[

Left square bracket

ASCII Code: 91•Category: brackets

The left square bracket ([) opens arrays in programming languages, initiates list structures in data formats, and provides alternative grouping in mathematical notation, making it essential for data organization and computational logic.

Technical Details

ASCII Code: 91
HTML Entity: [
Hexadecimal: 0x5B
Binary: 01011011
Octal: 133

Usage & Examples

Programming

char symbol = '['; // ASCII 91

HTML/Web

[ or [

Common Uses

bracketsquareopenarrayprogrammingindexingcitationlistmathematical

How to Type This Character

Windows

Alt Code:

Hold Alt and type91 on numeric keypad

Character Map:

Search "Character Map" in Start menu

Mac

Character Viewer:

Press Ctrl +Cmd +Space

Copy & Paste:

Easiest method - copy from this page!

💡 Pro tip: The fastest way is to bookmark this page or copy the character from our ASCII library!

Related Characters

About the Left square bracket

Array Foundation

Fundamental to array declaration and indexing in virtually all programming languages. Square brackets define lists, collections, and indexed data structures that form the backbone of software development, from simple variables to complex databases.

Data Structure Notation

Essential for JSON arrays, Python lists, JavaScript arrays, and database query syntax. Square brackets organize structured data that powers web applications, APIs, and modern software architecture.

Mathematical Alternatives

Provides alternative grouping to parentheses in mathematical expressions, particularly useful in complex formulas with multiple levels of nesting. Square brackets create visual hierarchy and improve readability in advanced mathematics.

Citation Systems

Used in some academic citation styles for bibliographic references, footnotes, and cross-references. Square brackets distinguish different types of citations and maintain scholarly formatting standards.

History of the Left square bracket

1600s

Mathematical Notation

Mathematicians began using square brackets as an alternative to parentheses for grouping complex expressions, providing visual distinction in nested mathematical formulas and algebraic notation.

1800s

Scientific Classification

Scientific publications adopted square brackets for editorial insertions, corrections, and clarifications in quoted material, establishing scholarly conventions for textual accuracy.

1950s

Programming Arrays

Early programming languages like FORTRAN introduced square bracket notation for array indexing, creating the computational convention that defines modern software development.

1990s

Web Technologies

HTML attributes, JSON arrays, and web programming made square brackets ubiquitous in internet technologies, powering everything from web forms to API responses.

2000s-Present

Data Science

Big data, machine learning, and data analysis tools made square bracket notation central to data manipulation, from pandas DataFrames to NumPy arrays in scientific computing.

Cultural Impact

The left square bracket became the opening symbol of structured data organization, enabling the complex information systems that power modern technology while maintaining mathematical precision in scientific computation.

Usage Examples

Programming Arrays

Example

let numbers = [1, 2, 3, 4, 5]; array[index]; myList[0]

Array declaration and element access in programming languages

JSON Data

Example

[{"name": "John", "age": 30}, {"name": "Jane", "age": 25}]

JSON array notation for web APIs and data interchange

Mathematical Notation

Example

f[x] = x² + 1, [a + b] × [c - d], interval [0, 1]

Alternative grouping and interval notation in mathematics

Editorial Citations

Example

"He [Lincoln] said the union must be preserved." [emphasis added]

Editorial insertions and clarifications in quoted text