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 agentmods add rules/johnpolacek/vibecode.party.starter/999-mdc-formatgit clone --depth 1 https://github.com/johnpolacek/vibecode.party.starterWrote 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/rules/johnpolacek/vibecode.party.starter/999-mdc-format)<a href="https://agentmods.dev/rules/johnpolacek/vibecode.party.starter/999-mdc-format"><img src="https://agentmods.dev/badge/rules/johnpolacek/vibecode.party.starter/999-mdc-format.svg" alt="Measured on agentmods" 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 | $0.00000 | $0.01026 |
| Opus 5 | $0.00000 | $0.00513 |
| Sonnet 5 | $0.00000 | $0.00205 |
| Haiku 4.5 | $0.00000 | $0.00103 |
Grade A, and why
999-mdc-format 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 5d 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 — 133 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MDC File Format Guide
MDC (Markdown Configuration) files are used by Cursor to provide context-specific instructions to AI assistants. This guide explains how to create and maintain these files properly.
File Structure
Each MDC file consists of two main parts:
- Frontmatter - Configuration metadata at the top of the file
- Markdown Content - The actual instructions in Markdown format
Frontmatter
The frontmatter must be the first thing in the file and must be enclosed between triple-dash lines (---). Configuration should be based on the intended behavior:
---
# Configure your rule based on desired behavior:
description: Brief description of what the rule does
globs: **/*.js, **/*.ts # Optional: Comma-separated list, not an array
alwaysApply: false # Set to true for global rules
---
Important: Despite the appearance, the frontmatter is not strictly YAML formatted. The
globsfield is a comma-separated list and should NOT include brackets[]or quotes".
Guidelines for Setting Fields
- description: Should be agent-friendly and clearly describe when the rule is relevant. Format as
<topic>: <details>for best results. - globs:
- If a rule is only relevant in very specific situations, leave globs empty so it's loaded only when applicable to the user request.
- If the only glob would match all files (like
**/*), leave it empty and setalwaysApply: trueinstead. - Otherwise, be as specific as possible with glob patterns to ensure rules are only applied with relevant files.
- alwaysApply: Use sparingly for truly global guidelines.
Glob Pattern Examples
- **/*.js - All JavaScript files
- src/**/*.jsx - All JSX files in the src directory
- /components//*.vue - All Vue files in any components directory
Markdown Content
After the frontmatter, the rest of the file should be valid Markdown:
# Title of Your Rule
## Section 1
- Guidelines and information
- Code examples
## Section 2
More detailed information...
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.
- 5d ago First seen · 133 lines · 1,026 tokens per session scan A 1878b373ee59
999-mdc-format is a cursor rule published in the GitHub repository johnpolacek/vibecode.party.starter (27 stars, last pushed 1y ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,026 tokens. 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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