> ## Documentation Index
> Fetch the complete documentation index at: https://splinter.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom Rules

> Define your own BLOCK/WARN rules

Create custom rules that evaluate before each operation.

## Usage

```python theme={null}
from splinter.control import RulesEngine, Rule, RuleAction

engine = RulesEngine()

# Block when budget is low
engine.add_rule(Rule(
    rule_id="budget_guard",
    name="Budget Guard",
    description="Block when budget is low",
    condition=lambda ctx: ctx.get("remaining_budget", 0) < 1.0,
    action=RuleAction.BLOCK,
    message="Budget too low for this operation",
))

# Evaluate rules
engine.evaluate({"remaining_budget": 0.5})  # Raises RuleViolationError
```

## Rule Actions

| Action  | Description                  |
| ------- | ---------------------------- |
| `BLOCK` | Block the operation          |
| `WARN`  | Log warning, allow operation |
| `LOG`   | Just log, allow operation    |

## Rule Priority

```python theme={null}
from splinter.control import RulePriority

Rule(
    rule_id="critical_check",
    priority=RulePriority.CRITICAL,  # Evaluated first
    ...
)
```

| Priority   | Value |
| ---------- | ----- |
| `CRITICAL` | 100   |
| `HIGH`     | 75    |
| `MEDIUM`   | 50    |
| `LOW`      | 25    |

## Built-in Rules

```python theme={null}
from splinter.control.rules import (
    budget_rule,
    step_limit_rule,
    agent_blocked_rule,
    tool_blocked_rule,
    pattern_rule,
)

# Budget threshold
engine.add_rule(budget_rule(threshold=1.0, action=RuleAction.BLOCK))

# Block specific agent
engine.add_rule(agent_blocked_rule("bad_agent"))

# Block specific tool
engine.add_rule(tool_blocked_rule("dangerous_tool"))

# Pattern matching
engine.add_rule(pattern_rule(
    pattern=r"password|secret",
    field="user_input",
    action=RuleAction.BLOCK,
))
```

## Enable/Disable

```python theme={null}
engine.disable_rule("budget_guard")
engine.enable_rule("budget_guard")
```

## Match History

```python theme={null}
# Get all matches
matches = engine.get_matches()

# Filter by rule
matches = engine.get_matches(rule_id="budget_guard")

# Filter by action
matches = engine.get_matches(action=RuleAction.BLOCK)
```

## Error Handling

```python theme={null}
from splinter.control.rules import RuleViolationError

try:
    engine.evaluate(context)
except RuleViolationError as e:
    print(f"Rule '{e.rule_name}' violated: {e.message}")
```