SLOPSHOPPER

cache-clock

Shows how long the prompt cache stays warm as a countdown above the prompt, with an optional keep-warm mode.

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v0.1.0MITupdated 2026-10-26leowei31/cache-clock-mod/cache-clock
A shopper browsing a rack in a slop shop
Preview · a replayed session in a sandbox
claude · ~/work/app · cache-clock
› fix the failing auth test and add an audit log call ⏺ Read(src/auth.ts) ⎿ Read 6 lines ⏺ Update(src/auth.ts) ⎿ Added 2 lines, removed 1 line ⏺ Bash(bun test) ⎿ 3 pass, 1 fail ● Done. refresh now rejects expired claims and logs an audit event. ✻ Worked for 42s · done 4:20 PM › /keepwarm ⎿ cache-clock: Keep-warm on. ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── › ? for shortcuts
README

cache-clock

A Claude Code mod that shows how long your prompt cache stays warm, as a countdown above the prompt. It also has an optional keep-warm mode that refreshes the cache before it expires.

Why

Claude Code resends your whole conversation on every request. While the prompt cache is warm, the API serves most of it from cache at a fraction of the cost and latency. Once the cache expires, your next prompt pays for the whole context again. The mod shows how much time is left, so you know whether to reply now or accept a cold start.

What you see

Above the prompt:

cache warm 4:32 ████████░░░░  5m API   [Keep warm: off]
  • The countdown restarts whenever a request reads or writes the cache.
  • The bar turns green, then yellow, then red as time runs out.
  • When the cache has expired it says cache cold, because the next prompt re-bills your whole context.
  • The button turns keep-warm on and off. /keepwarm on and /keepwarm off do the same.

Subscription and API lifetimes

The cache lives for a different time depending on how you pay.

  • On a Claude subscription the mod assumes an hour.
  • With an API key it assumes five minutes.
  • The mod tells them apart by whether the session reports subscription rate limits.

The setting ttl overrides this with 5m or 1h. If you set ENABLE_PROMPT_CACHING_1H in your environment, auto uses one hour. If you set FORCE_PROMPT_CACHING_5M, auto uses five minutes. Check your own setup if the lifetime shown looks wrong, and set ttl explicitly.

Keep warm

When keep-warm is on, the mod sends one tiny request shortly before the cache expires. That request reads your cached context, which restarts the lifetime.

It is not free. Each request is a cache read of your whole context, billed at the cache-read rate, and on a subscription it counts against your usage limits. So it has guards:

  • It only sends while the cache is still warm, so it never pays to rebuild a cold cache.
  • It never sends while a turn is running.
  • It stops after maxPings requests in a row with no activity from you. The default is 6.
  • It stops if a request does not hit the cache.
  • Your next prompt resets the count.

Install

/plugin install cache-clock --marketplace leowei31/cache-clock-mod

Then start a new session.

Settings

SettingDefaultMeaning
ttlautoauto, 5m or 1h
keepWarmoffStart each session with keep-warm on
marginSeconds60How long before expiry the request is sent
maxPings6Most keep-warm requests in a row

Limits

  • The countdown is an estimate from the last request that touched the cache, not a reading from the server.
  • A different model or a /clear starts a new cache, and the countdown restarts with the next request.
  • It needs a Claude Code build that supports mods.

Development

Run claude plugin test ./cache-clock to run the tests. Run claude plugin validate ./cache-clock to validate the manifest.

