veto 0.9.0

A guardrail system that intercepts and validates AI agent tool calls

Veto

A guardrail system for AI agent tool calls. Veto intercepts and validates tool calls made by AI models before execution.

How It Works

1. Initialize Veto.
2. Wrap your tools using veto.wrap().
3. Pass the wrapped tools to your AI agent/model.

When the AI model calls a tool, Veto automatically:

1. Intercepts the call.
2. Validates arguments against your rules (via YAML & LLM).
3. Blocks or Allows execution based on the result.

The AI model remains unaware of the guardrail - the tool interface is preserved.

Installation

pip install veto

For a complete bank transfer escalation example, see the HITL guide.

For LLM provider support:

pip install veto[openai]      # OpenAI support
pip install veto[anthropic]   # Anthropic support
pip install veto[gemini]      # Google Gemini support
pip install veto[all]         # All providers

Quick Start

1. Initialize Veto

Run the CLI to create configuration:

veto init

This creates a veto/ directory with veto.config.yaml and default rules.

2. Wrap Your Tools

from veto import Veto

# 1. Define your tools normally
my_tools = [
    {"name": "my_tool", "handler": my_handler, ...},
    # ...
]

# 2. Initialize Veto
veto = await Veto.init()

# 3. Wrap tools (Validation logic is injected)
wrapped_tools = veto.wrap(my_tools)

# 4. Pass to your Agent/LLM
agent = create_agent(
    tools=wrapped_tools,
    # ...
)

3. Configure Rules

Edit veto/rules/financial.yaml (example):

rules:
  - id: limit-transfers
    name: Limit large transfers
    action: block
    tools:
      - transfer_funds
    conditions:
      - field: arguments.amount
        operator: greater_than
        value: 1000

Configuration

veto.config.yaml

version: "1.0"

# Operating mode
mode: "strict" # "strict" blocks calls, "log" only logs them

# Validation Backend
validation:
  mode: "custom" # "api" or "custom"

# Custom Provider (if mode is custom)
custom:
  provider: "gemini" # or openai, anthropic
  model: "gemini-3-flash-preview"

# Logging
logging:
  level: "info"

# Rules
rules:
  directory: "./rules"
  recursive: true

API Reference

Veto.init(options?)

Initialize Veto. Loads configuration from ./veto by default.

veto = await Veto.init()

veto.wrap(tools)

Wraps an array of tools. The returned tools have Veto validation injected into their execution handler.

wrapped_tools = veto.wrap(my_tools)

veto.wrap_tool(tool)

Wraps a single tool instance.

safe_tool = veto.wrap_tool(my_tool)

veto.get_history_stats()

Returns statistics about allowed vs blocked calls.

stats = veto.get_history_stats()
print(stats)
# {"total_calls": 5, "allowed_calls": 4, "denied_calls": 1, ...}

veto.clear_history()

Resets the history statistics.

veto.clear_history()

veto.export_decisions(format)

Exports decision history as JSON or CSV.

json_audit = veto.export_decisions("json")
csv_audit = veto.export_decisions("csv")

CLI Commands

Command	Description
veto init	Initialize Veto in current directory
veto version	Show version

License

MIT