About this tool
All 128 ASCII codes with their decimal, hexadecimal, octal and binary values, the escape sequence where one exists, and the HTML entity. Search accepts whatever you have: paste the character itself, type its name or abbreviation, or enter 65, 0x41, 101 or 01000001 — they all find the letter A.
The 33 control codes get a real explanation rather than a three-letter abbreviation, because they are the reason people look this table up. An unexpected byte in a file is almost always one of these: a NUL where a string was truncated, a stray CR from a Windows line ending, a form feed left in a source file, or the ESC that begins every terminal colour sequence. Each row says what the code was for and where it still turns up — including the ones you have met without knowing, like the DC3 that Ctrl+S sends to freeze a terminal.
Worth knowing what ASCII is not: it defines 128 characters and nothing above 127. A byte over 127 belongs to whatever encoding the file actually uses, which today is almost always UTF-8, where those bytes are part of a multi-byte sequence rather than characters in their own right. That distinction is behind most "why does my text look like é" questions.