Source 2 files
hooks/register.tsx 222 lines
1import { atom, read, update } from 'claude-code'
2import type { Register } from 'claude-code'
3
4import type { Plan } from '../types'
5
6const MINUTE = 60_000
7const TTL_5M = 5 * MINUTE
8const TTL_1H = 60 * MINUTE
9const BAR_WIDTH = 12
10const PING_PROMPT = 'Reply with a single period and nothing else.'
11
12const lastTouch = atom({ plugin: 'cache-clock', key: 'lastTouch' } as const, 0)
13const ttlMs = atom({ plugin: 'cache-clock', key: 'ttlMs' } as const, TTL_5M)
14const plan = atom({ plugin: 'cache-clock', key: 'plan' } as const, 'api' as Plan)
15const isKeepWarm = atom({ plugin: 'cache-clock', key: 'isKeepWarm' } as const, false)
16const pings = atom({ plugin: 'cache-clock', key: 'pings' } as const, 0)
17const note = atom({ plugin: 'cache-clock', key: 'note' } as const, '')
18const tick = atom({ plugin: 'cache-clock', key: 'tick' } as const, 0)
19
20// auto: a subscription caches for an hour, an API key for five minutes, unless the environment says otherwise.
21const resolveTtl = (mode: string, force1h: boolean, force5m: boolean, isSubscription: boolean) => {
22  if (mode === '5m') {
23    return TTL_5M
24  }
25
26  if (mode === '1h') {
27    return TTL_1H
28  }
29
30  if (force5m) {
31    return TTL_5M
32  }
33
34  return force1h || isSubscription ? TTL_1H : TTL_5M
35}
36
37const clock = (ms: number) => {
38  const total = Math.max(0, Math.ceil(ms / 1000))
39  const hours = Math.floor(total / 3600)
40  const minutes = Math.floor((total % 3600) / 60)
41  const rest = String(total % 60).padStart(2, '0')
42
43  return hours > 0 ? `${hours}:${String(minutes).padStart(2, '0')}:${rest}` : `${minutes}:${rest}`
44}
45
46const bar = (fraction: number) => {
47  const filled = Math.round(Math.min(1, Math.max(0, fraction)) * BAR_WIDTH)
48
49  return '█'.repeat(filled) + '░'.repeat(BAR_WIDTH - filled)
50}
51
52const ttlLabel = (ms: number) => (ms >= TTL_1H ? '1h' : '5m')
53
54export const register: Register = (on, options) => {
55  const mode = String(options.ttl ?? 'auto')
56  const margin = Math.max(5, Number(options.marginSeconds ?? 60)) * 1000
57  const maxPings = Math.max(1, Number(options.maxPings ?? 6))
58  let isBusy = false
59  let isPinging = false
60
61  on('session.start', async ($, e, next) => {
62    await $.command.register({
63      name: 'keepwarm',
64      description: 'Turn keep-warm on or off for the prompt cache',
65      argumentHint: '[on | off]',
66    })
67    await update($, isKeepWarm, () => options.keepWarm === true)
68
69    $.clock.every(1000, async () => {
70      const now = await $.clock.now()
71      const touched = await read($, lastTouch)
72
73      if (touched === 0) {
74        return
75      }
76
77      const ttl = await read($, ttlMs)
78      const left = touched + ttl - now
79
80      if (left > -2000) {
81        await update($, tick, n => n + 1)
82      }
83
84      const wantsPing = (await read($, isKeepWarm)) && !isBusy && !isPinging
85      const count = await read($, pings)
86
87      if (!wantsPing || left <= 0 || left > margin) {
88        return
89      }
90
91      if (count >= maxPings) {
92        await update($, isKeepWarm, () => false)
93        await update($, note, () => `keep-warm stopped after ${maxPings} requests`)
94
95        return
96      }
97
98      isPinging = true
99      const reply = await $.model.fork({ prompt: PING_PROMPT })
100      isPinging = false
101
102      if (reply.isAnswered && reply.usage.cache_read_input_tokens > 0) {
103        const done = await $.clock.now()
104        await update($, lastTouch, () => done)
105        await update($, pings, n => n + 1)
106        await update($, note, () => '')
107
108        return
109      }
110
111      await update($, isKeepWarm, () => false)
112      await update($, note, () => 'keep-warm stopped: the request did not hit the cache')
