python-playground

An isolated workspace for running and testing Python code without affecting the main project. It uses a dedicated playground directory and supports running scripts with uv or Monty.

In plain words
What is it for?
Use it to run Python scripts, test code snippets, investigate CPython behavior, or compare Python execution with Monty.
Why use it?
It provides a safer place to experiment with Python behavior, investigate errors, and test small examples before changing project code.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/pydantic/monty/python-playground
Any agent
npx skills add pydantic/monty --skill python-playground
Clone the repo
git clone --depth 1 https://github.com/pydantic/monty

Made for: Claude Code, Codex.

Per session 44 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 378 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00044 $0.00378
Opus 5 $0.00022 $0.00189
Sonnet 5 $0.00009 $0.00076
Haiku 4.5 $0.00004 $0.00038

Measured 2d ago against content hash 543d16ac8f2a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

python-playground 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 2d 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.

.agents/skills/python-playground/SKILL.md · 51 lines

What it actually says

Python Playground

Run Python code in an isolated playground directory for testing and experimentation.

Instructions

  1. First, ensure the playground directory exists. If the playground directory doesn't already exist, run mkdir playground.
  2. Use the Write tool to create the Python file at playground/test.py
  3. Run with: uv run playground/test.py to test cpython behavior or cargo run -- playground/test.py to test monty behavior

IMPORTANT: Use separate tool calls for each step - do NOT chain commands with &&. This allows the pre-approved commands to work without prompting.

Example workflow

Step 1 - Create directory if it doesn't already exist (Bash, already allowed):

mkdir playground

Step 2 - Write code (use Write tool, not cat): Write to playground/test.py:

def foo():
    raise ValueError('test')

foo()

Step 3 - Run script (Bash, already allowed):

uv run playground/test.py

Guidelines

  • The playground/ directory is gitignored
  • Use a different file name for each test you want to run, give the files recognizable names like test_value_error.py
  • Use uv run ... to run scripts (uses project Python)
  • Or, cargo run -- ... to run scripts using Monty
  • Use Write tool for creating files (avoids permission prompts)
  • Run mkdir and uv as separate commands (not chained)
  • do NOT delete files from playground after you've finished testing
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. 2d ago First seen · 51 lines · 44 tokens per session scan A 543d16ac8f2a

Subscribe to this mod's changes

python-playground is a skill published in the GitHub repository pydantic/monty (8,153 stars, last pushed today), licensed MIT. It adds 44 tokens to every session and 378 once invoked, about $0.0002 per session on Opus 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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