NFC (Canonical Composition)

NFC: The Web's Default Normal Form

NFC (Normalization Form C — Canonical Composition) is the most widely used Unicode normalization form. It works in two passes: first, it decomposes all characters into their canonical base + combining mark sequences (like NFD), then it recomposes them back into precomposed characters wherever the Unicode standard defines a canonical composition.

The result is the shortest canonical representation of a string. For most Latin-script text, NFC means characters like é, ü, and ñ are stored as single code points rather than two-code-point sequences. For text that is already in NFC (pure ASCII, for instance), normalization is a no-op.

Why NFC is the Recommended Default

The W3C mandates NFC for all web content in the Character Model for the World Wide Web. Most databases, APIs, and programming environments assume NFC. HTTP headers, JSON payloads, and HTML source files are all expected to use NFC.

macOS user-space applications generally use NFC (despite HFS+ using NFD internally — the OS translates at the file system boundary). Windows and Linux also default to NFC in most contexts. If you are writing text to a file, database, or API and you want maximum interoperability, NFC is the right choice.

Python Examples

import unicodedata

# e + combining acute → é (one code point)
decomposed = "e\u0301"      # NFD form: 2 code points
composed = unicodedata.normalize("NFC", decomposed)

print(repr(decomposed))     # 'e\u0301'
print(repr(composed))       # '\xe9'  (which is é, U+00E9)
print(len(decomposed))      # 2
print(len(composed))        # 1

# Normalize user input before storing
def store_text(text: str) -> str:
    return unicodedata.normalize("NFC", text)

# NFC is idempotent
s = "caf\u00e9"
assert unicodedata.normalize("NFC", s) == s
assert unicodedata.is_normalized("NFC", s)

NFC does NOT fold compatibility characters. The fi ligature fi (U+FB01) remains fi under NFC. For search and identifier normalization where you want fi == fi, use NFKC instead.

Quick Facts