113    })
114
115    return next(e)
116  })
117
118  on('command.run', { command: 'keepwarm' }, async ($, e) => {
119    const arg = e.args.trim()
120    const isOn = arg === 'on' ? true : arg === 'off' ? false : !(await read($, isKeepWarm))
121    await update($, isKeepWarm, () => isOn)
122    await update($, pings, () => 0)
123    await update($, note, () => '')
124
125    return { text: isOn ? 'Keep-warm on.' : 'Keep-warm off.' }
126  })
127
128  on('turn.start', async ($, e, next) => {
129    if (e.agentId === undefined) {
130      isBusy = true
131    }
132
133    return next(e)
134  })
135
136  on('turn.complete', async ($, e, next) => {
137    if (e.agentId === undefined) {
138      isBusy = false
139    }
140
141    return next(e)
142  })
143
144  // Every main-thread request that reads or writes the cache restarts its lifetime.
145  on('turn.step', async function* ($, e, next) {
146    const out = yield* next(e)
147    const usage = out.usage
148
149    if (e.agentId === undefined && usage && (usage.cache_read_input_tokens > 0 || usage.cache_creation_input_tokens > 0)) {
150      const now = await $.clock.now()
151      const limits = await $.session.usage()
152      const isSubscription = limits.rateLimits.length > 0
153      const force1h = (await $.env.get('ENABLE_PROMPT_CACHING_1H')) !== undefined
154      const force5m = (await $.env.get('FORCE_PROMPT_CACHING_5M')) !== undefined
155
156      await update($, lastTouch, () => now)
157      await update($, ttlMs, () => resolveTtl(mode, force1h, force5m, isSubscription))
158      await update($, plan, () => (isSubscription ? 'subscription' : 'api'))
159      await update($, pings, () => 0)
160      await update($, note, () => '')
161    }
162
163    return out
164  })
165
166  on('ui.render', { component: 'AbovePrompt' }, async ($, e, next) => {
167    const touched = await read($, lastTouch)
168
169    if (e.props.hasSurvey || touched === 0) {
170      return next(e)
171    }
172
173    await read($, tick)
174    const { Box, Button, Text } = $.ui.resolve(e)
175    const now = await $.clock.now()
176    const ttl = await read($, ttlMs)
177    const left = touched + ttl - now
178    const kind = await read($, plan)
179    const warm = await read($, isKeepWarm)
180    const count = await read($, pings)
181    const message = await read($, note)
182    const toggle = (
183      <Button
184        key="keepwarm"
185        label={warm ? 'Keep warm: on' : 'Keep warm: off'}
186        onPress={() => {
187          void update($, isKeepWarm, () => !warm)
188          void update($, pings, () => 0)
189          void update($, note, () => '')
190        }}
191      />
192    )
193
194    if (left <= 0) {
195      return (
196        <Box gap={1}>
197          <Text color="red">cache cold</Text>
198          <Text dimColor>the next prompt re-bills your whole context</Text>
199          {toggle}
200        </Box>
201      )
202    }
203
204    const fraction = left / ttl
205    const color = fraction > 0.5 ? 'green' : fraction > 0.2 ? 'yellow' : 'red'
206
207    return (
208      <Box gap={1}>
209        <Text color={color}>
210          cache warm {clock(left)} {bar(fraction)}
211        </Text>
212        <Text dimColor>
213          {ttlLabel(ttl)} {kind === 'subscription' ? 'subscription' : 'API'}
214          {warm ? ` pings ${count}/${maxPings}` : ''}
215        </Text>
216        {message !== '' && <Text color="yellow">{message}</Text>}
217        {toggle}
218      </Box>
219    )
220  })
221}
222
types/index.d.ts 16 lines
1export type Plan = 'subscription' | 'api'
2
3declare module 'claude-code' {
4  interface PluginState {
5    'cache-clock': {
6      lastTouch: number
7      ttlMs: number
8      plan: Plan
9      isKeepWarm: boolean
10      pings: number
11      note: string
12      tick: number
13    }
14  }
15}
16