Block oversized file writes
Stops a 500 KB dump from bloating your repo
Blocks a single Write whose content exceeds ~500 KB — almost always an accidental dump, a generated blob, or a runaway paste that balloons the repo and the diff. Pure byte-length check, no file I/O, so it is effectively free.
What does the Block oversized file writes hook do?
Block oversized file writes is a Claude Code PreToolUse hook matching Write. It fires automatically at that lifecycle event — outside the model, so it can't be skipped or forgotten. Stops a 500 KB dump from bloating your repo.
As a PreToolUse hook it runs before the action completes, so it can block or adjust what Claude is about to do. Because it is a deterministic Node.js script, it executes on every matching event without relying on the model to remember — the guarantee that makes agentic workflows safe to automate.
Use cases
- Repo hygiene
- Reviewable diffs
- Catch accidental dumps
Tags
settings.json fragment
{
"hooks": {
"PreToolUse": [
{
"hooks": [
{
"command": "node $CLAUDE_PROJECT_DIR/.claude/hooks/block-huge-write.mjs",
"type": "command"
}
],
"matcher": "Write"
}
]
}
}Script · .claude/hooks/block-huge-write.mjs
#!/usr/bin/env node
// Bloque l'écriture d'un fichier anormalement volumineux (PreToolUse Write)
import { readFileSync } from 'fs';
import { fileURLToPath } from 'url';
// 500 Ko : au-delà, c'est presque toujours un dump, un blob généré ou un collage accidentel.
const MAX_BYTES = 500_000;
export function run(input, { maxBytes = MAX_BYTES } = {}) {
// Seul Write fournit le contenu complet ; Edit est un patch ciblé, on l'ignore.
if (input.tool_name && input.tool_name !== 'Write') return null;
const content = input.tool_input?.content;
if (typeof content !== 'string') return null;
const bytes = Buffer.byteLength(content, 'utf8');
if (bytes <= maxBytes) return null;
const filePath = input.tool_input?.file_path ?? 'le fichier';
const kb = Math.round(bytes / 1024);
return {
decision: 'block',
reason:
`Écriture de ${filePath} bloquée : ${kb} Ko (> ${Math.round(maxBytes / 1024)} Ko). ` +
'Un fichier de cette taille est généralement un dump ou un blob généré qui gonfle le repo et le diff. ' +
'Vérifiez l\'intention : générez-le à la volée, gitignorez-le, ou découpez-le.',
};
}
/* v8 ignore next 5 */
if (process.argv[1] === fileURLToPath(import.meta.url)) {
const input = JSON.parse(readFileSync(0, 'utf8'));
const result = run(input);
if (result) process.stdout.write(JSON.stringify(result));
}