claude warmer

Keep your Claude Code caches alive while you sleep, go for lunch, or touch grass. Periodically sends lightweight prompts to your sessions via claude --resume so that 1h TTL cache writes are refreshed.

Without warming, resuming a session older than 1 hour means a full cache write - $10 per M tokens for Opus 4.6. With warming, you pay $0.5 per M tokens for keep-alive instead. Cache reads and refreshes are 20x cheaper than 1h cache writes.

Usage is not recommended yet: As of Claude Code version 2.1.92, there is a bug where cross-process claude --resume result in non-deterministic plugin skill and tool definitions, which invalidates most of the cached prefix. The fix (an upcoming attachment system) exists behind a feature flag in Claude Code. Once enabled, cross-process cache hits should reach >90%.

Not affiliated with or endorsed by Anthropic.

Install

npx claude-warmer

Or install globally:

npm install -g claude-warmer
claude-warmer

Options:

• -i, --interval <minutes> - Warming interval (default: 55, just under the 1h cache TTL)
• --prompt <string> - Prompt to send (default: "Reply 'ok'")

How it works

1. Discovers all Claude Code sessions from ~/.claude/projects/
2. Shows a TUI with session status (warm/cold/live), cached tokens, and estimated costs
3. Select sessions to keep warm, press Enter to start
4. The warmer spawns claude --resume <id> in a PTY, sends the prompt, waits for a response, then exits
5. Sessions are refreshed every 30s to pick up new sessions and updated cache metrics

Keybindings

| Key | Action | |-----|--------| | Enter | Start/stop warming | | Space | Toggle session selection | | a | Select all live/warm sessions | | n | Deselect all | | i | Edit interval | | p | Edit prompt | | c | Copy session ID | | q | Quit |

Development

git clone https://github.com/ryanlyn/claude-warmer.git
cd claude-warmer
npm install
npm run dev

If node-pty fails with posix_spawnp on macOS Apple Silicon, run:

chmod +x node_modules/node-pty/prebuilds/darwin-arm64/spawn-helper

Tests

npm test          # unit tests (100% coverage required)
npm run check     # lint + format + coverage
npm run test:e2e  # E2E cache hit test (hits real API, slow)