context-budget

Context Budget — Token Estimation

Estimate how many tokens a file or directory will consume before reading it.

How to Estimate

Rule of thumb: 1 token ≈ 4 characters (English text/code). This is a rough estimate.

When the user asks about a file or directory:

1. Get the file size in bytes using:

wc -c < "filepath"

Or for a directory:

find "dirpath" -type f -exec wc -c {} + | tail -1

2. Estimate tokens: file_size_bytes / 4

3. Show the estimate with context AND model comparison:

File: path/to/file.py
Size: 12,400 bytes
Est. tokens: ~3,100
Context impact: 0.3% of 1M window

Cost to read (first time / cached):
  Opus:   $0.047 / $0.005
  Sonnet: $0.009 / $0.001
  Haiku:  $0.002 / $0.0002

Use these prices per 1M tokens for the comparison:

Model	Input	Cache Read	Cache Write	Output
Opus 4.6	$5.00	$0.50	$6.25	$25.00
Sonnet 4.6	$3.00	$0.30	$3.75	$15.00
Haiku 4.5	$1.00	$0.10	$1.25	$5.00

• "First time" = input price (first read, not yet cached)
• "Cached" = cache read price (subsequent reads in same session)
• Always show all three models so users can compare

For directories, also show file count and breakdown of largest files.

Context Impact Table

Tokens	% of 1M	% of 200K	Verdict
< 1K	0.1%	0.5%	Trivial
1-5K	0.1-0.5%	0.5-2.5%	Light
5-20K	0.5-2%	2.5-10%	Moderate
20-50K	2-5%	10-25%	Heavy — consider reading specific sections
50K+	5%+	25%+	Very heavy — read only what you need

Tips

• Suggest --offset and --limit on Read for large files
• For directories, suggest reading only the files that matter
• Minified JS/CSS files are token-dense — warn about them
• Binary files waste tokens — flag them