JUHE API Marketplace

REST API Caching Strategies

4 min read

Introduction: Why caching is critical for REST APIs

APIs power everything from fintech dashboards to weather widgets. But high request volumes can strain your backend and slow down responses. Caching helps you serve repeated requests faster, reduce server load, and cut costs.

In this post, we’ll show you how to implement ETag and Cache-Control to boost your REST API’s performance.

The core benefits of API caching

  • Lower latency: Serve repeated responses instantly from caches.
  • Reduce backend load: Save database calls and CPU cycles.
  • Cut bandwidth: Send small validation requests instead of full payloads.
  • Improve uptime: Cache prevents total slowdowns during spikes.

ETag: Your version fingerprint

ETags are opaque strings that represent the specific version of a resource. Think of them as unique fingerprints for each payload version.

How ETag works

  1. Server returns an ETag header alongside the resource.
  2. Client stores the ETag with the cached content.
  3. On future requests, client sends If-None-Match: <etag>.
  4. Server compares ETag:
    • If unchanged: returns 304 Not Modified.
    • If changed: sends updated resource and new ETag.

Weak vs strong ETags

  • Strong ETag: Byte-for-byte match. Useful for binaries or precise content.
  • Weak ETag: Prefixed with W/. Indicates semantically equivalent content that may differ in bytes.

Implementation tips

  • Use hashes or version IDs as ETag values.
  • Avoid exposing sensitive info in ETag.
  • Always return ETag for cacheable GET responses.

Example response headers: ETag: "v2-202406" Cache-Control: max-age=3600

Cache-Control: The time-to-live boss

Cache-Control tells clients and intermediaries how—and for how long—to cache responses.

Common directives

  • max-age=<seconds>: Time in seconds a resource is considered fresh.
  • no-cache: Resource must be revalidated before use.
  • must-revalidate: Forces revalidation after freshness expires.
  • public / private: Controls whether shared caches can store the response.

When to use each

  • Short max-age for fast-changing data like currency exchange rates.
  • no-cache when data correctness is critical (e.g., personal profile info).
  • must-revalidate to ensure stale content isn’t used without checking.

Example: Cache-Control: public, max-age=300, must-revalidate

Combining ETag and Cache-Control

Strong caching = time-based + content-based strategies.

  • Cache-Control speeds up most requests without a server hit.
  • ETag ensures correctness once stale.
  • Together, they optimize both performance and data accuracy.

Example flow for a GET request to a currency endpoint:

  • Within 5 minutes (max-age=300): Serve from cache.
  • After 5 minutes: Client revalidates with If-None-Match. If ETag matches, server returns 304; otherwise, it returns a fresh representation and a new ETag.

Practical workflow for adding caching to an API

  1. Identify cacheable endpoints: read-heavy GETs.
  2. Choose TTL: based on update frequency and business risk.
  3. Return ETag and Cache-Control: always in responses.
  4. Handle conditional requests: implement If-None-Match logic.
  5. Test with curl and browser DevTools.

Example with JuheAPI

For https://hub.juheapi.com/exchangerate/v2/, you might:

  • Set Cache-Control: public, max-age=300.
  • Generate ETag from the latest exchange-rates batch ID (or a hash of the payload).
  • On If-None-Match, compare the batch ID and return 304 if unchanged.

Monitoring and tuning cache performance

  • Track hit/miss ratio: Aim high (e.g., 80%+) for static or slow-changing data.
  • Watch for stale data complaints: Shorten TTL or add must-revalidate.
  • Analyze logs: Spot frequently changing resources and lower their TTL.
  • Instrument upstream and downstream: Measure origin latency vs cached latency.

Common pitfalls to avoid

  • Caching non-idempotent responses: Only cache safe GETs.
  • Ignoring Vary headers: If response changes based on headers (e.g., Accept-Encoding, Authorization, Accept-Language), include Vary accordingly.
  • Overly long TTL: Risk serving outdated data.
  • Skipping validation: No ETag means no cheap revalidation.
  • Forgetting privacy: Use private for user-specific content to avoid shared cache leaks.

Conclusion: Faster APIs, happier developers

Caching is a simple lever with outsized impact. ETag and Cache-Control give you fine-grained control over freshness and validation.

Whether you’re building your own backend or consuming APIs like those from JuheAPI, caching strategies can make your app snappier and your infrastructure leaner.

Start small: add ETag, tune your Cache-Control, and watch your API speed up.