Check characters and numbers in an ASCII code table
Search standard ASCII 0–127 in the Browser and look up each radix, name, and Escape notation from a single character or a number with a specified radix. Input values are not sent to or stored on the DevelopTools Server.
Look up ASCII codes from charactersConclusion: Determine the character, numeric value, and input radix first
A is 65 and 0x41, a is 97 and 0x61, and 0 is 48 and 0x30. The current tool targets a single character and does not batch-convert multiple characters.
“あ” is outside the ASCII range, and the current tool does not automatically fall back to a Unicode value.
Look up representative characters from the character
| Input | decimal | hexadecimal | binary |
|---|---|---|---|
| A | 65 | 0x41 | 0b01000001 |
| a | 97 | 0x61 | 0b01100001 |
| 0 | 48 | 0x30 | 0b00110000 |
| ! | 33 | 0x21 | 0b00100001 |
| \ | 92 | 0x5C | 0b01011100 |
Specify the input format and prefix, then reverse-look up the value.
| Input | Auto-detect | When a format is specified |
|---|---|---|
| 65 | Decimal 65 → A | Parse as decimal |
| 0x41 | Hexadecimal 0x41 → A | Allow hexadecimal with or without 0x. |
| 41 | Decimal 41 → ) | Selecting hexadecimal gives 0x41 → A. |
| 0o101 | Octal 0o101 → A | Allow octal with or without 0o. |
| 0b01000001 | Binary → A | Allow binary with or without 0b. |
| U+0041 | Unicode notation → A | Allow Unicode notation with or without U+ |
| A | Single character → 65 | Parse as text |
| AB / 128 / あ | invalid | Cannot be interpreted as ASCII 0–127 |
Do not infer that prefixless 41 is hex. If the radix used by the protocol or log is known, switch the input format to hexadecimal, octal, or binary before investigating.
Supported scope of the current ASCII table and character-code reverse lookup tool
| Actions | Features | Current boundary |
|---|---|---|
| List | The 128 standard ASCII entries from 0 to 127 | Do not publish code page tables for 128–255. |
| Display | Character, decimal, hexadecimal, octal, binary, Unicode, abbreviation, name, description, category | Check UTF-8 byte sequences and Unicode name searches with the Unicode Tool |
| Reverse lookup | Single character, decimal, 0x, 0o, 0b, U+ format | Batch decomposition of multiple characters is not supported. |
| Input format | Explicitly select automatic, text, decimal, hexadecimal, octal, binary, or Unicode | Treat prefixless numbers detected automatically as decimal |
| search | Character, each radix, abbreviation, English name, Japanese description | Regular expression search and code page switching are not supported |
| Category | Control characters, printable characters, digits, uppercase English letters, lowercase English letters, symbols | Include DEL in the control-character group in the UI |
| Copy | Actual characters, each radix, Unicode, language-specific escapes, and HTML entities | Actual control characters may cause invisible behavior at the paste destination |
If the input is outside the ASCII range, such as “あ” or 128, the current tool displays “Cannot interpret as ASCII 0–127.” There is no fallback that automatically displays Unicode code points.
Treat standard ASCII as 7-bit values from 0 to 127.
| Range | classification | example |
|---|---|---|
| 0〜31 | Control characters, format effectors, and similar characters | NUL, BEL, HT, LF, CR, ESC |
| 32 | SPACE | Usually whitespace with no glyph |
| 33〜126 | printable characters | Symbols, digits, A–Z, and a–z |
| 127 | DEL | Non-printing. Note that RFC 20 states it is not strictly a control character. |
| 128〜255 | Outside the standard ASCII range | Characters cannot be determined without specifying the code page |
"Extended ASCII" is not a single standard. Assignments for the upper 128 values differ among Windows-1252, CP437, ISO-8859-1, and others, so do not determine a character from a number alone.
Read the same code position in decimal, hexadecimal, octal, and binary.
| characters | decimal | hexadecimal | octal | binary | Unicode |
|---|---|---|---|---|---|
| A | 65 | 0x41 | 0o101 | 0b01000001 | U+0041 |
| a | 97 | 0x61 | 0o141 | 0b01100001 | U+0061 |
| 0 | 48 | 0x30 | 0o060 | 0b00110000 | U+0030 |
| SPACE | 32 | 0x20 | 0o040 | 0b00100000 | U+0020 |
These are not different character encodings; they are values that represent the same integer in different bases. The current tool table zero-pads hexadecimal to two digits, octal to three digits, and binary to eight digits, and adds 0x, 0o, and 0b when copying.
Check control characters using visible labels and escape notation
| Name | decimal | hexadecimal | Representative escapes | A guide to the meaning |
|---|---|---|---|---|
| NUL | 0 | 00 | \0 | Null. Used for C string termination and similar purposes. |
| BEL | 7 | 07 | \a | Caution |
| BS | 8 | 08 | \b | Backspace |
| HT / TAB | 9 | 09 | \t | Horizontal Tab |
| LF | 10 | 0A | \n | Line Feed |
| FF | 12 | 0C | \f | Form Feed |
| CR | 13 | 0D | \r | Carriage Return |
| ESC | 27 | 1B | Such as \x1B | Escape |
| DEL | 127 | 7F | Such as \x7F | Delete and non-printable characters |
The current tool does not place NUL, TAB, LF, CR, ESC, SPACE, DEL, and similar characters directly in the character field; it visualizes them with name labels. Copying the actual character and copying escape notation have different meanings.
