AWS Error NoSuchKey: S3 NoSuchKey

Identify: does your log match?

NoSuchKey: The specified key does not exist.
    at de_NoSuchKeyRes (/app/node_modules/@aws-sdk/client-s3/dist-cjs/index.js:4908:21)
  '$fault': 'client',
  '$metadata': { httpStatusCode: 404, requestId: 'R7X1N9M2Q4K8P0ZT', attempts: 1 },
  Code: 'NoSuchKey',
  Key: 'uploads/2026/10/report final.pdf'

1. High

   Key built with wrong encoding

   Passing a URL-encoded key (report%20final.pdf) or a + for spaces to the SDK, which encodes again. S3 keys are literal strings.

2. Medium

   Leading slash or wrong prefix

   /uploads/a.png and uploads/a.png are different keys. Path joins often add the slash.

3. Low

   Read before write completes

   Reading right after an async upload that has not finished, or from the wrong region/bucket.

Fix

const obj = await s3.send(new GetObjectCommand({ Bucket, Key }));
return new Response(obj.Body as ReadableStream);

import { GetObjectCommand, NoSuchKey } from '@aws-sdk/client-s3';

try {
  const obj = await s3.send(new GetObjectCommand({ Bucket, Key }));
  return new Response(obj.Body!.transformToWebStream());
} catch (err) {
  if (err instanceof NoSuchKey) return new Response('Not found', { status: 404 });
  throw err;
}

Verify: reproduce it on purpose

$ aws s3api get-object --bucket "$BUCKET" --key does/not/exist.txt /tmp/x

Prevent

• Store the exact key returned at upload time.
• Use HeadObject to check existence cheaply.
• Grant s3:ListBucket so missing keys return 404, not 403.