---
id: cold-start-initialization-bundle
title: Cold-start initialization and bundle weight
status: active
candidateKinds: ["cold_start"]
frameworks: ["*"]
priority: 92
citations:
  [
    "https://vercel.com/docs/functions/debug-slow-functions",
    "https://vercel.com/docs/functions/limitations",
    "https://vercel.com/docs/functions/runtimes",
  ]
maxBriefChars: 850
---

## Investigation Brief

Cold-start candidates need a code-path check, not only a project-setting check. First prove whether cold requests are paying for imports, module-scope setup, runtime choice, or dependency weight.

## Evidence To Check

Use `startTypeSplit`, `coldVsWarmLatencyP95`, and `coldByDeployment`. In source, inspect module-scope SDK setup, database/client construction, top-level network calls, heavy dependencies, runtime exports, and deployment-local changes.

## Do Not Recommend When

Do not blame cold starts when warm requests are similarly slow. Do not recommend keep-warm traffic or more memory before proving initialization or runtime pressure.

## Verification

Name the cold-start share, cold-vs-warm gap, and exact initialization, dependency, or runtime line that explains it.