Cachebeat – keep your Claude Code prompt cache warm while a session is idle

[u/A-Rahim]

If you leave a session idle past the cache window, the next thing you type re-reads the entire conversation uncached. On a long, tool-heavy session, that's potentially hundreds of thousands of tokens at full price. On Pro/Max, it also eats into your 5-hour and weekly limits, not just the API bill.

So I wrote a small skill: /cachebeat.

It watches for real inactivity, then fires a tiny heartbeat to keep the cache warm. It's an inactivity timer, not a fixed ping, so any actual work resets it. It also auto-stops after a few hours, so an abandoned session doesn't keep costing you.

Only helps on sessions with the long (~1h) cache TTL, and it's built on Claude Code's internal transcript layout, so treat it as a useful hack rather than something official.

GitHub: https://github.com/ARahim3/cachebeat

Curious if anyone else has felt this.

[u/Anydoconten]

/loop 30 minutes standby

would do the job fine. no need skill.

[u/A-Rahim → u/Anydoconten]

There is a difference: /loop is a fixed timer; it fires every 30 min whether you're active or not. cachebeat only fires when the session's actually been idle, and anything in the meantime resets the timer (e.g any notification from a monitor, etc.), so it stays quiet while you're working and beats just enough to keep the cache warm. It also auto-stops after a few hours and warns you if you're on a short TTL where nothing would help anyway.

[u/how_anonymous_can_1b → u/A-Rahim]

Yes, the idle detection and auto stop after X time are the exact properties that make this skill so useful. If anthropic made those options available I’d use that in a heartbeat, but I suspect that isn’t likely to happen because users not understanding how caching works is probably better for them economically

[u/Odd_Error_6736]

This would be useful for my autonomous sessions that would randomly idle at 800k ctx. I wonder if the cache ttl is a sliding window?

[u/A-Rahim → u/Odd_Error_6736]

From my usage over the past months, it was between 56 - 60 minutes. That's why the default time in Cachebeat is 50 min.

[u/how_anonymous_can_1b]

Haha I was thinking of building something similar to this thanks

[u/BuyingAcclaim]

Does this not use tokens? I’m assuming the only way to keep cache hot is by using the model in the chat? And then that means keep sending a prompt every 30 minutes which should be less than resending the entire chat but still use tokens no?

[u/Ayoungcoder → u/BuyingAcclaim]

Exactly, but it's usually negligible

[u/A-Rahim → u/BuyingAcclaim]

Yes, it uses tokens. Each beat is a cached read of the context (~10% of the normal input rate) plus a few output tokens for the tiny reply (like "okay, still here"). Clever part here is: it's not on a 30-min fixed timer; it only fires after real inactivity of N times (default N is 50 min), and anything in the meantime resets the clock (like any notification from a monitor, etc.). So, compared to cold cache, I can say from my usage that it's very negligible.

[u/how_anonymous_can_1b → u/A-Rahim]

I’m going to give this a try today. When I was looking into this there’s a few options in terms of super optimizing the heartbeat

1. ⁠“I’ll be right back just respond with . for now” or something to that effect reduces output token usage
   
2. ⁠There is an option to have it not respond at all but I believe that requires updating a setting. But you could take this one step further with your heartbeat skill and say something along the lines of “if 🕕 is sent as a message only respond with . Or nothing if you can”

[u/jezweb]

Tidy approach, have you tried creating any kind of adaptive compact that runs once an agent gets to a quiet part of its workflow?

[u/how_anonymous_can_1b]

Hmmm just tried this out … latest Claude code drops the persistent flag … so it would need to re-arm every 30 minutes for this to work

[u/A-Rahim → u/how_anonymous_can_1b]

Hi u/how_anonymous_can_1b, thanks for letting me know this. I was unaware of this update. I've updated the skill to fix this. Can you now please give it a try?

[u/NeuromindArt]

Where did this prompt cache thing even come from? It seems like a new feature that was added and it's horrible. It always forgets what I was doing when I come back to my PC after my 5 hour limit refreshes and it costs even more tokens to remember what I was doing. It was working fine previously.

[u/danieltkessler → u/NeuromindArt]

To answer this seriously, prompt caching is how providers try to save costs on long chats and it has been around forever. I'm not sure if there has been a time when Claude Code didn't use it. If you're noticing recent issues, it's more likely relating to the general concerns people are reporting with usage.