sandbox-routing

name	Sandbox Routing
description	SELF-CORRECT tool choice. About to Read a long file just to extract one piece of info? Use a sandbox tool that returns only the summary. About to run a long shell command? Same. Sandbox keeps raw output OUT of context — only summaries land. Triggers when about to flood context with large output.

Sandbox Routing

[!danger] HARD RULE — fires before any large Read or Bash that isn't for editing If you're about to Read a long file to analyze (not to Edit), or run a Bash command with >20 line output, route through sandbox tools instead. Raw output stays out of context; only the summary you print enters context.

This skill assumes your Claude Code install includes context-mode (or equivalent) sandbox tools — ctx_execute, ctx_execute_file, ctx_batch_execute. If those aren't available, the principle still applies: use head_limit on Grep, narrow Read to specific line ranges, and avoid cat large.log.

The decision tree

Am I about to Read or run Bash?
   ├── Editing a file? (need full content for Edit tool)
   │     → Read is correct, proceed
   │
   ├── Running git status / git log -n short / mkdir / mv / rm / short command?
   │     → Bash is correct, proceed
   │
   ├── Reading a file just to extract a piece of info / find a line?
   │     → STOP. Use ctx_execute_file with grep/awk code that prints just the answer.
   │
   ├── Running a shell command with >20 line output?
   │     → STOP. Use ctx_execute with the same command — only printed summary enters context.
   │
   └── Multiple commands at once?
         → Use ctx_batch_execute with all commands as labelled chunks, indexed for FTS5 search.

When to use each tool

ctx_execute(language, code)

• Shell command with large output → language: "shell"
• Python data processing → language: "python"
• API calls + response analysis → wrap the call in code
• Anything where you want the answer, not the raw output

ctx_execute_file(path, language, code)

• File analysis without loading the file into context
• Searching within a specific known file
• Extracting structured info from JSON/YAML/MD

ctx_batch_execute(commands, queries)

• Multiple commands you want to run + index together
• Chained recon (e.g., git log + git diff + git status as one batch)
• Building a knowledge base for later FTS5 queries

Calibration anchors

File size	Read/Bash OK?	Sandbox?
<20 lines	✅ Read/Bash	not needed
20-100 lines	✅ if editing or referencing in full	✅ if extracting
100-500 lines	⚠️ only if editing	✅ for extraction
500+ lines	❌ unless absolutely editing	✅ always for extraction

Concrete examples

Example A: Find an insertion anchor in a 900-line JSON

• ❌ Wrong: Read skill-index.json (entire file) to find where to insert
• ✅ Right: ctx_execute_file path=skill-index.json code='grep -n "skill-name" skill-index.json' → returns just the line number, then use Edit

Example B: Check git log for a specific commit pattern

• ❌ Wrong: Bash: git log --oneline -100 (100 lines of log into context)
• ✅ Right: ctx_execute language=shell code='git log --oneline -100 | grep -i "ship"' → returns just matches

Example C: Read a large config file for one value

• ❌ Wrong: Read large-config.yaml
• ✅ Right: ctx_execute_file path=large-config.yaml code='grep "specific_key" large-config.yaml'

Output format

When this skill fires, internally evaluate before the tool call:

• Will the raw output be >20 lines AND I don't need it for editing?
• If yes → re-route to sandbox before invoking

You don't need to announce this to the principal. Just use the right tool.

Anti-patterns this prevents

• Reading a 900-line skill-index just to find an insertion anchor
• cat large.log via Bash to "see what's happening"
• Reading 50-page docs to extract one quote
• Running parallel Bash commands when a single batch call could do one round-trip
• The PreToolUse hooks firing reminders that get ignored as false positives

Connects to

• /timeline-calibration — sister discipline rule, both about respecting the resource budget