Autonomous agents are moving from prototypes to production across cloud platforms, enterprises and decentralised environments. As populations of agents expand across diverse systems, discovery, identity and capability sharing become foundational. Conventional mechanisms designed for static services and ownership-based trust struggle with agents that change locations, rotate capabilities and collaborate ephemerally. A new class of registry models is emerging to meet these demands with dynamic discovery, verifiable metadata and privacy-aware interactions. A comparative view of leading approaches highlights how design choices around security, authentication, scalability and maintenance shape suitability for different contexts, from tightly governed enterprise deployments to federated, privacy-sensitive ecosystems.
Why Agent Registries Matter Now
The web has historically relied on reactive, client-driven patterns where services wait for requests. Agents invert this pattern by acting proactively with persistent state, memory and the ability to orchestrate tasks or spawn other agents. As these behaviours scale into the billions of entities across heterogeneous platforms, the limits of the existing stack become clear. Name resolution, certificate revocation, state propagation and routing were not built for highly dynamic, self-directed software that forms short-lived collaborations and rotates endpoints.
Agent discovery now requires sub-second identity resolution, schema-validated capability descriptions and trustable metadata exchange that can cross organisational boundaries. A useful rubric groups evaluation into four dimensions. Security concerns the integrity of registry records and resistance to spoofing or poisoning, ideally through cryptographic signing. Authentication addresses publisher verification and namespace ownership, whether via platform credentials, domain proofs or decentralised identifiers. Scalability covers high lookup volumes, geo-distribution and caching that keeps latency low. Maintenance focuses on simplicity through schema-first designs, decoupled metadata hosting and minimal operational surface by avoiding executable code storage. These dimensions expose the trade-offs that separate centralised convenience from federated resilience.
Contrasting MCP, A2A, Entra Agent ID and NANDA
Different registry models illustrate distinct architectural stances. The MCP Registry centres on a metaregistry that publishes structured metadata via a versioned configuration managed through a command-line tool. Publisher identity is tied to platform-level authentication, and reverse-DNS namespaces require domain verification. The service stores metadata rather than code, indexes documents for discovery and enables downstream clients to poll, cache and serve results at scale. This design reduces attack surface by delegating code integrity to existing ecosystems and leans on caching and optional mirrors for load distribution.
Agent2Agent (A2A) takes a transport-agnostic approach that standardises agent interaction over JSON-RPC on secure HTTP. Discovery hinges on an AgentCard that declares capabilities and security schemes. Identity and credential handling occur through established headers and protocols, allowing compatibility with bearer tokens, OpenID Connect, API keys or mutual TLS. Task handling emphasises asynchronous, long-running exchanges, with streaming and push mechanisms reducing polling overhead. By keeping the wire protocol simple and schema-led, A2A supports extensibility while minimising bespoke components.
Microsoft Entra Agent ID introduces a managed directory for agent identities integrated with existing enterprise identity tooling. Agents created within supported platforms surface as managed applications, giving administrators visibility, lifecycle controls and access governance consistent with user and service identities. The emphasis is on lifecycle, policy and governance rather than introducing a new discovery wire protocol. Deeper analysis of security, authentication, scalability and maintainability aligns with the availability of operational detail as the service matures.
The NANDA Index targets decentralised, federated environments with a quilt-like architecture that separates static identifier resolution from dynamic metadata and routing. A minimal AgentAddr record provides a signed mapping from an agent identifier to metadata locations and routing endpoints. Richer metadata is distributed as AgentFacts documents using self-describing schemas and verifiable credentials, enabling privacy-preserving updates independent of the lean index. A dynamic resolution layer interprets metadata to support static, rotating or adaptive endpoints with short time-to-live intervals, enabling geo-aware routing, load balancing and resilience without frequent index writes. Cryptographic signatures, verifiable claims and privacy-preserving paths underpin trust and reduce exposure of access patterns.
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A comparative view shows how these designs optimise for different best-fit contexts. Centralised metaregistries streamline publication and discovery for toolable agents and client ecosystems. Protocol-standardised cards enable straightforward self-description and marketplace-style discovery. Managed enterprise directories embed agent identity into existing governance. Decentralised indices emphasise verifiable metadata, fast revocation and privacy paths suited to highly mobile or sensitive deployments. Schema weight, endpoint freshness strategies, and revocation mechanisms vary accordingly, reflecting the targeted operating assumptions.
From Static Manifests to Verifiable, Federated Trust
Registry architectures can be read as an evolution across three phases. Early mechanisms relied n static files published at well-known locations, suitable for manual consumption or tightly coupled runtimes. As needs grew, dynamic APIs and formally validated schemas enabled richer introspection and installability within client ecosystems. The current direction moves towards cryptographically verifiable metadata and federated trust, where signatures, verifiable credentials and time-bounded claims provide integrity and rapid revocation, and where indices serve as stable anchors rather than mutable sources of truth.
In the verifiable phase, separating identity anchors from dynamic capability data reduces write amplification and supports high-churn environments. Short-lived credentials and status lists improve revocation speed. Decentralised identifiers and issuer-anchored attestations allow provenance to travel with the metadata, enabling portable trust across domains. Privacy-preserving indirection and adaptive routing mitigate exposure of requester behaviour and improve resilience under variable load or adverse conditions. The result is an architecture that can scale while maintaining integrity, privacy and interoperability across diverse governance models.
This phase-wise perspective clarifies why there is no single universal registry pattern. Protocol-specific ecosystems benefit from purpose-built registries that align with existing authentication and distribution channels. Enterprise deployments prioritise lifecycle governance, policy and integration. Open and federated environments require cryptographic verification, portable identities and privacy-aware resolution. Interoperability remains a central challenge as these worlds converge. Cross-protocol discovery, unified namespace handling and portable agent identities will be necessary to support real-world compositions that bridge centralised and decentralised domains.
Agent registries are becoming core infrastructure as autonomous systems scale and diversify. Centralised metaregistries, protocol-standardised self-descriptions, managed enterprise directories and decentralised indices each address security, authentication, scalability and maintenance in different ways. The choice depends on operating context, governance requirements and tolerance for central points of control. A clear trend favours separating static identity anchors from dynamic, verifiable metadata with fast revocation and privacy-aware discovery. The design signals are consistent: prioritise cryptographic integrity, portable trust and operational simplicity, select architectures aligned with existing governance, and plan for interoperability across ecosystems that will increasingly need to work together.
Source: Cornell University
Image Credit: Gettyimages
