OpenEnv is a framework for creating, deploying, and using isolated execution environments through simple APIs modeled on Gymnasium. It is intended for researchers and developers training agents with reinforcement learning, as well as creators who need secure environments that can be deployed and accessed through familiar protocols. The catalogue add-ons provide agent integrations and workflows for using OpenEnv.
Borrowing it
Nothing to install: this file belongs to huggingface/OpenEnv. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/huggingface/OpenEnv/main/.claude/skills/write-tests/SKILL.mdgit clone --depth 1 https://github.com/huggingface/OpenEnvWrote 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/huggingface/openenv/write-tests)<a href="https://agentmods.dev/skills/huggingface/openenv/write-tests"><img src="https://agentmods.dev/badge/skills/huggingface/openenv/write-tests/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/huggingface/openenv/write-tests"><img src="https://agentmods.dev/badge/skills/huggingface/openenv/write-tests.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00017 | $0.00487 |
| Opus 5.5 | $0.00007 | $0.00195 |
| Sonnet 5.5 | $0.00003 | $0.00097 |
| Haiku 4.5 | $0.00002 | $0.00049 |
Grade A, and why
write-tests 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 — 86 lines — stays where its author put it; the contents beside it link to each section on GitHub.
/write-tests
Write failing tests that encode acceptance criteria.
Usage
/write-tests
/write-tests Add logout button to header
When to Use
- After creating a todo that requires implementation
- Before running
/implement - When you have clear acceptance criteria
When NOT to Use
- Implementation already exists (tests would pass immediately)
- You're exploring or prototyping (not TDD mode)
- Just adding to existing test coverage
What It Does
- Analyzes the current todo/requirement
- Reads existing tests to understand patterns
- Writes test files that verify acceptance criteria
- Verifies tests FAIL (proves they test something real)
- Returns test file paths for
/implement
Output
The tester agent will produce:
## Tests Written
### Files Created/Modified
- `tests/test_client.py`
### Tests Added
| Test | Verifies |
|------|----------|
| `test_client_reset_returns_observation` | Reset returns valid observation |
| `test_client_step_advances_state` | Step mutates state correctly |
| `test_client_handles_invalid_action` | Error handling for bad input |
### Verification
All tests FAIL as expected (no implementation yet).
### Next Step
Run `/implement` to make these tests pass.
Rules
- Read existing tests first to understand patterns and conventions
- Test behavior, not implementation - write from user's perspective
- Integration tests first, then unit tests if needed
- Each test verifies ONE thing clearly
- Run tests to verify they fail before returning
Anti-patterns (NEVER do these)
- Writing tests that pass without implementation
- Testing implementation details instead of behavior
- Writing overly complex test setups
- Adding implementation code (that's
/implement's job) - Writing tests that duplicate existing coverage
Completion Criteria
Before returning, verify:
- Tests compile/run successfully (pytest can collect them)
- Tests FAIL (no implementation yet)
- Test names clearly describe what they verify
- Tests follow existing project patterns (see
tests/for examples)
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 · 86 lines · 17 tokens per session scan A e5904765dff7
write-tests is a skill published in the GitHub repository huggingface/OpenEnv (2,739 stars, last pushed 8d ago), licensed BSD-3-Clause. It adds 17 tokens to every session and 487 once invoked, about $0.0001 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 2026-08-31.
Other skills, from other repositories
engram-testing-coverage
TDD and coverage standards for Engram. Trigger: When implementing behavior changes in any package.
principle-test-behavior-not-implementation
Apply when you write, change, or keep a test. Assert what the code's users can observe, so that the test fails when that behavior breaks and keeps passing when only the internals change.
conductor-implement
Execute tasks from a track's implementation plan following TDD workflow.
tdd
This skill should be used when the user wants to implement features or fix bugs using test-driven development. Enforces the RED-GREEN-REFACTOR cycle with vertical slicing, context isolation between test writing and implementation, human checkpoints, and auto-test feedback loops. Uses multi-agent orchestration with the…
mobiai-mobile-tdd
You MUST use this before writing any implementation code for a mobile feature, bug fix, refactor, or behavior change. Tests come before implementation — no exceptions.
iterative-development
TDD iteration loops using Claude Code Stop hooks - runs tests after each response, feeds failures back automatically.