safe

Family office recovery

5-of-7

Distribute custody secrets across principal, fiduciaries, and counsel without granting any single party unilateral access.

Recommended holders
PrincipalTrusteeCounselFO directorCustodian

Emergency backup

2-of-3

The minimum viable backup for personal use. Survives one device loss or one location compromise.

Recommended holders
DeviceSafeTrusted person
Architecture

Security without custody.

  • Shards does not store your secret.
  • Shards does not store your shards.
  • Sensitive operations happen in your browser.
  • The source code is open and verifiable.
  • You can run it locally, fully offline.
Read the security model →
Browser
  • secret_input
  • shamir_split
  • shard_generation
  • pdf_render
  • recovery
Server
  • static_files
  • html · css · js
  • fonts · icons
  • — nothing else —
Never transmitted
secret shards reconstructed_secret
Mathematics

Fewer than M shards reveal nothing.

Information-theoretic security: the threshold split itself does not depend on computational hardness.

# the secret is the constant term of a polynomial secret = f(0) # a polynomial of degree M−1 is constructed f(x) = secret + a1x + a2x2 # N shards are points on the polynomial shards = f(1), f(2), f(3), f(4), f(5) # any M points fully determine f, and therefore f(0) recover = any 3 points → f(0)
In a 3-of-5 setup, two shards are not almost enough. They reveal nothing useful.
Tiers

Honest pricing.

The core protocol is free, browser-only, and open source. Paid tiers fund maintenance, audits, and premium templates.

Personal

For individuals protecting their own backups

Free
forever · no account
  • Up to 3-of-5 thresholds
  • Browser-only splitting
  • Printable cards (minimal)
  • Recovery tool included
  • Open-source source code
Start splitting
Coming soon

Guardian

For inheritance, families, small teams

$49/yr
single-user · annual
  • Up to 7-of-11 thresholds
  • Premium card templates
  • Holder instruction packs
  • Offline deployment package
  • Recovery checklist & rehearsal
Notify me
Coming soon

Institutional

For family offices, protocols, custodians

$490+
custom · contact us
  • Threshold ceremony templates
  • Offline deployment package
  • Audit documentation
  • Family office & protocol support
  • Bring-your-own audit firm
Speak with us
Frequently asked

Things people ask.

No. Shards never receives or stores your secret or your shards. Recovery requires possession of any M of the N shards you generated. If those are lost, the secret cannot be recovered — by us or anyone.
If you fall below the threshold M, the secret is mathematically unrecoverable. This is the same property that makes 2 or fewer shards reveal nothing. The privacy guarantee cuts both ways.
No — not unless they collude with enough other holders to meet the threshold. A single shard reveals nothing useful about the secret. This is the core property of Shamir's Secret Sharing.
The threshold split itself is information-theoretically secure: it does not depend on any computational hardness assumption, so a quantum computer gains no advantage. Other risks (malware, phishing, physical theft) are outside the cryptographic guarantee — see our security page for the precise threat model.
No. It works for any short secret: BIP-39 seed phrases, private keys, password manager master passwords, recovery codes, encryption keys, or arbitrary text up to 4 KB.
Yes, and we recommend it for high-value secrets. Load the page once, disconnect from the internet, then split or recover. The codebase can also be cloned and run locally — see the Security page for the verification procedure.
Begin

No single point of failure.

Split a secret → Recover a secret