initguard 2026.3.3

Embedded ABAC policy engine for AI agents

initguard

Embedded ABAC policy engine for AI agents.

Write authorization policies in YAML with CEL conditions, evaluate them in-process. No sidecar, no HTTP, no external service. Policies use when/unless clauses for readable rules and return structured Decision objects with human-readable reasons and advice.

Install

pip install initguard

Quick start

Create a policy file:

# policies/tool_policy.yaml
apiVersion: initguard/v1
kind: ResourcePolicy
resource: tool
rules:
  - actions: ["execute"]
    effect: allow
    roles: ["agent"]
    when: request.resource.attr.tool_type in ["http", "search"]

  - actions: ["execute"]
    effect: deny
    roles: ["agent"]
    when: request.resource.attr.tool_type == "shell"
    unless: request.principal.attr.tags.exists(t, t == "trusted")
    advice: "Shell tools require the 'trusted' tag."

Load and evaluate:

from initguard import PolicyEngine, Principal, load_policies

engine = PolicyEngine(load_policies("./policies"))

agent = Principal(
    id="agent:helper",
    roles=["agent"],
    attrs={"tags": ["basic"]},
)

decision = engine.check(agent, "tool", "execute", resource_attrs={"tool_type": "shell"})

print(decision.allowed)  # False
print(decision.reason)   # "denied by tool_policy.yaml:rules[1]"
print(decision.advice)   # "Shell tools require the 'trusted' tag."

Policy format

Three document kinds, all in YAML.

Schema (optional)

Lint your policies against known attribute names. Catches typos at load time.

apiVersion: initguard/v1
kind: Schema
principals:
  agent:
    attrs:
      team: string
      tags: list
resources:
  tool:
    attrs:
      tool_type: string
    actions: [execute]

DerivedRoles

Conditional role elevation using CEL. A definition matches when when is true and unless is false (or absent). Names must be globally unique.

apiVersion: initguard/v1
kind: DerivedRoles
name: agent_roles
definitions:
  - name: trusted_agent
    parentRoles: ["agent"]
    when: request.principal.attr.tags.exists(t, t == "trusted")

  - name: same_team
    parentRoles: ["agent"]
    when: request.principal.attr.team != ""
    unless: request.principal.attr.team != request.resource.attr.team

ResourcePolicy

Allow/deny rules for a resource kind. Deny always wins over allow. Every rule must declare at least one of roles or derivedRoles.

apiVersion: initguard/v1
kind: ResourcePolicy
resource: tool
importDerivedRoles: [agent_roles]
rules:
  - actions: ["execute"]
    effect: allow
    derivedRoles: ["trusted_agent"]

  - actions: ["execute"]
    effect: deny
    roles: ["agent"]
    when: request.resource.attr.tool_type in ["shell", "python"]
    unless: request.principal.attr.tags.exists(t, t == "trusted")
    advice: "Requires the 'trusted' tag."

Derived roles are scoped to imports -- a ResourcePolicy only sees roles from the sets it explicitly imports, preventing privilege leakage across policy domains.

API

load_policies(policy_dir) -> PolicySet

Load all *.yaml / *.yml files from a directory. Files are loaded in sorted order for deterministic precedence. All CEL expressions are compiled at load time. Raises PolicyLoadError on invalid YAML, bad CEL syntax, duplicate role names, or broken references.

PolicyEngine(policy_set)

engine = PolicyEngine(policy_set)

engine.check(principal, resource_kind, action, resource_id="*", resource_attrs=None) -> Decision

Evaluate policies and return a Decision. Also available as check_async for async contexts.

engine.info() -> EngineInfo

Returns loaded policy summary: resource kinds, derived role sets, policy/rule counts, schema presence.

Decision

Field	Type	Description
allowed	bool	Whether the action is permitted
reason	str	Human-readable explanation, always populated
matched_rule	str	Stable rule identifier, e.g. "tool_policy.yaml:rules[1]"
advice	str	From the rule's advice field, or empty

Principal

Field	Type	Description
id	str	Identity string, e.g. "agent:code-reviewer"
roles	list[str]	Role list, e.g. ["agent", "team:platform"]
attrs	dict[str, Any]	Attributes for CEL conditions

CEL expressions

Conditions use Google Common Expression Language. Supported patterns:

# List membership
request.resource.attr.tool_type in ["shell", "python"]

# Existential quantifier
request.principal.attr.tags.exists(t, t == "trusted")

# Attribute equality
request.principal.attr.team == request.resource.attr.team

# Boolean operators
!request.principal.attr.tags.exists(t, t == "admin") && request.resource.attr.tool_type == "shell"

Missing attributes in CEL expressions evaluate to false (condition not met), not an error.

Development

uv sync --all-extras
uv run pytest tests/ -v
uv run ruff check . && uv run ruff format --check .

License

MIT OR Apache-2.0