Concept
Caching rewards putting the unchanging part first.
A cache hit requires an identical prefix. One early edit invalidates everything after it.
Concept
Prompt Caching
Learn how prompt caching works, how to structure prompts to hit the cache, and what it saves. Free, one sitting.
Start Quick LessonFree to explore · ~3 minutes
Why this matters
Long system prompts, tool definitions and retrieved documents repeat on nearly every request. Caching them can cut cost dramatically and reduce latency at the same time — but only if the stable content sits at the front of the prompt, which is a structural decision most teams get wrong by default.
What you'll cover
What Caching Does
- The repeated preamble problem
- How prefix caching works
- What it saves
- Cache lifetime
- Provider differences
Structuring for Cache Hits
- Most stable content first
- Where tool definitions belong
- Retrieved documents
- The user turn goes last
- Restructuring an existing prompt
What Breaks the Cache
- Timestamps and dynamic values
- Per-user personalisation
- Reordering between requests
- Prompt edits and deployments
- Finding what broke it
Measuring Hit Rate
- What to measure
- Instrumenting your calls
- Reading the savings
- Alerting on a drop
- Setting a target
Caching in Real Systems
- Caching with agents
- Caching with RAG
- Multi-tenant considerations
- Combining with other levers
- A worked example
What you'll understand
- Explain what caching does to cost and latency
- Order a prompt so stable content is cacheable
- Measure your real cache hit rate
- Avoid changes that silently invalidate the cache
A look inside
Three moments from this Quick Lesson
The real thing — not a mockup of it.
How it fits
[Stable system + tools] → [Retrieved] → [User turn]
Most stable to least stable, left to right. That ordering is the whole technique.
Apply
What breaks a cache hit?
A longer user message at the end
A timestamp injected at the start of the system prompt
A different temperature
How it works
01
Understand the concept
A plain-language walkthrough of the idea itself, no prior context assumed.
02
See it in practice
A simple diagram or example showing how it actually fits together.
03
Apply what you learned
One quick check that you can recognise it, not just recall it.
Useful for
DevelopersAI engineersEngineering managersFounders
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Frequently asked
How much can caching actually save?+
On apps with a large fixed preamble, it commonly removes most of the input cost, since cached tokens are billed at a steep discount.
What will I learn?+
How prompt caching works, how to structure prompts to hit it consistently, and how to verify the savings.
Is this Quick Lesson free?+
Yes. Quick Lessons are free, short, and do not require a paid plan — sign in only to save your progress.