Is your NAT gateway bill avoidable?

Paste one row per NAT gateway and destination — GB per month to S3, DynamoDB, ECR, CloudWatch Logs, anything — and get what the NAT gateway costs, the free S3 and DynamoDB gateway endpoints you are missing, the interface endpoints that beat $0.045/GB after their hourly fee, the idle gateways and the ready-to-paste aws ec2 create-vpc-endpoint commands.

Nothing is uploaded and AWS is never contacted. The text box is analysed in this browser and never leaves your device. The GB per destination is the number you supply, so traffic you did not label counts as internet.

1. Paste your NAT traffic

Rows of gateway, destination (s3, dynamodb, ecr, logs, sts, ssm, kms, internet…), GB per month, VPC (optional)

Prefer a CLI, or want a CI check?

Same logic, zero dependencies, one command — reads a file or stdin:

node cli.mjs analyze nat.csv
cat nat.csv | node cli.mjs analyze -
node cli.mjs analyze nat.csv --azs 3 --region eu-west-1
node cli.mjs analyze nat.csv --fail-on warn      # exit 1 on any avoidable NAT spend
node cli.mjs analyze nat.csv --json --prices my-prices.json

Get cli.mjs and engine.mjs — Node 18+, nothing to install, no network call. More: NAT gateway vs VPC endpoint: what it costs and when to switch.

What's recognised

Input	Handling

Prices are illustrative and dated; edit them with --prices in the CLI. Other regions, cross-AZ data transfer, data transfer out to the internet, endpoint policies and PrivateLink services outside AWS are not modelled.

Common questions

Does this connect to my AWS account?

No. It reads the rows you paste and never contacts AWS. It cannot see your real invoice, Savings Plans, private pricing or free tier, so every dollar figure is the rows you pasted times list prices you can edit.

How do I get the GB per destination?

Turn on VPC Flow Logs for the NAT gateway's network interface and sum bytes by destination, or in Cost Explorer filter usage type NatGateway-Bytes by gateway. Label the destinations you can tell are AWS services (S3, DynamoDB, ECR, CloudWatch Logs, STS, SSM); everything else counts as internet and is never recommended for an endpoint.

Why is S3 through a NAT gateway such a common waste?

A NAT gateway charges $0.045 per GB processed for every byte, including bytes to S3 in the same region, while a gateway endpoint for S3 or DynamoDB is free and is only a route-table entry. Terabytes of S3 reads from private subnets cost hundreds of dollars a month for nothing.

When is an interface endpoint worth it?

An interface endpoint costs $0.01 per hour per AZ (about $7.30 a month per AZ) plus $0.01 per GB, against $0.045 per GB through the NAT gateway. It breaks even at roughly 209 GB a month per endpoint per AZ, and services such as ECR, SSM and ECS need two or three endpoints, which the tool counts.

Is my data uploaded anywhere?

No. The browser page analyses the text in your own browser and never sends it anywhere. The CLI reads a local file or stdin and makes no network call.