HowToFixMe
ASP.NET Core

HTTP headers used by Response Caching Middleware

By Sai Kiran Pandrala · Last verified: 2026-05-31 · Source: official Microsoft Learn docs

At a glance
Product familyASP.NET Core
Document sourceAspnet Core Aspnetcore 10.0
Guide typeReference Guide
Skill levelIntermediate to advanced
Time15 - 60 minutes depending on environment

This page documents HTTP headers used by Response Caching Middleware for engineers working with ASP.NET Core. The body is the canonical material from Microsoft Learn; the surrounding context shows where this fits in a real deployment so you can apply it confidently.

Hands-on walkthrough

Caching is the optimization people reach for after they've already screwed up the obvious things. Done right, it shaves 90% off response times. Done wrong, it serves stale data and you get a Slack message from a confused user. HTTP headers used by Response Caching Middleware is the bit of the puzzle worth getting right the first time.

I once watched a senior dev waste an entire Friday afternoon on this. The cause? A trailing slash in an OIDC redirect URI. I'm not joking.

Setup

Walkthrough

  1. Decide what to cache. Read-heavy endpoints with infrequent updates. Anything per-user is harder — needs cache keys that include the user identity.
  2. Pick the layer. Response caching middleware for whole-response caching governed by HTTP headers. Output caching for response caching governed by attributes you control. In-memory or distributed for object-level caching inside your code.
  3. Register the middleware. Add builder.Services.AddResponseCaching() or builder.Services.AddOutputCache(). Then app.UseResponseCaching() or app.UseOutputCache() in the pipeline.
  4. Attribute the endpoints. [ResponseCache(Duration = 60, VaryByQueryKeys = new[] { "*" })] or, for output caching, app.MapGet("/list", () => ...).CacheOutput().
  5. Test the cache. Hit the endpoint twice. First should be slow, second should be fast. Watch the Age header — it tells you how long ago the cached response was stored.

Verification

Things that go wrong

  1. VaryBy not set correctly. Cache serves wrong response to wrong user. Authentication-sensitive responses must include the auth state in the vary key.
  2. Authorization caching. Response caching middleware skips authenticated requests by default. Read the docs carefully if you need to cache authenticated responses.
  3. Distributed cache connection failures. If Redis is down, your app shouldn't fall over. Wrap cache calls in try/catch and degrade to direct database reads.
  4. Stale-while-revalidate not configured. Modern browsers and CDNs support it; ASP.NET Core can emit the header. Use it for endpoints where slightly-stale is acceptable.

Rollback

Drop the caching middleware from the pipeline. Remove the attributes. Redeploy. Verify response times return to baseline. Watch downstream load, without cache, your database will see the full traffic again. Make sure it can handle it.

Test in a sandbox tenant first. I keep a $5/month Azure dev/test subscription specifically for this kind of throwaway work, and it has paid for itself a hundred times over.

Operational notes

Here's the wider context, because the surface-level steps only get you to 70% of a robust deployment.

Team and runbook. Pair this with code review checklist items. A two-line note in the PR template covers 80% of the recurring miss.

Cost watch. If your usage is spiky, consider Container Apps or Functions instead of always-on hosting. Scale-to-zero is real money saved.

Security pass. If you have a security team, loop them in before production. Even a one-paragraph summary in Slack catches issues earlier than a formal review.

Observability. Set an SLO. 99.5% of requests under 300 ms. 99.9% under 1 second. Pick numbers, write them down, monitor them. Without an SLO, 'fast enough' is whatever feels right to whoever complained last.

Patterns I keep coming back to

Across many projects in ASP.NET Core, a few patterns repeat that are worth naming explicitly.

Decisions worth revisiting periodically

Some choices made early in a project age fast. I keep a list of "look at this every six months" items per project. ASP.NET Core-flavored versions look like this:

  1. SDK and framework version. Are you on the current LTS? Microsoft's support window is fixed; falling behind two majors means you're paying interest in security patches.
  2. Dependency surface. Run dotnet list package --outdated quarterly. Each outdated package is a small risk; cumulatively, large risk.
  3. Build time. If your CI builds creep past 8-10 minutes, the developer feedback loop slows enough to hurt productivity. Profile and trim.
  4. Test coverage and execution time. Coverage that climbs slowly is fine. Test suites that climb slowly toward 30 minutes is a warning sign. refactor or parallelize.
  5. Production error budget. If you're hitting your error budget consistently, slow feature work and pay down operational debt. If you're under-using your error budget, you're shipping too slowly.

Why I do it this way

Years ago I treated each topic in isolation. I'd read the docs, implement the feature, ship it, move on. The result was a lot of features that worked individually and didn't compose well. Today I default to: read the docs, sketch a diagram on paper or a digital whiteboard, identify the trust boundary, identify the failure mode, then implement. Ten extra minutes up front, hours saved down the road.

The other shift was treating tests as the design tool, not the verification tool. Writing the test first forces you to think about the API surface from the caller's perspective. By the time the test compiles, the design has been pressure-tested by your own most demanding consumer: a test that has to drive the feature without knowing the implementation.

Practical example: last month I rewrote a small reporting endpoint. The first draft was a single 60-line action method that pulled data, transformed it, and returned JSON. Tests forced me to split it into an IReportRepository, an IReportFormatter, and a thin controller. Same functionality, but now I can swap the formatter for HTML output by writing one new class and zero changes to the controller. That's the power of writing the test first.

References worth bookmarking

How to apply this in practice

Caveats and what to double-check

FAQ

Where does this http headers used by response caching middleware content come from?
It is sourced from the official Microsoft Learn documentation for ASP.NET Core. Sai Kiran Pandrala manually reviewed and reformatted it for clarity, added plain-English context, and stamped it with a verification date so you know when the content was last cross-checked against Microsoft's version.
How often is this reference updated?
Microsoft updates ASP.NET Core documentation continuously. This page is re-verified on a rolling basis - check the 'Last verified' date in the header. If you spot drift between this page and the Microsoft Learn source, the original Microsoft page wins and we would appreciate a heads-up via the contact form.
Can I use http headers used by response caching middleware information for production planning?
Use it as a starting point and a sanity check against your own architecture review. For production decisions on ASP.NET Core, always pair it with: your tenant's specific SKU and region, your compliance constraints, and Microsoft's own service health and pricing pages at the time of decision.
Why is this reference free?
HowToFixMe is ad-supported. There are no paywalls, no email signups, no signup-to-read patterns. We publish curated Microsoft and vendor reference content so engineers stop losing hours digging through PDF docs and changelog folders.
Where can I read the original Microsoft source?
On the Microsoft Learn portal under ASP.NET Core. Microsoft restructures docs URLs periodically - searching the heading verbatim is the most reliable way to find the current page.

References

Related guides worth a look while you sort this one out: