Tool Output Compression

Tool Output Compression

PromptPilot can compress noisy tool output before it reaches the coding agent.

The target is low-value repetition: long pytest traces, grep floods, installer progress logs, verbose diffs, and linter output. Compression is only valid when important debugging facts survive.

What to preserve

Compressed output should keep:

• The command that ran.
• Exit status or error code.
• Failing test names.
• Exception names and messages.
• Relevant file paths and symbols.
• The most useful stack frames.
• User constraints and non-goals.

What can usually shrink

• Repeated stack frames.
• Duplicate grep matches.
• Long progress bars.
• Repeated dependency install logs.
• Large unchanged diff context.

Claude Code setup

Add a PostToolUse hook for Bash output in your project-level .claude/settings.json or global ~/.claude/settings.json.

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "python <path-to-PromptPilot>/.codex/hooks/compress_tool_output.py",
            "timeout": 10,
            "statusMessage": "Compressing tool output..."
          }
        ]
      }
    ]
  }
}

Replace <path-to-PromptPilot> with the absolute path to this checkout if the target project is not the PromptPilot repository.

Codex setup

When running Codex inside the PromptPilot checkout, Codex picks up .codex/hooks.json automatically. The relevant entry calls:

python .codex/hooks/compress_tool_output.py

For another repository, copy or adapt the PostToolUse block from PromptPilot's .codex/hooks.json, and make the command point to the compression script location that exists in that project.

Review compression results

Use:

prpt stats --last 10

Compression telemetry is recorded so you can audit what changed and whether the savings are worth it.

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See also: Semantic Preservation · Telemetry and Replay · Benchmarks