BC safe-shell-execution
Use this skill whenever an AI agent is about to execute shell commands, run bash/zsh scripts, invoke system operations, or process user-provided command strings. Provides layered safety checks — injection pattern detection, destructive operation warnings, and sensitive file protection — derived from production security engineering in Claude Code. Trigger even for "simple" commands: the most dangerous injections often hide in seemingly innocent inputs. If a user asks you to run any command, execute a script, or use a shell tool, this skill applies.
As a process C 53/100 · Has gaps — weak spots: result and completion, inputs and preconditions, consistency
What is at stake
The skill contains fragments that, in the wrong hands, cost money or data. Below: what the installer risks and what the author should do.
The skill contains commands that delete files, rewrite disks or execute code fetched from the network. The agent may run them without asking if it believes the instructions require it.
Replace destructive commands with safe equivalents that ask for confirmation, scope them to one folder, and stop piping curl into a shell: pin a version and a checksum.
How to improve
- Address the high-severity findings: each costs 18 safety points. If one is a false positive, add the rule id to guard.allow in spec.yaml.
- Your own cases (evals/evals.json, 4–6 real requests with expected answers): the full check would then run those instead of a model-drafted suite.
- A spec.yaml with trigger phrases and assertions — a behaviour contract for CI; `skilltest init` writes a template.
Guard findings · 2
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high Dangerous commands
cmd-destructive-fsSKILL.md:69Destructive filesystem command (wipes root/home/drive) (documentation of a security skill)rm -rf / rm -fr / rm -r -f / rm -f -r → "May recursively force-delete files"
security skill
Medium and low: 1
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medium Dangerous commands
cmd-persistenceSKILL.md:96Persistence mechanism (cron / launchd / scheduled task / autorun registry) (documentation of a security skill)/etc/passwd /etc/hosts /etc/sudoers /etc/crontab
security skill
Files scanned: 2. Evidence is masked. Grey chips explain why severity was lowered.
Against the Agent Skills spec
- warning
frontmatter-yamlSKILL.md: the frontmatter is not valid YAML (YAML parse error: Nested mappings are not allowed in compact mappings at line 2, column 14: description: Use this skill whenever an AI agent is about to execute shell comm… ^ ); fields were read line by line. The usual cause is a colon inside an unquoted value
Process rating: all ten parameters 53/100
- 0Result and completion. Does not say what the result is
- 0Inputs and preconditions. Does not say what the process needs to start
- 30Running it twice. 1 mutating operations with no state check
- 40Consistency. Frontmatter name (safe-shell-execution) differs from the folder (safe-shell-execution-claude-code)
- 60Tools and files. Uses tools (bash, web) that frontmatter does not declare
- 60Failures and branches. 2 branches
- 70When it triggers. States when to use, but not when not to
- 100Steps. 10 steps
- 100Execution cost. Instruction body is 1505 tokens
- 100Progress reporting. Reports progress
Everything here is measured from the skill text rather than judged by a model, so the numbers are checkable. A parameter weighs more when it is a more common reason for the process to stall.
Quality signals
- +5Description has no quoted example phrases that should trigger the skill
- +4Description does not say when NOT to use the skill (false activations)
- +3Output format is not stated: the model decides each time
- +1No license
- +2Single-language instructions
- +3Description length 553: enough signal without eating the budget
- +4Structure: 13 headings
- +3Step-by-step instructions: 10 items
- +4Has examples (4 code blocks)
Quality base 70; lint remarks subtract, signals add up to 100. Result: 74.