---
title: Investigate latency issues and slowness on Vercel
description: Learn how to use Observability to investigate latency issues and slowness on Vercel.
url: "https://vercel.com/kb/guide/investigate-latency-issues-and-slowness"
published: 2025-11-03
last_updated: 2025-11-11
authors: DX Team
install_vercel_plugin: npx plugins add vercel/vercel-plugin
---

**Problem**: One of your functions is timing out, not serving responses quickly enough, or otherwise alerting.

You can use [Observability](/docs/observability) to investigate and understand slow responses from your functions and its effects on function duration, error rates, and consumption. To do so:

1. From your [dashboard](/dashboard), select the project you want to investigate.
   
2. Navigate from your dashboard to the **Observability** tab.
   
3. Choose **External APIs** and set an appropriate time range filter (e.g. last 6 hours).
   
4. From the list, sort by **P75 duration** to find hosts with the slowest response times, e.g. `mycms.com`: {' '}
   
   ![sort-by-p75-light.png](https://images.ctfassets.net/hjgychtc108g/4ctc1dPPUprSiLWh3fIpRn/f10681c36ad3d839c97ddda1c438eff0/sort-by-p75-light.png)
   
   Media
   
5. Select the hostname with high duration or error rate: {' '}
   
   ![select-hostname-light.png](https://images.ctfassets.net/hjgychtc108g/4TAdIfpNSODOuTeHP1AVxX/4321715cee08a539cbf3760d3dd77599/select-hostname-light.png)
   
   Media
   
6. You can see a distribution of requests over time, as well as their latency. When selecting Functions, you can see which of your function routes sent the requests to the slow external API and navigate to the appropriate view right away.
   

## More resources

- [Observability overview](/docs/observability)
  
- [Observability limits and pricing](/docs/observability/limits-and-pricing)

## Related Documentation

- [Observability](/docs/observability)

## More Observability guides

- [Trace and debug eve agent runs](/kb/guide/trace-and-debug-eve-agent-runs): Inspect eve traces in Vercel Agent Runs, control captured content, export OpenTelemetry spans, and test fixes with regression evals.
- [Capture AI SDK token usage, tool calls, and cost with evlog](/kb/guide/ai-sdk-and-evlog): Record AI SDK usage with evlog, add cost estimates and request context, and investigate expensive or failed requests.
- [How to effectively load test your application on Vercel](/kb/guide/how-to-effectively-load-test-your-vercel-application): Learn how to safely load test your Next.js app on Vercel. This guide covers realistic, policy-compliant testing of routes, caching, middleware, and databases to uncover performance issues without impacting Vercel’s infrastructure.

## Reference Architecture

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