What is Cosigni?

One of the most compelling arguments for choosing cryptocurrencies over traditional banking is self-custody. Combined with blockchain's decentralized design, it allows individuals to store their wealth without relying on intermediaries, shifting control back to users. But self-custody carries a significant responsibility, one that most average users are not equipped to handle.

The problem is not ignorance; it is fragility. Even if you use a hardware wallet, securely store your seed phrase, and follow best practices, a single wrong signature is often catastrophic. This, along with the difficulty of tracking and prosecuting thieves, makes self-custodied assets an exceptionally attractive target for attackers.

If you are new to Cosigni, this page explains what it is, why it exists, and how it can help you hold your own keys with more confidence.

Why one key is not enough

Most people self-custody their crypto in a simple wallet: a private key managed by software or hardware. The main line of defense is whatever the wallet shows you before you sign. That sounds reasonable until you realize how little that display actually tells you.

Complex transactions are compressed into a few cryptic lines on a tiny screen. A compromised wallet interface can show one thing while submitting something entirely different for signing. Your hardware device may never be hacked, and you can still lose everything, because humans are not equipped to detect malicious intent buried in raw call data.

Multisig wallets were supposed to fix this. Instead of one key, you split control across several independent signers. In theory, no single compromise should be enough. In practice, the ByBit heist showed what happens when every signer looks at the same compromised interface: three experienced operators approved a transaction they believed was routine, while the actual payload replaced the wallet's logic module. The theoretical security of "many keys" effectively disappeared, because the supply chain became a single point of failure.

What Cosigni is

Cosigni is a free AI co-signer for multisig wallets. It sits alongside your existing setup rather than inside it, operates independently from your wallet software, and holds part of the signing power so a compromised wallet cannot act alone.

When you send a transaction from a Safe or Ready multisig, Cosigni receives the pending request, shows you the raw transaction data, runs an AI safety assessment, and only co-signs when you explicitly approve. It does not hold your assets, cannot move funds on its own, and never changes your vault's threshold. It is one signer in your multisig, nothing more.

The closest comparison is using a second hardware device as a co-signer. That helps with key separation, but it does not solve human fallibility: the device still shows you the same misleading summary a compromised interface prepared. Cosigni is designed to address that gap. It reads the actual payload, flags suspicious patterns, and gives you a second opinion before any signature is submitted.

Any two of these three keys can move funds. Cosigni alone cannot. Your hardware wallet alone cannot. If the service is unavailable or you lose trust in it, your offline backup key remains an override. You keep control of the vault; Cosigni just makes blind signing harder.

How it works

Getting started takes a few minutes and does not require migrating your existing wallet:

1. Create an account and generate a cosigner. Sign up for Cosigni and create one or more cosigners for your multisig wallets. Each cosigner gets its own keypair; you use the public key when configuring your vault.
2. Link the cosigner to your vault. Add the cosigner's public key as an owner in your Safe or Ready multisig, then add the multisig address to the cosigner in Cosigni so it knows which vault to watch.
3. Review before you sign. When a transaction is proposed, Cosigni fetches the pending request, displays the raw payload, and sends it through an AI safety check. You see a verdict with reasoning before deciding whether to co-sign.
4. Co-sign only when you choose. Signing is always user-triggered. Cosigni recomputes the transaction hash before submitting and refuses mismatches.

Nothing about your day-to-day wallet usage needs to change dramatically. You still use your hardware wallet. You still control the threshold. Cosigni adds an independent review step between "someone proposed this transaction" and "enough signatures exist to execute it."

What you are not giving up

A fair question for any new security tool is what you trade away. Cosigni is deliberately limited:

• No custody. Your funds stay in your multisig. Cosigni never holds assets.
• No unilateral control. In a 2-of-3 setup, Cosigni cannot move funds without a second key.
• No vault migration. You add Cosigni as an owner in the multisig you already use.
• No privileged contract hooks. Cosigni works through standard signatures, not modules that could introduce new attack surface.

You are also not worse off for using it during normal operation. Every outgoing transaction gets an independent review of the raw call data, which limits the damage a compromised wallet UI or a simple mistake can cause.

Where Cosigni helps most

Consider the ByBit case again. Attackers injected malicious JavaScript into Safe's hosted frontend. Signers saw a routine internal transfer while the signing payload contained a delegatecall that swapped the wallet's logic module. Cosigni would have surfaced that raw calldata independently, before its signature was submitted, giving the team a chance to see the real operation instead of what the compromised interface displayed.

That is the core value proposition today: an independent second look at what you are actually signing, backed by AI-assisted analysis. Cosigni already ships the essentials for that workflow on mainnet. What follows is on the roadmap next.

Live today

Dedicated multisig signer. Cosigni generates a standard EVM or Starknet signer, stores the private key encrypted with AWS KMS, and submits a signature as one owner in your multisig.

Multi-chain support. Safe on EVM chains and Ready on Starknet, with chain-specific signer generation, pending request previews, and signature submission.

Raw calldata + AI review. Cosigni displays the raw pending transaction payload, sends it to Claude for a heuristic safety assessment, and returns a safe/caution verdict with confidence and reasoning.

Coming soon

Calldata decoding. Function-level decoding for approve, transferFrom, delegatecall, and other contract calls.

Simulation before signing. Fork simulation to preview on-chain effects before you co-sign.

Policy rules and automated approval. Spend limits, allowlisted destinations, velocity rules, and deterministic ERC-20/NFT approval checks.

Who is Cosigni for?

Cosigni is built for people who already self-custody meaningful amounts and want to take that setup further without giving up control. If you use a hardware wallet with a Safe or Ready multisig, hold assets across EVM chains or Starknet, and want a second factor that actually understands transaction content, Cosigni is for you.

It is free to use. There is no sales call, no waitlist, and no requirement to buy additional hardware. You add one more signer to a setup you already trust, and gain an independent review layer on every pending transaction.