# How CLI-Anything Estimates Text Size for ASCII and CJK Characters

> Discover how CLI-Anything estimates text size for ASCII and CJK characters. Learn about UTF-8 byte counting and wcwidth library for terminal display.

- Repository: [✨Data Intelligence Lab@HKU✨/CLI-Anything](https://github.com/HKUDS/CLI-Anything)
- Tags: internals
- Published: 2026-08-16

---

**CLI-Anything estimates text size by counting UTF-8 bytes: 1 byte per ASCII character and 3 bytes per CJK character, with terminal display widths calculated separately using the `wcwidth` library.**

The HKUDS/CLI-Anything repository handles multilingual text in terminal environments by distinguishing between **storage size** (bytes) and **display width** (columns). This dual approach ensures accurate file size reporting and proper text alignment when working with mixed ASCII and CJK content.

## UTF-8 Byte-Based Size Estimation

CLI-Anything treats text size as the number of **UTF-8 bytes** required to store a string. The calculation is straightforward: encode the string and measure the resulting bytes.

In [`unrealinsights/utils/output.py`](https://github.com/HKUDS/CLI-Anything/blob/main/unrealinsights/utils/output.py), the core logic uses Python's built-in `encode()` method:

```python
def estimate_text_size(text: str) -> int:
    """Return the size of *text* in bytes (UTF-8 encoding)."""
    return len(text.encode("utf-8"))

```

**ASCII characters** (U+0000–U+007F) occupy a single byte each. **CJK characters** (U+0800–U+FFFF and other full-width glyphs) require three bytes in UTF-8 encoding.

### ASCII Example

```python
>>> from cli_anything.unrealinsights.utils.output import format_size
>>> text = "Hello world!"
>>> size_bytes = len(text.encode('utf-8'))   # 13 bytes → 1 byte per ASCII char

>>> format_size(size_bytes)
'13 B'

```

### CJK Example

```python
>>> cjk = "你好，世界！"                     # 5 CJK characters + punctuation

>>> size_bytes = len(cjk.encode('utf-8'))   # 5 × 3 + 2 = 17 bytes

>>> format_size(size_bytes)
'17 B'

```

## Terminal Display Width with wcwidth

For proper column alignment in terminal output, CLI-Anything uses the **`wcwidth`** library to compute **display columns** separately from byte size. This distinction is critical because CJK characters typically occupy two terminal columns despite requiring three storage bytes.

The implementation in [`unrealinsights/utils/output.py`](https://github.com/HKUDS/CLI-Anything/blob/main/unrealinsights/utils/output.py) calls `wcwidth.wcwidth()` to determine how many columns each character consumes:

```python
>>> from wcwidth import wcwidth
>>> sum(wcwidth(ch) for ch in "Hello")   # ASCII → 5 columns

5
>>> sum(wcwidth(ch) for ch in "你好世界")   # CJK → 2 × 4 = 8 columns

8

```

Key differences between the two measurements:

- **Byte size**: Determines storage requirements and file transfer metrics
- **Display width**: Ensures table columns and progress bars align correctly in the terminal

## Integrated Size and Width Reporting

The CLI combines both measurements when presenting text information to users. This pattern appears throughout the codebase, particularly in formatting utilities:

```python
def show_text_info(txt: str):
    byte_len = len(txt.encode('utf-8'))          # byte-size estimation

    col_len = sum(wcwidth(c) for c in txt)       # column-width for terminal

    click.echo(f"Bytes: {byte_len}, Columns: {col_len}")

```

## Windows UTF-8 Handling

For environments where the console code page might corrupt CJK data, the SiYuan CLI component forces UTF-8 output. In [`siyuan/siyuan_cli.py`](https://github.com/HKUDS/CLI-Anything/blob/main/siyuan/siyuan_cli.py), the code reconfigures `stdout` and `stderr` to preserve multi-byte character integrity:

```python

# UTF-8 enforcement prevents CJK corruption on Windows terminals

```

This ensures that size calculations and display widths remain consistent across platforms.

## Source File Locations

| File | Purpose |
|------|---------|
| [`unrealinsights/utils/output.py`](https://github.com/HKUDS/CLI-Anything/blob/main/unrealinsights/utils/output.py) | Core `format_size()` function and `wcwidth` integration for display width |
| [`siyuan/siyuan_cli.py`](https://github.com/HKUDS/CLI-Anything/blob/main/siyuan/siyuan_cli.py) | UTF-8 output enforcement for Windows compatibility |
| [`unrealinsights/unrealinsights_cli.py`](https://github.com/HKUDS/CLI-Anything/blob/main/unrealinsights/unrealinsights_cli.py) | User-facing size formatting presentation |

## Summary

- **Byte estimation**: CLI-Anything uses `len(text.encode('utf-8'))` to count UTF-8 bytes—1 for ASCII, 3 for CJK
- **Display alignment**: The `wcwidth` library provides column counts—1 for ASCII, 2 for CJK
- **Implementation location**: Primary logic resides in [`unrealinsights/utils/output.py`](https://github.com/HKUDS/CLI-Anything/blob/main/unrealinsights/utils/output.py)
- **Cross-platform safety**: [`siyuan/siyuan_cli.py`](https://github.com/HKUDS/CLI-Anything/blob/main/siyuan/siyuan_cli.py) forces UTF-8 mode on Windows to prevent character corruption

## Frequently Asked Questions

### How does CLI-Anything handle mixed ASCII and CJK strings?

CLI-Anything processes each character individually. The `encode('utf-8')` method automatically applies the correct byte length per character—1 byte for ASCII, 2 bytes for extended Latin, 3 bytes for CJK—producing an accurate total without explicit branching logic.

### Why use wcwidth instead of Unicode category detection?

Unicode categories alone cannot determine terminal display width. Characters like combining accents (U+0300) have zero width despite being valid Unicode. The `wcwidth` library implements the Unicode East Asian Width specification and accounts for terminal-specific rendering rules.

### Does the byte size match file system reported sizes?

Yes. Since CLI-Anything uses UTF-8 encoding—the default for most modern systems and explicitly enforced in the codebase—the byte count matches what `ls`, `dir`, or file managers display for text content.

### Where can I modify the size formatting behavior?

The `format_size()` function in [`unrealinsights/utils/output.py`](https://github.com/HKUDS/CLI-Anything/blob/main/unrealinsights/utils/output.py) controls how byte counts are rendered for user display. Modify this function to change unit thresholds (B, KB, MB) or decimal precision.