OpenRPC

Expanded Definition

OpenRPC is an interface description specification for JSON-RPC services that makes methods, parameters, result shapes, and shared types readable by machines as well as humans. For security teams, that matters because a service description can be used to generate clients, validate requests, build test cases, and map attack surface more precisely than ad hoc documentation.

OpenRPC is not the transport protocol itself and it is not an authentication standard. It sits one layer above the API implementation, describing how the RPC surface is expected to look so tooling can interact with it consistently. In practice, that can help defenders inventory methods, identify exposed operations, and verify whether security controls are applied uniformly across an RPC surface. The most relevant governance lens is the NIST Cybersecurity Framework 2.0, because OpenRPC supports asset visibility and control validation rather than replacing them.

Definitions are fairly stable in the developer tooling community, but usage in the industry is still evolving around whether OpenRPC documents should be treated as internal design assets, security artifacts, or external contracts. The most common misapplication is assuming that an OpenRPC file is itself a control, which occurs when teams confuse description coverage with actual authentication, authorisation, and input validation at runtime.

Examples and Use Cases

Implementing OpenRPC rigorously often introduces documentation maintenance overhead, requiring organisations to weigh better automation and testability against the cost of keeping the spec aligned with the live service.

• A security scanner ingests an OpenRPC document to enumerate callable methods and focus tests on high-risk operations such as administrative or account-changing actions.
• A development team generates integration tests from the spec so that parameter validation can be checked consistently before deployment.
• An internal platform team uses the document to compare intended RPC methods against what is actually exposed in production, helping detect shadow endpoints or undocumented functions.
• A red team references the method catalog to build targeted payloads for each input type instead of relying on broad, low-signal fuzzing.
• A governance team reviews the specification alongside the service owner’s access model to confirm that sensitive methods are not described as publicly callable when they should require stronger controls.

For teams building repeatable API assurance workflows, OpenRPC is most useful when paired with explicit control expectations and runtime telemetry. The specification does not decide who may call a method, but it gives defenders a shared source of truth for testing that decision. Standards guidance for asset and control mapping in NIST Cybersecurity Framework 2.0 helps place the spec in a broader assurance process.

Why It Matters for Security Teams

Security teams need to understand OpenRPC because machine readable service descriptions make both defence and misuse faster. When the specification is accurate, it supports discovery, regression testing, and policy checks. When it is stale or incomplete, attackers and testers alike can waste time on the wrong methods while the real exposure remains invisible. That is why OpenRPC is best treated as part of the secure software supply chain for API-like services, not as a simple developer convenience.

The identity connection matters when JSON-RPC methods perform privileged actions, handle tokens, or mediate access to Non-Human Identity workflows. In those cases, the spec can reveal which operations should require stronger authentication, scoped credentials, or tighter authorisation checks. It can also help teams review whether automation identities are being granted broader RPC access than they need. Guidance from the NIST Cybersecurity Framework 2.0 remains relevant because the core question is still visibility, protection, and validation of the service surface.

Organisations typically encounter the risk only after an undocumented method is abused or a test tool causes unintended production impact, at which point OpenRPC becomes operationally unavoidable to address.