Subdomain Takeover Checker
Fast, accurate and free online subdomain takeover checker tool running directly in your browser.
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Checking for subdomain takeover
This tool helps detect subdomains that point to resources on third-party providers that no longer exist (e.g. GitHub Pages, Heroku, S3, Azure, Shopify). The analysis is heuristic - it is based on DNS records (CNAME) and HTTP responses. Only use to audit your own domains or where you have formal permission.
Analysis options
No subdomains with clear signals of potential takeover were detected based on the tests performed. Please note that the analysis is heuristic and does not replace a full security audit.
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Related tools
Other tools you may find usefulSubdomain Takeover Checker - a quick test of the risk of subdomain takeover
Subdomain Takeover Checker is a simple but very useful online tool that scans selected subdomains and checks whether they do not look abandoned, poorly configured or related to services that no longer exist, which in certain scenarios may lead to unwanted takeover of the subdomain by unauthorized persons.
What is a subdomain takeover in simple words
A subdomain takeover is a situation in which a subdomain appears to be properly configured from the DNS or HTTP side, but there is no longer an active service or application on the other side, for example, an account on an external platform has expired, a SaaS site has been deleted, or the old infrastructure has been disconnected, and the records still point to the same place and can potentially be used by someone else in a way that is contrary to owner's intention.
For the end user, this means that someone unauthorized may try to link their own content to an address belonging to your domain, which in extreme cases may lead to impersonating the company, collecting login details, displaying malicious content or simply ruining the brand's reputation in the eyes of visitors.
- The subdomain points to an external service that is no longer in use or has been disabled.
- CNAME or A DNS records still exist even though the old application has been removed from the provider dashboard.
- The browser shows messages like no target configuration or no application at this address.
- The team migrated the project but did not clear all historical subdomain and integration records.
- An organization has many teams and it is difficult to manually control which subdomains are still active and which are no longer active.
How Subdomain Takeover Checker works from the user's side
The tool has been designed so that anyone who can paste a list of addresses can quickly check their subdomains, without having to use complex console tools or extensive monitoring systems, therefore the whole process comes down to a few transparent steps that can be repeated as often as needed in everyday work on website security.
1. Paste the list of subdomains for analysis
In the main field, enter one or many subdomains, each in a separate line, for exampleblog.yourdomain.pl, app.yourdomain.plor addresses likepromo.yourdomain.pl. You don't have to provide the entire DNS configuration, all you need is the address that your websites actually use or you have it saved in the website configuration.
This is a convenient scenario, for example, after reviewing the DNS panel, after project migration, or after cleaning up old marketing campaigns and test environments.
2. You select the type of tests and the timeout
By default, Subdomain Takeover Checker performs both the DNS test and HTTP control calls, but you can select whether you are only interested in checking DNS records, only HTTP responses, or the full set of checks. Additionally, you set a server response timeout, thanks to which the tool will not hang indefinitely when some subdomain responds very slowly.
3. You run the scan with one click
After selecting the option, one click is enough for the scanner to start browsing the entered subdomains, checking their DNS resolution, analyzing CNAME and A records, and, if necessary, making HTTP queries that help detect characteristic responses indicating incomplete configuration or lack of applications on the target side of the service.
4. You receive a risk summary report
After the scan is completed, you will see a summary summary, which will include, among other things, the number of subdomains examined, the number of entries with a valid DNS response, the number of items classified as potential risk, and a list of service providers that were recognized based on the host configuration or HTTP response.
What exactly does Subdomain Takeover Checker check
To detect potentially risky scenarios, the tool combines basic information from the DNS and HTTP layers, and then compares them with each other and with typical behavior patterns of cloud and hosting services, such as the lack of an assigned application, the lack of a resource under the specified host, or messages suggesting that the address can only be configured.
DNS module
In the DNS part, the scanner checks whether the subdomain actually has records that resolve correctly, what its CNAME record looks like, if any, and what IP addresses are assigned in the form of A records. On this basis, the tool is able to assess whether the subdomain points to a specific provider or type of service, which later helps in interpreting whether an application is actually running behind the indicated address or whether there are signs of lack of configuration.
HTTP Module
In the HTTP layer, Subdomain Takeover Checker performs control requests, saves response codes, the address to which the final connection was made and a fragment of the response content. The tool does not try to modify or change anything on the server side, it only observes the responses, which in many cases are enough to assess whether we are dealing with a normally functioning website or a technical message indicating the lack of the target configuration.
How to read risk levels in a report
To make the work easier for non-technical people, the Subdomain Takeover Checker report is not limited to raw HTTP codes and DNS records, but groups the results into a few simple categories that clearly show which subdomains require more urgent analysis and which look safe and in line with the team's expectations.
| Risk Level | What the scanner sees | How to respond in practice |
|---|---|---|
| High | The combination of DNS and HTTP responses suggests that the subdomain may be associated with a service that is not fully configured. | Verify your configuration with your domain team as soon as possible and remove or correct any risky entries. |
| Medium | There are signs that the configuration is ambiguous, for example, the subdomain points to a service no longer in use or generates technical messages. | Scheduling a review soon is a good idea, especially if the subdomain was of business importance. |
| Info | The responses look normal, but it is worth having them in the report to see the full picture of connected subdomains and providers. | This is not an alarm, rather additional information that will help with periodic security audits. |
Who is Subdomain Takeover Checker for
Although the topic of subdomain takeover is mainly associated with the world of security, in practice such a tool can be used by very different people in the organization, from engineers responsible for DNS and infrastructure, through product owners and marketing teams, to freelancers and small companies that simply want to be sure that their subdomains have not been left in an unclear state by old projects.
Security Specialists
Quickly scan a large number of subdomains for potential risks that can later be incorporated into a formal security audit or compliance testing report.
DevOps teams and engineers
A simple way to check whether service migrations or infrastructure changes have left behind old DNS records and subdomains leading to a no longer active configuration.
Product owners and website owners
Ability to verify whether the addresses used in campaigns, landing pages and user panels still work as expected and do not unnecessarily open an additional risk window.
Frequently asked questions about Subdomain Takeover Checker
Is this tool safe for my infrastructure
Yes, Subdomain Takeover Checker only performs standard DNS and HTTP queries, which are exactly what regular browsers and monitoring systems send anyway. The tool does not make any changes on the server side and does not modify the configuration, so it does not affect the operation of your services, but only observes the responses that are already publicly available on the network.
Can I scan any domains I find on the internet
The tool should only be used for domains and subdomains for which you have administrative rights or explicit consent to perform testing. Scanning other people's resources without permission may violate terms of service and local regulations, so always focus on your own infrastructure or test environments provided specifically for security purposes.
How Often Should You Run Subdomain Takeover Checker
It's a good habit to scan subdomains after major infrastructure changes, such as after migrating to a new cloud, introducing a new service, or ending a marketing campaign that used multiple addresses. In larger organizations, it is worth including this tool in a periodic security review, for example once a month or quarterly.
Does the tool suggest specific remediation steps
Subdomain Takeover Checker focuses on identifying suspicious cases and assigning them a risk level, while detailed actions depend on the technology, service and supplier you use. The report from the tool is a starting point for technical teams who know your infrastructure and, on this basis, will make decisions about deleting unnecessary records, changing the service configuration or cleaning up the DNS panel.
Scan your subdomains before someone else does it for you
Paste your list of addresses, select DNS and HTTP tests, and run the Subdomain Takeover Checker to quickly see which subdomains look safe and which may require additional attention from your team. One simple scan can significantly reduce the risk of surprising issues with abandoned records and unclear configuration.