When your function uses too much CPU time, Vercel pauses its execution periodically to stay within limits. This means your function may take longer to complete, which, in a worst-case scenario, can cause timeouts or slow responses for users.

CPU throttling itself isn't necessarily a problem as it's designed to keep functions within their resource limits. Some throttling is normal when your functions are making full use of their allocated resources. In general, low throttling rates (under 10% on average) aren't an issue. However, if you're seeing high latency, timeouts, or slow response times, check your CPU throttling metrics. High throttling rates can help explain why your functions are performing poorly, even when your code is optimized.

To reduce throttling, optimize heavy computations, add caching, or increase the memory size of the affected functions.

External APIs

You can use the External APIs tab to understand more information about requests from your functions to external APIs. You can organize by number of requests, p75 (latency), and error rate to help you understand potential causes for slow upstream times or timeouts.

External APIs Recipes

Investigate Latency Issues and Slowness on Vercel

Middleware

The Middleware observability tab shows invocation counts and performance metrics of your application's middleware.

Observability Plus users receive additional insights and tooling:

• Analyze invocations by request path, matched against your middleware config
• Break down middleware actions by type (e.g., redirect, rewrite)
• View rewrite targets and frequency
• Query middleware invocations using the query builder

Edge Requests

You can use the Edge Requests tab to understand the requests to each of static and dynamic routes through the global network. This includes the number of requests, the regions, and the requests that have been cached for each route.

It also provides detailed breakdowns for individual bots and bot categories, including AI crawlers and search engines.

Additionally, Observability Plus users can:

• Filter traffic by bot category, such as AI
• View metrics for individual bots
• Break down traffic by bot or category in the query builder
• Filter traffic by redirect location
• Break down traffic by redirect location in the query builder

Fast Data Transfer

You can use the Fast Data Transfer tab to understand how data is being transferred within the global network for your project.

For more information, see Fast Data Transfer.

Image Optimization

The Image Optimization tab provides deeper insights into image transformations and efficiency.

It contains:

• Transformation insights: View formats, quality settings, and width adjustments
• Optimization analysis: Identify high-frequency transformations to help inform caching strategies
• Bandwidth savings: Compare transformed images against their original sources to measure bandwidth reduction and efficiency
• Image-specific views: See all referrers and unique variants of an optimized image in one place

For more information, see Image Optimization.

The External Rewrites tab gives you visibility into how your external rewrites are performing at both the team and project levels. For each external rewrite, you can see:

• Total external rewrites
• External rewrites by hostnames

Additionally, Observability Plus users can view:

• External rewrite connection latency
• External rewrites by source/destination paths

To learn more, see External Rewrites.

Microfrontends

Vercel's microfrontends support allows you to split large applications into smaller ones to move faster and develop with independent tech stacks.

The Microfrontends tab provides visibility into microfrontends routing on Vercel: