AI Agent Tool Call Governance

Brane governs AI agent tool calls by wrapping each tool as a capability and running policy before the tool executes. If a policy denies the attempted tool call, Brane raises CapabilityDeniedError and the original function does not run. This is the right boundary for production agents because most agent risk comes from what tools do, not only from what the model says.

Tool Calls Are Capabilities

In Brane, a tool is one kind of Capability:

@runtime.capability(name="delete_user", type="tool", risk="critical")
def delete_user(user_id: str):
    ...

The capability metadata gives policies enough context to make governance decisions.

Example: Require Approval Signal For A Destructive Tool

@runtime.before_capability("delete_user")
def require_delete_approval(ctx):
    if not ctx.action.metadata.get("approved"):
        return Decision(
            type="deny",
            reason="delete_user requires an approval signal",
        )
    return Decision(type="allow")

The tool does not execute unless the policy allows it.

Example: Tenant Isolation

@runtime.before_capability("*")
def enforce_tenant_boundary(ctx):
    requested_tenant = ctx.arg("tenant_id", ctx.tenant_id)
    if requested_tenant != ctx.tenant_id:
        return Decision(type="deny", reason="Cross-tenant action blocked")
    return Decision(type="allow")

This pattern protects tools that accept tenant IDs, customer IDs, account IDs, or other scope-bearing arguments.

Tool Governance Checklist

For every production tool, define:

Capability name
Capability type
Risk level
Owner
Tenant or data namespace
Required scopes
Before-capability policies
After-capability policies for output checks

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AI Agent Tool Call Governance

Tool Calls Are Capabilities

Example: Require Approval Signal For A Destructive Tool

Example: Tenant Isolation

Tool Governance Checklist

​Tool Calls Are Capabilities

​Example: Require Approval Signal For A Destructive Tool

​Example: Tenant Isolation

​Tool Governance Checklist

​Related Pages

Tool Calls Are Capabilities

Example: Require Approval Signal For A Destructive Tool

Example: Tenant Isolation

Tool Governance Checklist

Related Pages