Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add oborchers/fractional-cto --skill markdown-compressiongit clone --depth 1 https://github.com/oborchers/fractional-ctoWrote 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.
[](https://agentmods.dev/skills/oborchers/fractional-cto/markdown-compression)<a href="https://agentmods.dev/skills/oborchers/fractional-cto/markdown-compression"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/markdown-compression/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/oborchers/fractional-cto/markdown-compression"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/markdown-compression.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00100 | $0.01592 |
| Opus 5.5 | $0.00040 | $0.00637 |
| Sonnet 5.5 | $0.00020 | $0.00318 |
| Haiku 4.5 | $0.00010 | $0.00159 |
Grade A, and why
markdown-compression 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 1mo ago.
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.
How it starts
The opening of the file, as written. The whole thing — 127 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Markdown Compression
Markdown compression reduces token consumption in LLM-facing documentation — agent instructions, CLAUDE.md files, ARCHITECTURE.md files, system prompts, and skill definitions — while preserving the information an LLM needs to operate correctly.
Two modes address different risk tolerances:
| Mode | What Changes | Risk | Best For |
|---|---|---|---|
| Lossless | Structure only — whitespace, formatting, redundant syntax | Zero semantic change | Safe first pass on any file |
| Lossy | Semantics — rewriting for density, removing filler, consolidating | Information loss possible | Deep compression with review |
Section-by-section compression with user approval at each step is the recommended workflow. The /markdown-compressor:compress command provides a guided session; the skill also activates when compression-related work is detected mid-conversation.
Core Principle: What LLMs Actually Need
LLM instructions are not prose for humans. Compression targets what LLMs ignore or process redundantly:
Always safe to remove:
- Motivational filler ("This is important because...", "Remember to always...")
- Restated information (same rule in introduction and body)
- Hedging language ("You might want to consider...", "It's generally a good idea to...")
- Verbose transitions ("Now that we've covered X, let's move on to Y")
- Excessive examples when one suffices (keep the most distinctive example)
- Markdown decoration that adds no semantic value (unnecessary horizontal rules, decorative headers)
- HTML comments
- Redundant emphasis (bold + caps + exclamation mark conveying the same weight as bold alone)
Never remove:
- Specific values, thresholds, and constraints (numbers, limits, exact names)
- Behavioral rules and prohibitions ("NEVER do X", "ALWAYS do Y")
- Tool names, file paths, API endpoints, and identifiers
- Decision logic and conditional branches ("If X then Y, otherwise Z")
- Output format specifications
- Edge case handling instructions
- Cross-references to other files or systems
- YAML frontmatter (preserve exactly as-is)
What ships with it
4 files 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.
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.
- 1mo ago First seen · 127 lines · 100 tokens per session scan A 321a15f0e26c
markdown-compression is a skill published in the GitHub repository oborchers/fractional-cto (32 stars, last pushed 5d ago), licensed MIT. It adds 100 tokens to every session and 1,592 once invoked, about $0.0004 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 2026-08-30.
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