Could not connect to the endpoint URL (DynamoDB)

TL;DR — botocore couldn't open a connection to the DynamoDB endpoint it resolved. Almost always a wrong --endpoint-url, DynamoDB Local not running, a bad/typo'd region producing a nonexistent hostname, or no network path (offline, VPC, security group). Point at a reachable endpoint and confirm something is listening.

What it means

botocore.exceptions.EndpointConnectionError: Could not connect to the
endpoint URL: "http://localhost:8000/"

boto3/botocore builds the DynamoDB endpoint URL from the region (or your explicit endpoint_url) and then fails to establish a TCP/HTTP connection to it. Unlike an auth or validation error, the request never reached a running service. It surfaces both against DynamoDB Local (emulator down / wrong port) and real AWS (bad region hostname or blocked network).

Why it happens

• DynamoDB Local isn't running — you passed --endpoint-url http://localhost:8000 but the emulator isn't up on that port (see connection refused).
• Wrong endpoint URL — a typo, wrong port, or https where the local emulator serves http.
• Bad region — a misspelled region (us-east-11) resolves to a hostname that doesn't exist, so the connection can't be made.
• No network path — offline, or DynamoDB traffic blocked by a VPC endpoint, security group, or network ACL.
• Cross-container / cross-host — from inside Docker, localhost is the container itself, not the host or the DynamoDB Local service.

How to fix it

1. Confirm what's listening at the endpoint:

   curl http://localhost:8000    # DynamoDB Local answers with a small response

2. Fix the endpoint URL — correct host, port (8000 by default), and scheme (http for Local).
3. Check the region spelling for real AWS, and make sure you have a network route (VPC endpoint / security group rules allow DynamoDB).
4. In Docker, use the service name or host.docker.internal instead of localhost.
5. Talking to real AWS? Drop the --endpoint-url override entirely and let botocore build the correct regional endpoint.

Related errors

• Could not connect to DynamoDB Local (ECONNREFUSED) — the Node/JS equivalent of a refused local connection.
• Missing region in config — no region, so the SDK can't build an endpoint at all.
• Learn: Running DynamoDB Local · Connecting to DynamoDB Local / LocalStack