Many people encounter an embarrassing message when registering a domain name: "Domain format error" or "Domain is invalid." Even though it seems fine, the registration cannot be submitted, which is especially confusing for beginners. In reality, domain name registration isn't as simple as just entering any name; it involves strict character specifications, length rules, suffix restrictions, and registrar verification mechanisms. If you don't understand these standards, you're likely to be rejected by the system during registration, or even have your ideal domain name registered by someone else.

　　Before formally explaining the specifications, it's important to understand that domain names are not randomly named on the internet. They follow unified rules set by ICANN (Internet Corporation for Assigned Names and Numbers) and various top-level domain registries, and different suffixes may have slight differences. Therefore, the reason for the error is not just a simple "format error," but may also involve multiple factors such as trademarks, sensitive words, reserved words, character compatibility, and whitelist registration.

　　Common reasons for "format errors" during domain name registration:

　　The first obstacle most users encounter is format validation failure. Registration systems typically perform real-time checks on user-submitted domain names, and error messages usually fall into the following categories:

　　The first is the inclusion of illegal characters. For example, attempting to use spaces, Chinese punctuation marks, or special symbols (such as @, #, $, etc.) in the domain name does not comply with DNS standards, so the registration system will reject it directly. Domain names are only allowed English letters a-z, numbers 0-9, and the hyphen "-". Anything else is illegal.

　　The second is the use of disallowed structures before or after the domain name, such as starting or ending with "-", or using multiple hyphens consecutively. While using hyphens in the middle is legal, many registries explicitly prohibit more than two consecutive hyphens, and do not allow "-" at the beginning or end.

　　The third is invalid length. Different domain name suffixes have specific requirements for minimum and maximum character length. For example, .com domains generally must be between 1 and 63 characters; exceeding this limit will prevent registration. Some countries and regions have additional restrictions on suffixes; for example, .cn domains historically required a minimum of 3 characters (but this has now been relaxed).

　　The fourth situation relates to Chinese domain names. While Chinese domain names can be registered, they are actually stored and resolved in Punycode format. If a user enters Chinese characters but the registrar doesn't support automatic conversion, an error will occur. Conversely, if a user manually enters punycode but misspells it, it will also be deemed invalid.

　　The fifth situation involves reserved or prohibited words. Certain domain name suffixes prohibit registration of country names, government agencies, sensitive words, legal terms, brand keywords, etc. Even if the format is correct, these words will be rejected by the system or require manual review.

　　Therefore, incorrect formatting is not simply a matter of "typos." The real reasons are often linked to character rules, technical specifications, and even legal policies.

　　Detailed Explanation of Correct Domain Name Naming Standards:

　　To ensure successful domain name registration, you can verify its legality from three dimensions: character specifications, structural rules, and suffix matching.

　　First, basic character specifications: Domain names can only consist of English letters, numbers, and hyphens. They cannot contain spaces, Chinese symbols, emojis, etc. Domain names are case-insensitive and are treated as lowercase. While some registrars support Chinese domain names, the actual resolution still relies on punycode conversion, so it's essentially still a valid character encoding.

　　Secondly, there are structural rules. A valid domain name cannot begin or end with a hyphen, and consecutive hyphens are strictly prohibited (unless it falls under the IDN domain name encoding rule "xn--"). Length must be within the allowed range, typically a minimum of 1 character and a maximum of 63 characters, but some suffixes have separate restrictions; for example, some new top-level domains support longer characters.

　　Another easily overlooked rule is semantic rules. Some country-code domains require real-name verification, organizational qualifications, or proof of local existence. For example, .cn, .gov, .edu, and .bank domains, even if formatted correctly, cannot be registered arbitrarily. If users are unaware of these prerequisites, they will still encounter "format not compliant" or "approval failed" messages.

　　Furthermore, there's a situation that falls under SEO guidelines rather than registration rules, but still affects usability. While domain names can contain numbers, a large mix of numbers and English letters reduces readability and brand memorability. Some users deliberately register seemingly "short" but difficult-to-read domain names, such as q8y3.com. While the format may be legal, it doesn't meet search engine friendliness standards.

　　Therefore, a correct domain name is not just about "being able to register," but also about long-term usability, brand recognition, and search engine optimization strategies.

　　Why does registration fail even when the domain is legal?

　　Besides format errors, there are other issues that users easily misunderstand. For example, if the system displays "Format correct but cannot be registered," this is usually not a format issue, but rather that the domain name has already been registered by someone else or is in a reserved state. Many popular suffixes and high-quality names have been pre-registered by investors, and even if there are no character errors, they cannot be re-registered.

　　Another situation is that the domain name is in a redemption period or a dispute period. Expired domain names do not immediately open for re-registration but go through stages such as expiration grace periods, redemption, and pre-release. During this period, the system will also indicate that registration is not possible.

　　Furthermore, some registrars restrict certain suffixes or phrases, such as trademark protection lists or suffixes exclusive to government agencies. If a user enters brandname.com or similar official terms, it may also be rejected by the automated review process.

　　Therefore, registration is only entirely feasible when the format is correct, the suffix is ​​valid, the domain name is not already taken, and there are no restrictions.

　　How to choose a domain name that is both legal and SEO-friendly?

　　Understanding the rules is only the first step; more importantly, you need to choose a valuable domain name. For brand or content sites, a domain name should ideally have the following characteristics:

• Short and easy to read: The shorter the domain, the easier it is to remember. Avoid mixing too many symbols and numbers.
• Semantically clear: It should reflect the business or industry attributes, making it easier to increase search relevance.
• Avoid hyphens: Although hyphens are legal, they are costly for users to remember and not conducive to word-of-mouth marketing.
• Prioritize mainstream suffixes: .com, .net, .org, country-specific suffixes, or industry-specific suffixes are more trustworthy.
• Avoid potential infringement: Do not register known brands or trademarks, otherwise, they may be subject to arbitration or cancellation.
• Consider internationalization: If targeting a global audience, choosing a generic suffix is ​​more scalable than a regional domain.
• Adapt to search habits: Keyword-based domain names still have certain SEO advantages.

　　In other words, a good domain name should not only be legal, but also usable, memorable, and easy to promote.

　　FAQs:

　　1. Can I use uppercase letters in a domain name?

　　A: Yes, but the system will automatically convert them to lowercase, which will not affect DNS resolution. Therefore, entering uppercase or lowercase letters during registration will be considered the same domain name.

　　2. Are Chinese domain names as valid as English domain names?

　　A: Technically, they resolve normally, but their promotion and compatibility are not as good as English domain names. It is recommended to use them only when the brand heavily relies on Chinese characters.

　　3. Why does entering a legal domain name still show "Unregisterable"?

　　A: It is most likely already registered, under protection, in a dispute period, or has a suffix restriction. It is not a formatting issue; you can check the status using WHOIS.

　　4. Can I use underscores, spaces, or special characters in a domain name?

　　A: No, all symbols except letters, numbers, and hyphens are illegal, and underscores are also not allowed.

　　5. What is the maximum number of characters allowed in a domain name?

　　A: Usually 63 characters, excluding the suffix. For example, exampledomainnameexample.com is within the legal range.

　　6. What should I do if my domain name is flagged as a "high-risk word" by the system?

　　A: Some words may relate to government, finance, politics, or sensitive industries. You can try changing the name or submitting it for manual review.