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/fallback-code-executionnpx skills add HKUDS/OpenSpace --skill fallback-code-executiongit 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 | $0.00019 | $0.00645 |
| Opus 5 | $0.00010 | $0.00322 |
| Sonnet 5 | $0.00004 | $0.00129 |
| Haiku 4.5 | $0.00002 | $0.00064 |
Grade A, and why
fallback-code-execution 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 — 72 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Fallback Code Execution Workflow
Overview
This skill defines a robust workaround for executing code (specifically Python) when the primary execute_code_sandbox tool fails repeatedly with unknown or transient errors. Instead of continuing to retry the failing tool, the agent switches to a manual file-write and shell-execution pattern.
Trigger Conditions
Activate this workflow when:
execute_code_sandboxfails 2 or more times consecutively for the same logic.- Error messages are generic, unknown, or indicate environment issues rather than syntax errors.
- The code logic itself is verified correct but the execution environment is unstable.
Procedure
Step 1: Write Script to File
Use the write_file tool to save the Python script to a specific path in the workspace.
- Path: Choose a descriptive name ending in
.py(e.g.,scripts/generate_report.py). - Content: Ensure the script includes necessary error handling and print statements for debugging.
- Dependencies: If the script requires external libraries, ensure a
requirements.txtis updated or installed via shell beforehand.
Example:
tool: write_file
path: workspace/scripts/process_data.py
content: |
import sys
# ... script logic ...
print("Success")
Step 2: Execute via Shell
Use the run_shell tool to execute the script using the system Python interpreter.
- Command:
python3 <path_to_script>orpython <path_to_script>. - Working Directory: Ensure the shell command runs from the workspace root or the directory containing the script.
- Capture Output: Store stdout and stderr for verification.
Example:
tool: run_shell
command: python3 scripts/process_data.py
Step 3: Verify Execution
- Check Exit Code: Ensure the shell command returned exit code
0. - Check Output: Verify expected files were created or expected stdout messages appeared.
- Handle Errors: If the shell execution fails, inspect the stderr output. This often provides more detailed tracebacks than the sandbox tool.
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 · 72 lines · 19 tokens per session scan A 5c05b68b15d1
fallback-code-execution is a skill published in the GitHub repository HKUDS/OpenSpace (7,479 stars, last pushed 19d ago), licensed MIT. It adds 19 tokens to every session and 645 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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