# altdns vs crt.guru: side-by-side comparison (2026)

[altdns](https://cybersectools.com/tools/altdns) is a free [external attack surface management](https://cybersectools.com/categories/external-asm) solution. [crt.guru](https://cybersectools.com/tools/crtguru) is a commercial [external attack surface management](https://cybersectools.com/categories/external-asm) solution by [Crt.guru](https://cybersectools.com/companies/crtguru). Features, integrations, deployment and the company behind each one, side by side.

Need the answer fast? [Best Attack Surface Management Solutions for Business](https://cybersectools.com/shortlists/best-attack-surface-solutions) picks Palo Alto Networks Cortex Xpanse, Microsoft Defender EASM, Mandiant Attack Surface Management and 4 more.

## Side-by-side comparison

| | altdns | crt.guru |
|---|---|---|
| Pricing model | Free | Commercial |
| Category | External Attack Surface Management | External Attack Surface Management |
| Verified | No | No |
| Deployment type | On-Premises | Cloud |
| Company size fit | Startup, SMB, Mid-Market, Enterprise | Startup, SMB, Mid-Market, Enterprise |
| GitHub stars | 2,439 | – |
| Last commit | Jan 2025 | – |
| Company | – | Crt.guru |
| Headquarters | – | – |

### Use cases and capabilities

| | altdns | crt.guru |
|---|---|---|
| Reconnaissance | Yes | – |
| TLS | – | Yes |
| SSL | – | Yes |
| PCI DSS | – | Yes |
| NIST | – | Yes |
| Security Scanning | – | Yes |
| Alerting | – | Yes |
| Security Compliance Training | – | Yes |
| Security Reporting | – | Yes |
| Vulnerability | – | Yes |
| REST API | – | Yes |

### Core features

**altdns**

No features listed.

**crt.guru**

10 features listed. Sign in on the page to see them.

### Integrations

**altdns**

No integrations listed.

**crt.guru**

4 integrations listed. Sign in on the page to see them.

## Which one fits you

Based on what each listing shows: deployment, company size, price and open source.

- [altdns](https://cybersectools.com/tools/altdns) fits if you need to run it on your own servers, you need a free product and you want an open-source product.
- [crt.guru](https://cybersectools.com/tools/crtguru) fits if you want a cloud product.

## altdns vs crt.guru FAQ

Common questions when comparing altdns vs crt.guru for external attack surface management.

### What is the difference between altdns and crt.guru?

**altdns**: A tool for generating permutations, alterations and mutations of subdomains and resolving them.

**crt.guru**: External TLS cert monitoring with expiry alerts, vuln scanning & compliance reports. Built by Crt.guru.

The table above shows where their features, integrations, deployment and company size fit differ.

### Who makes altdns and crt.guru?

**altdns** is open-source with 2,439 GitHub stars. **crt.guru** is made by Crt.guru. The vendor behind a product decides its roadmap, support, and longevity, so check each company's profile before you commit.

### Is altdns a good alternative to crt.guru?

Often, yes. altdns and crt.guru are both External Attack Surface Management products. Key differences: altdns is Free while crt.guru is Commercial, altdns is open-source. Use the table above to see where features, deployment and company size fit differ.

## Related comparisons

- [altdns vs Attack Surface Scan](https://cybersectools.com/compare/altdns-vs-attack-surface-scan)
- [altdns vs SurfaceDiff](https://cybersectools.com/compare/altdns-vs-surfacediff)
- [altdns vs DDactic Attack Surface Discovery](https://cybersectools.com/compare/altdns-vs-ddactic-attack-surface-discovery)
- [crt.guru vs Attack Surface Scan](https://cybersectools.com/compare/attack-surface-scan-vs-crtguru)
- [crt.guru vs SurfaceDiff](https://cybersectools.com/compare/crtguru-vs-surfacediff)
- [crt.guru vs DDactic Attack Surface Discovery](https://cybersectools.com/compare/crtguru-vs-ddactic-attack-surface-discovery)

## Alternatives to each

- [See all altdns alternatives](https://cybersectools.com/alternatives/altdns)
- [See all crt.guru alternatives](https://cybersectools.com/alternatives/crtguru)

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Source: https://cybersectools.com/compare/altdns-vs-crtguru

For AI agents: each product above has its own Markdown page (add .md to its URL, for example https://cybersectools.com/tools/altdns.md). Every CybersecTools shortlist is listed at https://cybersectools.com/shortlists.md.

More on altdns and crt.guru: funding, momentum, hiring and news, plus the full product and company record, are available through the Mandos MCP Server (paid plans), which connects to AI assistants: https://mandos.io/mcp?utm_source=cybersectools.com&utm_medium=compare-md