Unicode Technical Report (UTR)

What is a Unicode Technical Report (UTR)?

A Unicode Technical Report (UTR) is an informative document published by the Unicode Consortium that provides guidance, analysis, data, or algorithms related to Unicode text processing. UTRs are not normative — they do not define requirements that implementations must follow to be conformant — but they carry significant authority as the Consortium's official technical recommendations and are widely implemented across platforms and programming languages.

UTRs are numbered sequentially and cover topics ranging from security vulnerabilities to text layout algorithms. They are distinct from the Unicode Standard itself and from Unicode Standard Annexes.

Key UTRs

UTR #39 — Unicode Security Mechanisms Perhaps the most security-critical Unicode document, UTR #39 defines algorithms and data for detecting potentially dangerous uses of Unicode in identifiers and text. It introduces the concepts of confusables, mixed-script detection, and identifier profiles. The associated data files (confusables.txt, intentional.txt) are used by browsers, programming language parsers, and security tools worldwide.

UTR #36 — Unicode Security Considerations A companion to UTR #39, this report catalogs the full range of security problems that arise from Unicode's complexity: visual spoofing, delimiter confusion, canonicalization attacks, overlong encodings (historical UTF-8 issue), and more. Essential reading for anyone building security-sensitive systems that process Unicode text.

UTR #29 — Unicode Text Segmentation (now a UAX) Originally a Technical Report, UTR #29 defined rules for finding grapheme cluster, word, and sentence boundaries. It has since been promoted to a Unicode Standard Annex (UAX #29), reflecting its normative status. Its history as a UTR illustrates the lifecycle: TR → promoted to UAX as implementations matured.

UTR #14 — Unicode Line Breaking Algorithm (now a UAX) Similarly, the line breaking algorithm — defining where text may be broken across lines — began as UTR #14 and was promoted to UAX #14 as it became essential infrastructure.

UTR #50 — Unicode Vertical Text Layout Defines the Vertical_Orientation property used by CSS writing-mode and other vertical layout implementations for East Asian text.

How UTRs Differ from UAXes

UTRs often serve as the research and development stage for features that may eventually become normative UAXes. When the community achieves consensus on an algorithm or property, it may be promoted to a UAX and bundled with the Unicode Standard release.

Finding UTRs

All current UTRs are published at https://www.unicode.org/reports/ alongside UAXes and Unicode Technical Standards (UTSes). Each document lists its current status, revision history, and whether it has been superseded.

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