A2A is a protocol for stitching ownership boundaries together
A2A (Agent2Agent) is an open protocol for connecting agents built on different frameworks, even when they do not belong to the same organization. According to the Linux Foundation, A2A grew from 50 to more than 150 supporting organizations within a year of launch, and v1.0 delivered signed Agent Cards, the AP2 payment protocol, and SDKs in five languages. The core idea is to treat each agent not as a standalone service but as a trust-boundary unit, and to explicitly verify identity and authority on every call that crosses a boundary.
Signed Agent Cards are the starting point of verification
An Agent Card is a metadata document describing an agent's name, capabilities, endpoints, and authentication methods. A signed Agent Card adds an issuer signature so a caller can confirm the counterpart has not been forged before making a call. In operations, treat signature-verification failure as an immediate block reason; for expired or revoked cards, re-fetch and retry, but route to a human-confirmation queue after consecutive failures.
AP2 turns payment authority into a delegatable unit
The AP2 payment protocol structures the authority and limits an agent needs when initiating a payment on a user's behalf. By specifying amount caps, validity windows, and cancellation conditions, it blocks overcharging at the protocol level.
A full guide: from planning to operations
In the planning phase, partition the agents you will connect by trust boundary and fix target metrics as numbers. For example, set a baseline of p95 latency under 800ms for boundary-crossing calls, an Agent Card signature-verification pass rate of at least 99.5%, and zero unauthorized-payment violations.
Branch recovery differently by failure type. Block signature-verification failures immediately; for card expiry, re-fetch and retry once; for timeouts, retry up to three times with exponential backoff. If all retries fail, return a safe-reduced response with diminished capability, and never proceed with irreversible actions such as payments without human confirmation. If the boundary error rate exceeds 2% in a five-minute window, or over-limit payment attempts are detected three times in a row, circuit-break that boundary and send an alert.
Enforce standard logs as part of quality control. Record a correlation ID, calling-agent identity, Agent Card fingerprint, the decision (allow, block, or reduce), and latency as structured fields for every boundary call, while masking PII before storage. For the continuous-improvement loop, aggregate failure logs by type weekly, track the share recovered by retry versus escalated to human confirmation, and tune policy starting with the boundaries that recover least. Since the Linux Foundation has signaled a joint MCP/A2A specification for Q3 2026, align the log schemas for tool calls and inter-agent calls now.
Executive summary
A2A connects agents as trust-boundary units, verifying identity with signed Agent Cards and payment authority with AP2. Design failure branches before the happy path, put standard logs and stop conditions in place, and only then widen the scope of automation.