AEP is an open API design specification for resource-oriented REST and gRPC APIs — a numbered set of design guidelines (resources, standard methods, pagination, filtering, long-running operations, errors and more) published as versioned, stable editions, with tooling that works with any API that conforms. It was forked in 2023 from Google’s API Improvement Proposals (AIP) by contributors who wanted organization-agnostic guidance formal enough to build tooling on. The first stable edition, aep-2026, was released in November 2025; aep-2028-preview accumulates the next. Content is CC BY 4.0, code samples Apache 2.0.
AEP
AEP turns API design guidance into a specification you can conform to. Each AEP is a numbered guideline — resource-oriented design, the standard methods (get, list, create, update, delete, apply), pagination, filtering, long-running operations, errors, idempotency, batch methods and more — and the set is published in versioned editions that tooling can target.
It descends directly from Google’s API Improvement Proposals, which open sourced Google’s internal API design practices. According to the project’s own history, contributors to aip.dev who wanted “a stronger formalization of the API design guidance itself” — a reference point independent of any one organization, and an official tooling ecosystem — forked it in 2023 and created aep.dev. Contributors cite experience at Google, Microsoft, Meta, Roblox, IBM and Databricks. (The governance document and history call the project API Enhancement Proposals; the current site header reads Application Enhancement Proposals.)
- Stable editions - AEP-300 defines edition-based versioning: stable editions named
for their year never change after publication, preview editions accumulate changes, patch versions only fix
typos or clarify, and editions are published every two years. aep-2026
was released on 22 November 2025;
aep-2028-previewis the next. - REST and gRPC - Guidance covers both HTTP/JSON APIs described with OpenAPI (AEP-101) and Protocol Buffers APIs, including HTTP and gRPC transcoding and field masks.
- Conformance unlocks clients - APIs that conform can use the project’s tooling without configuration: an
OpenAPI linter, a protobuf linter,
aepcto generate compliant APIs from a resource model, a CLI, a Terraform provider that configures itself at runtime, an API explorer UI, an MCP server and an end-to-end validator. - Multi-organization governance - AEP-6 places the project under a steering committee of at least five representatives from at least five organizations, with no more than a third from any one.
- Open content - Guidance is licensed CC BY 4.0 and code samples Apache 2.0.
