Agent Object Protocol (AOP)

Status: Active specification repository Latest Release: v1.1.0 (release notes) Public API: Frozen at v1.0.0 (AEP-0009, V1_PUBLIC_API_CANDIDATE) Conformance: Levels 2-8 published; optional Level 9 integration is tracked by AEP-0011 Scope: Interoperability artifacts only (schemas + fixtures + CI gates; no reference runtime in this repo) License: Apache-2.0

Versioning note: Repository releases follow SemVer (v1.x.y). Manifest field aop_version currently targets pre-v1 payload generations (0.x) in the published schemas. Treat repository release tags and payload aop_version as separate version axes.

Agent Object Protocol (AOP) is an open standard effort for defining portable executable object contracts for AI agent ecosystems.

AOP emphasizes reproducible interoperability artifacts:

• JSON Schemas as machine-readable contracts
• Positive/negative fixtures as executable examples
• CI gates as adjudicable conformance checks

Quick Links

• Public API surface: V1_PUBLIC_API_CANDIDATE.md
• Conformance profile: CONFORMANCE.md
• Core schema families:
  • schemas/aop-object.schema.json
  • schemas/aop-policy.schema.json
  • schemas/aop-policy-decision.schema.json
  • schemas/aop-evidence.schema.json
  • schemas/profiles/*.schema.json
• Release milestones:
  • RELEASE_NOTES_v1.0.0.md
  • RELEASE_NOTES_v1.1.0.md

Paper Evidence

Artifact baseline used for the paper evidence chain:

• Code baseline: main@c9f94ee
• Evidence assets baseline: main@41242b1
• CI evidence run: 22717328360
• Figure S8: docs/paper-evidence/ci/S8_adversarial-gate-summary-ci.png
• S8 clean log excerpt: docs/paper-evidence/ci/ci_run_22717328360_job_65870183177.clean.log

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Motivation

Current agent stacks have transport and invocation standards, but often lack a stable, portable object contract layer for manifest shape, governance, policy decisions, and evidence binding.

AOP fills this gap by defining interoperable artifacts that can be validated independently of any specific runtime.

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Core Concepts

An AOP object manifest includes:

• aop_version
• id
• kind
• name
• description
• schema.inputs
• schema.outputs

Minimal object example (aligned with current schema shape):

{
  "aop_version": "0.9",
  "id": "urn:aop:tool:file-search:v1",
  "kind": "tool",
  "name": "file-search",
  "description": "Search files in a directory",
  "schema": {
    "inputs": {
      "type": "object",
      "properties": {
        "path": { "type": "string" },
        "query": { "type": "string" }
      },
      "required": ["path", "query"],
      "additionalProperties": false
    },
    "outputs": {
      "type": "object",
      "properties": {
        "results": {
          "type": "array",
          "items": { "type": "string" }
        }
      },
      "required": ["results"],
      "additionalProperties": false
    }
  }
}

---

Normative and Non-Normative Sources

For the v1 public API baseline, normative sources are:

• V1_PUBLIC_API_CANDIDATE.md
• schemas/aop-object.schema.json
• schemas/aop-policy.schema.json
• schemas/aop-policy-decision.schema.json
• schemas/aop-evidence.schema.json
• schemas/profiles/*.schema.json included in the v1 candidate surface
• CONFORMANCE.md levels and gate semantics

Non-normative but CI-validated interoperability artifacts include:

• schemas/aop-registry-record.schema.json
• schemas/aop-resolve-response.schema.json
• examples/** and examples/invalid/**

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Quick Start (Validation)

Compile all top-level schemas (Draft 2020-12):

for schema in schemas/*.schema.json; do
  ajv compile --spec=draft2020 -s "${schema}"
done

For fixture-level validation rules (including semantic gates, profile checks, and positive/negative expectations), use:

• CONFORMANCE.md
• .github/workflows/ci.yml

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Relationship to MCP

AOP is complementary to the Model Context Protocol (MCP):

• MCP focuses on tool transport and invocation channels.
• AOP focuses on object contracts and conformance artifacts.

MCP and AOP are designed to compose, not compete.

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Relationship to FAIR Digital Objects

AOP is inspired by FAIR Digital Object principles:

• persistent identifiers
• machine-readable metadata
• interoperability-first semantics

AOP applies these ideas to executable agent object contracts.

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Milestones and History

• v0.5 baseline release:
  • RELEASE_NOTES_v0.5.0.md
• v1.0 public API freeze:
  • RELEASE_NOTES_v1.0.0.md
  • aep/aep-0009-v1.0-freeze.md
• v1.1 DSSE optional profile:
  • RELEASE_NOTES_v1.1.0.md
  • aep/aep-0010-v1.1-dsse-optional-profile.md
• v1.2 in-toto DSSE compatibility (in progress):
  • aep/aep-0011-v1.2-in-toto-statement-compat.md

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Status

AOP is actively maintained as a specification repository.

Contributions are welcome through AEP proposals, schema updates, fixtures, and conformance-gate improvements.

Citation

Zhang, B. (2026). Agent Object Protocol: Protocol-by-Artifacts for Machine-Adjudicable AI Artifacts. Zenodo. https://doi.org/10.5281/zenodo.18876796