YARA Rule Builder
Build a YARA rule from strings, hexadecimal patterns and file characteristics, with correct modifiers, a condition clause and the metadata a shareable rule needs.
Last reviewed by the Radiatus Cloud team
Strings
Condition
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Pattern matching for files, written to be shared
YARA describes families of files by the patterns they contain. A rule declares strings, which may be text, hexadecimal byte sequences or regular expressions, and a condition combining them with file properties. Malware analysts, incident responders and threat intelligence teams use it as the common language for detection logic, and rules travel between organisations far more easily than any vendor specific signature format.
Specificity is the whole craft
A rule matching a common string produces thousands of false positives and gets disabled within a day. A rule matching a single hardcoded value is defeated by recompilation. The useful middle ground combines several moderately distinctive patterns with a file size bound and a format check, so the rule describes a family rather than a sample. Requiring several strings to appear together, rather than any one of them, is the single most effective way to raise precision.
Metadata is not optional in practice
A rule circulating without an author, a date, a description and a reference is unusable six months later when it fires and nobody can say what it was written for or whether it is still relevant. Including the hash of the sample the rule was derived from lets the next person verify it still matches what it was built from. Every mature rule collection enforces this, and it costs nothing at authoring time.
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Frequently Asked Questions
What do the string modifiers mean?
ascii and wide select the encoding, and wide matches UTF-16, which is what Windows binaries mostly contain. nocase makes the match case insensitive. fullword requires word boundaries. base64 matches the encoded form. Combining wide and ascii is standard for Windows samples.
How do I avoid false positives?
Require several distinctive strings together rather than any one, bound the file size, check the file format with a magic byte test, and test against a large corpus of clean files before deploying. A rule that has not been tested against clean data has an unknown false positive rate.
Should I match on hashes?
A hash rule matches exactly one file and is defeated by a single byte change, so it is useful for a specific known sample and useless as a family rule. Hashes belong in the metadata as provenance rather than in the condition.
What is the filesize condition for?
It bounds the rule so it never scans or matches files far outside the expected range, which both reduces false positives and speeds up scanning considerably across a large file set.
Where can I run these rules?
The YARA command line tool, most endpoint detection platforms, VirusTotal Livehunt and Retrohunt, Volatility for memory images, and many sandboxes. This builder generates the rule text; it does not scan anything.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Add the strings and conditions you want to match and copy the generated YARA rule.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
Password Strength Checker
SecurityMeasure password strength by entropy and pattern analysis rather than character-class rules. Checked entirely in your browser.
Password Generator
SecurityGenerate strong random passwords and passphrases in your browser using the Web Crypto API. Nothing is transmitted, logged or stored.
Hash Generator
SecurityGenerate MD5, SHA-1, SHA-256 and SHA-512 hashes in your browser. Compare checksums and verify file integrity with nothing uploaded to a server.