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 skills/pydantic/monty/python-playgroundnpx skills add pydantic/monty --skill python-playgroundgit clone --depth 1 https://github.com/pydantic/montyWhat 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 | $0.00044 | $0.00378 |
| Opus 5 | $0.00022 | $0.00189 |
| Sonnet 5 | $0.00009 | $0.00076 |
| Haiku 4.5 | $0.00004 | $0.00038 |
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.
What it actually says
Python Playground
Run Python code in an isolated playground directory for testing and experimentation.
Instructions
- First, ensure the playground directory exists. If the
playgrounddirectory doesn't already exist, runmkdir playground. - Use the Write tool to create the Python file at
playground/test.py - Run with:
uv run playground/test.pyto test cpython behavior orcargo run -- playground/test.pyto 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
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.
- 2d ago First seen · 51 lines · 44 tokens per session scan A 543d16ac8f2a
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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