# Custom condition

> Warn on edits that exceed a line-count threshold using a project-specific predicate.

The built-in conditions ([Tool](../../reference/conditions.md#captain_hook.Tool), [FilePath](../../reference/conditions.md#captain_hook.FilePath), [Content](../../reference/conditions.md#captain_hook.Content), [SourceEdits](../../reference/state-sessions.md#captain_hook.SourceEdits), …) cover the common cases, but you'll eventually want a predicate that depends on something specific to your project: a line-count threshold, a project-specific file shape, or a computed property of the event. Any frozen dataclass implementing `check(self, evt: BaseHookEvent) -> bool` satisfies the [CustomCondition](../../reference/conditions.md#captain_hook.CustomCondition) protocol and slots into `only_if=` / `skip_if=` alongside built-in conditions.

``` python
"""Warn on edits larger than a line-count threshold via a custom condition."""

from __future__ import annotations

from dataclasses import dataclass

from captain_hook import (
    Allow,
    BaseHookEvent,
    CustomCondition,
    Event,
    Input,
    Warn,
    nudge,
)


@dataclass(frozen=True)
class LargeEdit(CustomCondition):
    max_lines: int = 50

    def check(self, evt: BaseHookEvent) -> bool:
        return evt.content is not None and evt.content.count("\n") > self.max_lines


nudge(
    "Large edit detected -- consider splitting into smaller changes.",
    only_if=[LargeEdit(max_lines=10)],
    events=Event.PreToolUse,
    tests={
        Input(tool="Edit", content="\n".join(str(i) for i in range(20))): Warn(),
        Input(tool="Edit", content="one\ntwo\n"): Allow(),
    },
)
```


# What it catches

``` python
Input(tool="Edit", content="\n".join(str(i) for i in range(20)))  # 20-line edit clears the 10-line threshold
```


# What it allows

``` python
Input(tool="Edit", content="one\ntwo\n")  # small edit stays under the threshold
```

*The catch / allow split mirrors the hook inline `tests`, so it stays true as the hook evolves.*


# Run it yourself

``` bash
uvx capt-hook --hooks docs/examples test
```


# See also

- [Conditions](../../docs/reference/conditions.md)
- [Primitives](../../docs/guide/primitives.md)