Policy Languages — CEL, Rego, Cedar

Audience

Policy authors and runtime maintainers comparing supported policy-language inputs with current enforcement behavior.

Outcome

After this page you should know what this surface is for, which source files own the behavior, which public route or adjacent page to use next, and which validation command to run before changing the claim.

Source Truth

• Public route: helm-ai-kernel/architecture/policy-languages
• Source document: helm-ai-kernel/docs/architecture/policy-languages.md
• Public manifest: helm-ai-kernel/docs/public-docs.manifest.json
• Source inventory: helm-ai-kernel/docs/source-inventory.manifest.json
• Validation: make docs-coverage, make docs-truth, and npm run coverage:inventory from docs-platform

Do not expand this page with unsupported product, SDK, deployment, compliance, or integration claims unless the inventory manifest points to code, schemas, tests, examples, or an owner doc that proves the claim.

helm-ai-kernel accepts policy sources written in three languages and routes them through one enforcement boundary. The kernel never branches on language at decision time; only the multi-language registry in core/pkg/policybundles/registry.go does, and only at compile/load.

CEL — historical baseline

Common Expression Language. Single expression returning a verdict envelope. Carried via the existing core/pkg/celcheck/ and core/pkg/policybundles/builtin.go pipeline.

• Inputs: request.action, request.principal.roles, request.context.
• Strengths: fastest evaluation, smallest dependency footprint, best fit for attribute-mostly rules.
• Weaknesses: limited control flow; nested ternaries get unwieldy.
• Example: examples/policies/cel/example.cel.

OPA / Rego — procurement standard

Rego via core/pkg/policybundles/rego/.

• Inputs: top-level input document.
• Strengths: rich set semantics, partial evaluation, mature ecosystem.
• Determinism guard: core/pkg/policybundles/rego/capabilities.json forbids http.send, time.now_ns, rand.intn, and crypto.x509.parse_certificates.
• Example: examples/policies/rego/example.rego.

Cedar — entity-shape model

Cedar via core/pkg/policybundles/cedar/.

• Inputs: principal/action/resource as EntityUID (Type::"id"); an optional entities document declares parent chains for the in operator.
• Strengths: explicit entity types, native role/group reasoning, AWS Verified Permissions interop.
• Example: examples/policies/cedar/example.cedar with companion entities at examples/policies/cedar/entities.json.

Side-by-side: same logical rule

Anyone may view; only admins may delete; default deny.

request.action == "view"
  ? {"verdict": "ALLOW"}
  : (request.action == "delete" && ("admin" in request.principal.roles)
       ? {"verdict": "ALLOW"}
       : {"verdict": "DENY"})

package helm.policy
import rego.v1

default decision := {"verdict": "DENY"}
decision := {"verdict": "ALLOW"} if { input.action == "view" }
decision := {"verdict": "ALLOW"} if {
  input.action == "delete"
  "admin" in input.principal.roles
}

permit(principal, action == Action::"view", resource);
permit(principal, action == Action::"delete", resource)
when { principal in Role::"admin" };

A regression test under tests/conformance/policy-langs/ (Workstream F1) will assert byte-identical decisions across all three on a 50-policy reference suite.

Edge-case behavior

Non-determinism rules (uniform)

Across all three languages, helm-ai-kernel enforces:

• No network I/O during evaluation.
• No random number generation.
• No system clock reads; the kernel injects now.
• No filesystem reads.
• No environment-variable reads.

Rego uses OPA's capabilities file. CEL uses the curated function set in core/pkg/celcheck/. Cedar's spec excludes these operations natively.

Choose your lane

Bundle manifests carry language: cel | rego | cedar. The kernel loads

• dispatches via core/pkg/policybundles/registry.go. The helm-ai-kernel bundle build subcommand auto-detects from file extension when --language is omitted.

See also

• core/pkg/policybundles/registry.go — language dispatch
• Conformance Profile v1 — required behavior across implementations
• Verification — verifying a built bundle's hash

Troubleshooting

Diagram

flowchart TD
    subgraph Ingestion["1. Ingestion & Context Plane"]
        cel["CEL"]
        rego["Rego"]
        cedar["Cedar"]
    end

    subgraph Evaluation["2. Evaluation & Policy Plane"]
        input["Canonical policy input"]
        decision["Normalized decision"]
    end

    subgraph Ledger["4. Tamper-Evident Ledger Plane"]
        receipt["Signed receipt"]
    end

    %% Operational Flow Edges
    input --> cel
    input --> rego
    input --> cedar
    cel --> decision
    rego --> decision
    cedar --> decision
    decision --> receipt

    %% Premium Styling Rules
    style input fill:#2d3748,stroke:#4a5568,stroke-width:2px,color:#fff
    style decision fill:#2d3748,stroke:#4a5568,stroke-width:2px,color:#fff
    style receipt fill:#2f855a,stroke:#276749,stroke-width:2px,color:#fff

flowchart TD
    subgraph Ingestion["1. Ingestion & Context Plane"]
        cel["CEL"]
        rego["Rego"]
        cedar["Cedar"]
    end

    subgraph Evaluation["2. Evaluation & Policy Plane"]
        input["Canonical policy input"]
        decision["Normalized decision"]
    end

    subgraph Ledger["4. Tamper-Evident Ledger Plane"]
        receipt["Signed receipt"]
    end

    %% Operational Flow Edges
    input --> cel
    input --> rego
    input --> cedar
    cel --> decision
    rego --> decision
    cedar --> decision
    decision --> receipt

    %% Premium Styling Rules
    style input fill:#2d3748,stroke:#4a5568,stroke-width:2px,color:#fff
    style decision fill:#2d3748,stroke:#4a5568,stroke-width:2px,color:#fff
    style receipt fill:#2f855a,stroke:#276749,stroke-width:2px,color:#fff