Cloud cost estimation for Terraform, Terragrunt, and CloudFormation. Includes optimization recommendations, budget guardrails, what-if analysis, and fully offline mode. No API key required.
Get started
brew install c3xdev/tap/c3x
c3x estimate --path /path/to/terraform
Or use Docker:
docker pull c3xdev/c3x
docker run --rm -v $(pwd):/workspace c3xdev/c3x estimate --path /workspaceSee the quick start guide for more details.
Cost estimates
$ c3x estimate --path examples/terraform --usage-file examples/terraform/c3x-usage.yml
Project: main
Name Monthly Qty Unit Monthly Cost
aws_db_instance.postgres
├─ Database instance (on-demand, Multi-AZ, db.r5.large) 730 hours $365.00
└─ Storage (general purpose SSD, gp3) 200 GB $46.00
aws_instance.api
├─ Instance usage (Linux/UNIX, on-demand, m5.xlarge) 730 hours $140.16
├─ root_block_device
│ └─ Storage (general purpose SSD, gp2) 100 GB $10.00
└─ ebs_block_device[0]
└─ Storage (general purpose SSD, gp3) 500 GB $40.00
aws_nat_gateway.main
├─ NAT gateway 730 hours $32.85
└─ Data processed Monthly cost depends on usage: $0.045 per GB
aws_lb.api
├─ Application load balancer 730 hours $16.43
└─ Load balancer capacity units Monthly cost depends on usage: $5.84 per LCU
OVERALL TOTAL $650.44
Cost diffs
$ c3x diff --path . --compare-to main
Project: main
~ aws_instance.api
├─ Instance usage (Linux/UNIX, on-demand, m5.xlarge -> m6i.2xlarge) +$170.24 ($140.16 -> $310.40)
└─ ebs_block_device[0]
└─ Storage (general purpose SSD, gp3, 500 -> 1000 GB) +$40.00 ($40.00 -> $80.00)
Monthly cost change: +$210.24 ($650.44 -> $860.68)
Optimization recommendations
c3x recommend --path .3 recommendation(s) found:
1. Upgrade to newer instance generation (m5.xlarge -> m7i.xlarge)
Resource: aws_instance.web (aws_instance)
The m7i family has better price-performance than m5.
2. Switch EBS volume from gp2 to gp3
Resource: aws_ebs_volume.data (aws_ebs_volume)
gp3 volumes are up to 20% cheaper with better baseline performance.
3. Consider VPC endpoints to reduce NAT Gateway costs
Resource: aws_nat_gateway.main (aws_nat_gateway)
NAT Gateway charges $0.045/GB. VPC endpoints can eliminate these charges.
Budget guardrails
Enforce cost limits in CI/CD pipelines. No paid subscription required.
c3x estimate --path . --budget 1000 c3x diff --path . --compare-to baseline.json --budget-increase 20
What-if analysis
Test cost impact of changes without modifying Terraform code.
c3x estimate --path . --what-if 'aws_instance.web.instance_type=m6i.8xlarge' c3x estimate --path . --what-if 'aws_db_instance.main.multi_az=true'
PR comments
Post cost estimates in pull requests. Two steps, no secrets.
- uses: actions/checkout@v4 - uses: c3xdev/setup-c3x@v1 with: path: .
Install the C3X Cloud app for branded comments with the C3X logo. See a live example. Also supports GitLab, Bitbucket, Azure Repos, Atlantis, and Spacelift.
Offline mode
Download pricing data once. Estimate without network calls.
c3x pricing sync --providers aws,azure
c3x estimate --path . --offlineSelf-hosted pricing API
Run your own pricing API that scrapes directly from AWS, Azure, and GCP.
export C3X_PRICING_API_ENDPOINT=http://localhost:4000 c3x estimate --path .
Supported resources
Over 1,100 Terraform resources across AWS, Azure, and Google Cloud. Usage-based resources (Lambda, S3, data transfer) are supported via usage files.
Roadmap
- Compare estimates to real cloud bills (AWS Cost Explorer, Azure Cost Management)
- Pulumi, AWS CDK, Azure Bicep support
- Historical cost tracking across commits and PRs
- VS Code and JetBrains inline cost estimates
Contributing
Open a thread in GitHub Discussions before submitting a PR. See the contribution guide for details.