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 majiayu000/claude-skill-registry --skill 39-agent-skills-mcp-code-executiongit clone --depth 1 https://github.com/majiayu000/claude-skill-registryWrote 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/majiayu000/claude-skill-registry/39-agent-skills-mcp-code-execution)<a href="https://agentmods.dev/skills/majiayu000/claude-skill-registry/39-agent-skills-mcp-code-execution"><img src="https://agentmods.dev/badge/skills/majiayu000/claude-skill-registry/39-agent-skills-mcp-code-execution/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/majiayu000/claude-skill-registry/39-agent-skills-mcp-code-execution"><img src="https://agentmods.dev/badge/skills/majiayu000/claude-skill-registry/39-agent-skills-mcp-code-execution.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 3 findings, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Rogue Agent · line 34 Skill modifies its own code, configuration, or behavior at runtime. Self-modification enables an agent to escalate privileges, disable safety constraints, or install persistent backdoors.Fix: Prevent the skill from modifying its own code, SKILL.md, or configuration files. Treat skill files as read-only at runtime.
- high Output Handling · line 184 Model output is used without validation or sanitization. Unvalidated output injected into downstream contexts (SQL, shell, HTML) enables injection attacks and arbitrary code execution.Fix: Validate and sanitize all model output before using it in downstream contexts. Use parameterized queries for SQL, shell quoting for commands, and HTML encoding for web output.
- medium Excessive Agency · line 685 Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
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 | $0.00050 | $0.05253 |
| Opus 5 | $0.00025 | $0.02627 |
| Sonnet 5 | $0.00010 | $0.01051 |
| Haiku 4.5 | $0.00005 | $0.00525 |
Grade A, and why
39-agent-skills-mcp-code-execution scanned grade A with 1 finding 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 12d 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.
Runs shell commandslowCapability
Expected in a hook, worth knowing in a rule or an instructions file.
result = subprocess.run( How it starts
The opening of the file, as written. The whole thing — 698 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Build Script-Execution Skill
You've learned the pattern (Lesson 5): write code from specification → execute it → analyze errors → iterate. Now you're going to build a skill that orchestrates this loop autonomously.
But here's what makes this different from following a tutorial: You'll specify what problem you're solving FIRST, then let AI help you build the skill while you validate each decision. You're not just learning a pattern—you're learning to think about error recovery, convergence criteria, and edge cases the way production systems demand.
Step 1: Write Your Specification
Before touching any skill code, write a specification for the problem you're solving. You'll use a CSV data processing task because it's concrete and has natural edge cases.
Choose one of these:
- CSV Analysis: Analyze customer or sales data for patterns
- CSV Transformation: Clean and restructure messy CSV data
- CSV Aggregation: Group data by dimensions and calculate metrics
Or define your own data processing task.
Your Specification
Write this to a file (skill-spec.md) or document:
# CSV Analysis Skill Specification
## Intent
[What does this skill do? Be specific about the business problem it solves]
## Input
- data_file: [type and format, e.g., "CSV with columns: customer_id, purchase_date, amount"]
- parameters: [what configuration does skill accept?]
## Output
- format: [JSON, CSV, report?]
- required_fields: [exact fields that must be in output]
- validation_rules: [how to verify output is correct]
## Success Criteria
- All data processed without loss
- Output format exactly matches specification
- Edge cases handled gracefully (malformed rows, missing values, etc.)
- Execution completes within 30 seconds
## Edge Cases to Handle
- [Case 1: e.g., "Empty CSV file"]
- [Case 2: e.g., "Missing column header"]
- [Case 3: e.g., "Non-numeric values in amount field"]
Key principle: Your specification must be complete enough that AI can generate correct code without additional context. If your spec is vague, the generated code will be equally vague.
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.
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.
- 12d ago First seen · 698 lines · 50 tokens per session scan A 0a56a80568d1
39-agent-skills-mcp-code-execution is a skill published in the GitHub repository majiayu000/claude-skill-registry (600 stars, last pushed yesterday), licensed MIT. It adds 50 tokens to every session and 5,253 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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