Policy-as-Code For AI Agents

Brane is policy-as-code for AI agents. Developers write normal Python functions that inspect an attempted agent action and return a structured decision such as allow or deny. The policy runs at runtime before the agent uses a capability, so the policy can block unsafe tool calls, database queries, model calls, MCP tools, memory writes, file access, and other actions.

What Policy-as-Code Means In Brane

A Brane policy is not a prompt. A Brane policy is application code:

from brane import Decision

@runtime.before_capability("refund_customer")
def refund_limit(ctx):
    amount = ctx.arg("amount_usd", 0)
    if amount > 100:
        return Decision(type="deny", reason="Refund exceeds $100 limit")
    return Decision(type="allow")

Because policies are Python functions, they can use your application context, tenant settings, environment, risk metadata, scopes, and audit rules.

Why Policy-as-Code Is Better Than Prompt Rules

Prompt rules are advisory. Policy code is enforceable.

Approach	What it can do	Limitation
Prompt instruction	Tell the model what behavior is expected	The model may ignore or misunderstand it
Output filter	Inspect final text	The action may already have happened
Brane policy	Intercept the attempted action	Requires registering capabilities

Brane policies run before the consequence occurs.

Policy Inputs

Every policy receives a PolicyContext. The context includes:

The capability being attempted
The input arguments
The agent identity
The principal identity
The tenant
The environment
The capability risk level
The output for after-capability policies

Policy Output

Every policy returns a Decision:

Decision(type="allow")
Decision(type="deny", reason="Only SELECT queries are allowed")

Today, allow and deny are implemented. Additional decision types such as approval_required, redact, transform_input, and transform_output are planned.

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Policy-as-Code For AI Agents

What Policy-as-Code Means In Brane

Why Policy-as-Code Is Better Than Prompt Rules

Policy Inputs

Policy Output

​What Policy-as-Code Means In Brane

​Why Policy-as-Code Is Better Than Prompt Rules

​Policy Inputs

​Policy Output

​Related Pages

What Policy-as-Code Means In Brane

Why Policy-as-Code Is Better Than Prompt Rules

Policy Inputs

Policy Output

Related Pages