DocumentationPostCompact

Save compaction summary to log

Appends the compaction summary generated by Claude Code to a markdown log file inside the project. Provides a persistent record of what was summarized across context window resets, useful for long-running sessions and post-session review.

Use cases

Keep a human-readable history of every compaction event in the project
Review what Claude summarized at context boundaries for debugging or audit
Reconstruct the timeline of a long session from compaction summaries

Providers & tags

Claude Code

#compaction#logging#documentation#context

settings.json fragment

{
  "hooks": {
    "PostCompact": [
      {
        "hooks": [
          {
            "command": "node $CLAUDE_PROJECT_DIR/.claude/hooks/post-compact-save-summary.mjs",
            "type": "command"
          }
        ]
      }
    ]
  }
}

Script · .claude/hooks/post-compact-save-summary.mjs

#!/usr/bin/env node
// Journalise le résumé de compaction dans .claude/compaction-log.md (PostCompact)
import { readFileSync, appendFileSync, mkdirSync } from 'fs';
import { join, dirname } from 'path';
import { fileURLToPath } from 'url';

export function run(
  input,
  {
    append = appendFileSync,
    mkdir = mkdirSync,
    projectDir = process.env.CLAUDE_PROJECT_DIR ?? '.',
    now = () => new Date().toISOString(),
  } = {},
) {
  const summary = input.compact_summary ?? '';
  if (!summary.trim()) return null;

  const logPath = join(projectDir, '.claude', 'compaction-log.md');
  try { mkdir(dirname(logPath), { recursive: true }); } catch { /* exists */ }

  const entry = `\n## ${now()} (${input.trigger ?? 'auto'})\n${summary}\n`;
  append(logPath, entry);
  return entry;
}

/* v8 ignore next 4 */
if (process.argv[1] === fileURLToPath(import.meta.url)) {
  const input = JSON.parse(readFileSync(0, 'utf8'));
  run(input);
}