The "\n" shown on screen consists of two characters: backslash and n. An actual LF is one control character, and is different data for copying, comparison, and hashing.
Separate ASCII, Unicode code points, and UTF-8 byte sequences.
| characters | ASCII | Unicode Code Point | UTF-8 |
|---|---|---|---|
| A | 65 / 0x41 | U+0041 | 41 |
| \ | 92 / 0x5C | U+005C | 5C |
| あ | out of range | U+3042 | E3 81 82 |
| 😀 | out of range | U+1F600 | F0 9F 98 80 |
Unicode assigns Code Points to characters, while UTF-8 encodes those Code Points into byte sequences. The ASCII range has the same layout as Unicode U+0000–U+007F, and its one-byte UTF-8 values match, but they cannot be treated as identical outside ASCII.
The "Unicode" column in the current ASCII tool shows U+ notation corresponding to ASCII characters. Use the Unicode code table tool for UTF-8 and UTF-16 analysis or normalization of arbitrary Unicode characters.
Do not assume program API return values are ASCII-only
| environment | example | Exact meaning |
|---|---|---|
| Python | ord("A") → 65 | One Unicode code point for one character. It matches the ASCII value within the ASCII range. |
| Python | chr(65) → "A" | Return a character from a Unicode Code Point |
| JavaScript | "A".charCodeAt(0) → 65 | The UTF-16 code unit at the specified position |
| JavaScript | "😀".codePointAt(0) | Get the first Unicode code point |
| C | printf("%d", 'A') | Character constant value. 65 in common ASCII-compatible environments. |
| C | '\0' and '0' | NUL 0 and digit zero 48 are different values. |
For ASCII letters, A and a differ by 32, but do not generalize this rule to case conversion across all Unicode. In implementation, check each language's case conversion API and locale requirements.
Process input values in the browser.
The current ASCII tool performs search, reverse lookup, and copy-value generation with JavaScript in the browser. It does not send search values or selected characters externally through fetch or sendBeacon, and only stores the Light/Dark theme setting in LocalStorage.
- ASCII Master references fixed data for 0–127 generated in the repository.
- Search compares characters, radix representations, abbreviations, names, and descriptions in the browser.
- Write to the clipboard only when the user performs a copy action.
- Because actual control characters can change behavior at the paste destination, copy the code or escape instead when necessary.
Use related tools according to the meaning of the value
- Convert only numbers among binary, octal, decimal, and hexadecimal
- Investigate non-ASCII characters and Unicode code points.
- Compare LF / CRLF and string differences
- Check percent encoding such as %20.
- Convert strings and files to Base64.
The ASCII tool checks the correspondence between codes and characters. Check arbitrary integer base conversion, searches across all Unicode, difference comparison, URL encoding, and Base64 encoding as separate operations.
Check names and API meanings using primary sources
- RFC 20: ASCII format for Network Interchange
- Unicode: C0 Controls and Basic Latin
- Unicode: Latin-1 Supplement（U+00A5 YEN SIGN）
- Python: Built-in Functions ord()
- Python: Built-in Functions chr()
- ECMAScript: String.prototype.charCodeAt()
- ECMAScript: String.prototype.codePointAt()
- Microsoft Learn: doNotLeaveBackslashAlone
Prioritize RFC 20 and Unicode Basic Latin for ASCII ranges and names, official Unicode sources for Unicode characters, and official specifications for Python and JavaScript APIs. "Current tool" in the article refers to the implementation scope verified in the repository.
Summary
- Reverse-look up one character at a time.
- Check values using A, a, 0, and symbols.
- Do not assign arbitrary byte values to non-ASCII characters.
By checking not only displayed characters but also range, input radix, code points, byte sequences, and escape notation separately, you can isolate issues without confusing ASCII reverse lookup with character-encoding problems.
Example: Check how to look up an ASCII code from a character
Without changing the original string or log, isolate the one character or numeric value you want to inspect. If the radix is unknown, first check prefixes such as 0x and 0b and the notation in the specification.
Use the ASCII tool to check corresponding characters, names, and bases. If outside ASCII, switch to investigating Unicode or the original encoding.
- Check the value you want to investigate and whether it is text, decimal, hexadecimal, octal, or binary.
- Enter only one item in the character or code field, then auto-detect or explicitly specify the input format.
- Compare the reverse-lookup character, Decimal, Hex, Octal, Binary, Unicode, and name.
- For control characters, check the visible label and escape notation, and copy the actual character only when necessary.
- If outside 0–127, check with a code page or Unicode tool and do not confirm it as an ASCII value.
To read a value correctly, retain these three details: the radix, whether it is standard ASCII, and whether it is a code point or byte sequence.
Frequently asked questions
- Isn't ASCII 0–255?
- Standard ASCII is 7-bit, from 0 to 127. Assignments for 128–255 vary by Code Page, such as Windows-1252 and CP437, so they cannot be defined as a single ASCII table.
- Can Japanese and Emoji also be converted to ASCII codes?
- No. It is outside the ASCII range. Separate Unicode Code Points from Encoding such as UTF-8, and check with a Unicode code table Tool.
- Are search values and copied content sent to or stored externally?
- The current Tool performs search, reverse lookup, and copied-value generation in the Browser. It does not send input values with fetch or sendBeacon, and it does not store search history in LocalStorage.