What is a trust registry for AI agents?

A trust registry answers "should I trust whoever issued this": a different question from ERC-8004's own Reputation Registry, which answers "has this specific agent performed well." They're related. They are not the same registry, and conflating them is the first mistake a careless writer makes on this topic.

The general Trust Registry concept

A Trust Registry is infrastructure that answers a question cryptography alone can't: not "is this credential genuine", a signature settles that, but "should I trust whoever issued it?" Anyone can issue a credential claiming "verified: yes." A trust registry is a public, queryable list of which issuers are actually accredited, and at what strength of check.

The mechanism that makes this accountability real rather than decorative is de-listing. If an issuer turns out to be careless or fraudulent, removing it from the registry flips every subsequent verification of that issuer's credentials to reject, network-wide, without any verifier needing to individually blocklist that issuer itself. The Trust over IP Foundation formalized the general pattern; the EU's eIDAS "Trusted Lists" and EBSI's Trusted Issuers Registry are both deployed examples of the same idea at nation-state scale. Solidus composes this general pattern: it did not invent the concept of a trust registry, and it does not implement ToIP's or EBSI's specific protocol wire format.

ERC-8004's Reputation Registry, precisely

ERC-8004, the Ethereum standard behind the agent passport, defines its own, separate registry that answers a different question entirely. Its Reputation Registry lets clients who've actually used an agent leave on-chain feedback about that agent's performance: did it do the job it was asked to do, and do it well? That's client-reported track record for one specific agent, not a check on who accredited the agent's issuer. See What is ERC-8004? for the standard's full architecture, including its sibling Validation Registry, which attaches cryptographic proof that a specific agent action was checked, a third distinct question again.

Neither of ERC-8004's own registries is a trust registry in the general sense described above. Reputation Registry entries are about the agent's behavior. A trust registry entry is about the issuer standing behind the agent's credentials.

Where they intersect for an agent's identity

A relying party evaluating whether to deal with an agent might reasonably check both. Is the issuer of this agent's credentials, its operator's KYC credential, say (see Operator KYC for AI agents), actually accredited and in good standing? That's a Trust Registry question. Separately: has this specific agent, this specific token in the Identity Registry, performed well for other clients before? That's ERC-8004's own Reputation Registry question. Both matter to the same underlying decision, should I deal with this agent, but they're answered by different registries, maintained by different parties, and one answering "yes" says nothing about the other.

Solidus's own worked example

Solidus operates one live registry that illustrates the general Trust Registry mechanism, but it's worth being precise about which product it belongs to. The registry-read endpoint below is Solidus Verify Capture's, not this product's own:

curl https://capture-api.solidus.network/registry/issuers/did:solidus:testnet:1111111111111111111111zz
→ 404, {"message":"issuer not enrolled in this registry"}

That confirms the fail-closed behavior a trust registry needs: an unknown issuer is rejected outright, not treated as a soft miss. It's a real, live, checkable example of the general mechanism this page describes, a public, queryable issuer list with de-listing as its accountability lever, borrowed here from a sibling Solidus product because no agents.solidus.network-specific registry-read endpoint exists as of this writing. If a relying party wants to check the accreditation of an agent's credential issuer today, this cross-product endpoint is the concrete answer; there is no agents-specific equivalent yet.

The honesty line

Today Solidus operates a single, Solidus-controlled registry, not a federation of registries that recognize each other the way the EU's Trusted Lists federate member states. De-listing power sits with Solidus alone right now, a centralization tradeoff worth naming rather than glossing over, the same tradeoff any single-operator trust registry carries until it federates.

Both halves of this run on public testnets. The registry read above is queried with a did:solidus:testnet: identifier, and the agent passports such a registry would vouch for are anchored on Base Sepolia. Nothing described on this page is on a mainnet.

Close

A trust registry and a reputation registry both help answer "can I deal with this agent", but they're answering different halves of that question, maintained by different mechanisms, and neither substitutes for the other. ERC-8004's Reputation Registry is client feedback about one agent's performance. A trust registry, general or Solidus's own, is a check on whether the issuer behind an agent's credentials is accountable at all.