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CRUX-Compress: Skill for Cursor

.cursor/skills/crux-utils/SKILL.md

crux-utils is a skill for Cursor from zotoio/CRUX-Compress. It costs 40 tokens per session (855 once invoked), scanned A, original, MIT.

A utility for CRUX, a workflow that compresses source files into shorter representations. It estimates tokens, compares file sizes, and calculates checksums, which are values used to track whether a file changed.

In plain words
What is it for?
Use it to estimate a file's token count, compare a source file with its compressed CRUX version, and create a source checksum.
Why use it?
It helps measure how much a file was shortened and provides a repeatable way to verify the source file being tracked.

Skill for Cursor

Written for Cursor: installed under .cursor/.

This is zotoio/CRUX-Compress's own configuration. It tells Cursor how to work on CRUX-Compress itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything CRUX-Compress configures →

not rated 8repo 14d ago A scan SkillSpector: pass 40 tokens original MIT
View source ↗ zotoio/CRUX-Compress compress.md
Reuse

Borrowing it

Nothing to install: this file belongs to zotoio/CRUX-Compress. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/zotoio/CRUX-Compress/main/.cursor/skills/crux-utils/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/zotoio/CRUX-Compress

Made for: Cursor.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

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README.md
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Your own site · 80×15
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Per session 40 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 855 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00040 $0.00855
Opus 5.5 $0.00016 $0.00342
Sonnet 5.5 $0.00008 $0.00171
Haiku 4.5 $0.00004 $0.00085

Measured 2mo ago against content hash e14528591106, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

crux-utils scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/crux-utils.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/skills/crux-utils/SKILL.md · 112 lines

How it starts

The opening of the file, as written. The whole thing — 112 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CRUX Utils

Multi-purpose utility for CRUX compression workflows. Provides deterministic tools for token estimation and checksum calculation.

Quick Start

# Token count estimation
python3 .cursor/skills/crux/crux-utils/scripts/crux-utils.py --token-count <file>

# Compare source vs CRUX (ratio mode, default target 25%)
python3 .cursor/skills/crux/crux-utils/scripts/crux-utils.py --token-count --ratio <source> <crux>

# Compare with custom target (e.g. 40%)
python3 .cursor/skills/crux/crux-utils/scripts/crux-utils.py --token-count --ratio <source> <crux> --target 40

# Get checksum for sourceChecksum frontmatter
python3 .cursor/skills/crux/crux-utils/scripts/crux-utils.py --cksum <file>

Modes

--token-count <file>

Estimate token count for a single file.

Output:

=== Token Estimate: example.md ===
Prose tokens:      397
Code tokens:       0
Special tokens:    0
---
TOTAL TOKENS:      397

--token-count --ratio <source> <crux> [--target <n>]

Compare source file vs CRUX file and calculate compression ratio.

The --target option sets the compression target percentage (1-100). Defaults to 25 if omitted, matching the CRUX spec's recommended target for text/code content.

Output:

=== Compression Ratio Analysis ===

=== Token Estimate: source.md ===
...
=== Token Estimate: source.crux.md ===
...

=== Compression Summary ===
Source tokens:     397
CRUX tokens:       140
Ratio:             35.2% of original
Reduction:         64.8%
Target (≤25%):     NO

--cksum <file>

Get checksum of a file, formatted for CRUX frontmatter sourceChecksum field.

Output:

=== Checksum: example.md ===
Checksum:          1234567890
---
FRONTMATTER:       "1234567890"

Token Estimation Method

Content Type Chars/Token Notes
Prose (markdown) 4.0 English text, headers, lists
Code blocks 3.5 More symbols, shorter identifiers
Special chars 1.0 CRUX Unicode symbols

Read the full file on GitHub · 112 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2mo ago First seen · 112 lines · 40 tokens per session scan A e14528591106

Subscribe to this mod's changes

crux-utils is a skill published in the GitHub repository zotoio/CRUX-Compress (8 stars, last pushed 14d ago), licensed MIT. It adds 40 tokens to every session and 855 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

claudecompressioncursormarkdownoptimisationrules
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