Agent Passport

"Agent passport" isn't the name of a single ratified spec: it's the plain-English label the AI-agent field has converged on for a pattern: give an autonomous agent a portable, checkable identity that outlives any one platform, so a stranger can look it up and answer "who owns this, and does it have a track record?" without taking the agent's own word for it. The word "passport" is doing real work here: like a government passport, it's issued by someone other than its holder, and its value comes from a third party being able to verify it independently.

The concrete mechanism most of the field has actually converged on is ERC-8004's Identity Registry (see that entry), an ERC-721 NFT minted per agent, whose tokenURI points to an off-chain manifest describing the agent. That's a distinct, separate idea from Google's Agent2Agent (A2A) protocol's "AgentCard", a JSON document an agent serves about itself at a well-known URL, for capability discovery. The difference matters: an A2A AgentCard is self-declared (the agent's own claim about what it can do), while an ERC-8004 passport is a third-party-checkable on-chain record (an independent registry says this identity exists and this address controls it). The two can compose (an on-chain passport can point to an off-chain AgentCard) but they answer different questions.

Where it comes from

Neither pattern is Solidus's invention. ERC-8004 (see that entry) is an open Ethereum standard co-authored by contributors from MetaMask, the Ethereum Foundation, Google, and Coinbase. A2A's AgentCard is a Google-originated concept from a separate protocol family for agent-to-agent messaging. Solidus composes both ideas: it issues a did:solidus identity and a BBS+ capability credential to an agent, then anchors both to an ERC-8004 passport it mints: its own manifest format for that passport is called a "SolidusAgentCard," a name that borrows the "Card" convention loosely without being the same artifact as A2A's.

Solidus status

One real passport exists today: token 8064 on Base Sepolia (a public testnet, not Ethereum mainnet), minted by Solidus's agent-identity SDK. Its tokenURI resolves to a SolidusAgentCard JSON document naming the agent's did:solidus DID and its ERC-8004 anchor details.

One live discrepancy is worth flagging plainly rather than smoothing over: as of this writing, that same SolidusAgentCard JSON still describes its DID method's registry status as "submitted... under review, not yet registered." That's stale, did:solidus was actually registered in the W3C DID Method Registry on 2026-07-04 (see that entry), the card simply hasn't been updated to reflect it. This runs on Solidus's public testnet only, and the did:solidus↔ERC-8004 pairing has not been used by a real, paying agent operator yet.

Proof you can run yourself: curl https://agents.solidus.network/v1/agents/d7b2f0ed-a5ba-4c48-a3af-7c14e8070b20/card returns the live SolidusAgentCard JSON. Cross-checked directly against the chain, tokenURI(8064) on Base Sepolia's Identity Registry returns exactly that URL, and ownerOf(8064) returns the same owner address the card names. A stranger can verify the on-chain and off-chain halves agree with each other without trusting either half alone.