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/hkuds/openspace/code-execution-fallbacknpx skills add HKUDS/OpenSpace --skill code-execution-fallbackgit clone --depth 1 https://github.com/HKUDS/OpenSpaceWhat 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 | $0.00017 | $0.01014 |
| Opus 5 | $0.00009 | $0.00507 |
| Sonnet 5 | $0.00003 | $0.00203 |
| Haiku 4.5 | $0.00002 | $0.00101 |
Grade A, and why
code-execution-fallback 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 yesterday.
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 — 156 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Code Execution Fallback & Workspace Anchoring
This skill provides a robust pattern for executing code when the primary method fails, combined with proper workspace path management to prevent file location errors.
Core Techniques
1. Workspace Path Anchoring
Always establish and verify your working directory at the start of any task:
# At the beginning of any code execution
import os
workspace_path = os.getcwd()
print(f"Working directory: {workspace_path}")
# In shell scripts
pwd
echo "Current directory: $(pwd)"
Why: Prevents files from being written to unexpected locations when agents switch between tools.
2. Execution Fallback Ladder
When execute_code_sandbox fails, follow this escalation pattern:
Level 1: Retry with Simpler Code
- Simplify the code structure
- Remove complex dependencies
- Add explicit error handling
Level 2: Use run_shell with Heredoc
When sandbox execution repeatedly fails, switch to shell execution:
python3 << 'EOF'
import os
import pandas as pd
# Your code here
data = {"col1": [1, 2, 3], "col2": ["a", "b", "c"]}
df = pd.DataFrame(data)
df.to_csv("output.csv", index=False)
print("File written successfully")
EOF
Key points:
- Use
<< 'EOF'(quoted) to prevent variable expansion - Include all imports and dependencies inline
- Add explicit success/failure messages
Level 3: Delegate to shell_agent
For complex multi-step tasks with error recovery needs:
Task: Create a data processing pipeline that reads CSV, transforms data, and outputs Excel
Requirements:
- Handle missing values
- Apply transformations
- Write to ./output/ directory
- Retry on transient errors
3. Explicit Path Management
Always use absolute or explicitly relative paths:
# BAD - relies on implicit working directory
df.to_csv("output/data.csv")
# GOOD - explicit path anchoring
import os
base_path = os.getcwd()
output_dir = os.path.join(base_path, "output")
os.makedirs(output_dir, exist_ok=True)
df.to_csv(os.path.join(output_dir, "data.csv"))
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.
- yesterday First seen · 156 lines · 17 tokens per session scan A e7a7d0d684e3
code-execution-fallback is a skill published in the GitHub repository HKUDS/OpenSpace (7,479 stars, last pushed 19d ago), licensed MIT. It adds 17 tokens to every session and 1,014 once invoked, about $0.0001 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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