# Compaction Strategies > Implement hook-based history compaction in fast-agent (rolling window, context threshold truncation, tool-result clearing, summary prompt compaction). Use when adding or extending compaction hooks and wiring them into agent cards. Use when this capability is needed. - Skill: `tomevault-io/compaction-strategies` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/compaction-strategies` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/compaction-strategies/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/compaction-strategies --- # Compaction strategies (hooks) Implement and wire compaction hooks via `after_turn_complete`. ## Quick start - Copy `scripts/compaction_hooks.py` into your project hooks module. - Pick a strategy and wire it via `tool_hooks.after_turn_complete`. - Tune defaults in the hook or wrap it in a custom function (hook specs do not accept params). ### Agent card wiring ```yaml tool_hooks: after_turn_complete: hooks.py:rolling_window ``` ## Strategy menu - **Rolling window** → `rolling_window` - **Truncate over threshold** → `truncate_over_threshold` - **Clear results (soft)** → `clear_results_soft` - **Clear results (hard)** → `clear_results_hard` - **Compaction prompt** → `compaction_prompt` See [references/compaction.md](references/compaction.md) for the design summary. ## Hook requirements - Guard with `if not ctx.is_turn_complete: return`. - Use `ctx.usage` when available to read context usage. - Use `ctx.load_message_history(...)` to replace history. - Use `show_hook_message(...)` to display a compaction notice. ## Testing Run a hook against saved history: ```bash python scripts/hook_smoke_test.py \ --hook path/to/hooks.py:rolling_window \ --history ./history.json \ --hook-type after_turn_complete \ --output ./history-modified.json ``` --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/fast-agent-ai) — claim your Tome and manage your conversions.