Krometrail

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Using Krometrail with OpenAI Codex ​

Krometrail gives Codex runtime debugging via MCP or the CLI — the same tools, two interfaces.

Add to your Codex config at ~/.codex/config.toml (global) or .codex/config.toml (per-project):

toml
[mcp_servers.krometrail]
command = "krometrail"
args = ["--mcp"]

Or add via the CLI:

bash
codex mcp add krometrail -- krometrail --mcp

Codex discovers the debug_*, chrome_*, and session_* tools automatically.

Focused tool sets ​

bash
# Debug tools only
codex mcp add krometrail-debug -- krometrail --mcp --tools=debug

# Browser tools only
codex mcp add krometrail-browser -- krometrail --mcp --tools=browser

Setup: CLI with Skill ​

For CLI-based usage, install the krometrail skill:

bash
npx skills add nklisch/krometrail --skill krometrail-debug krometrail-chrome

Example Workflow ​

Ask Codex:

The calculate_discount function returns wrong values for gold tier customers. Debug it.

Codex will:

  1. debug_launch (or krometrail debug launch) with python3 -m pytest tests/ -k test_gold and a breakpoint at discount.py:42
  2. Continue to the breakpoint
  3. Evaluate tier and tier_multipliers['gold']
  4. Step into the function
  5. Identify the bug and explain it

Tips ​

  • MCP is zero-config — Codex discovers tools automatically from the server
  • CLI path is transparent and scriptable — Codex can run multiple commands in parallel via bash
  • Session persistence — sessions are managed by a background daemon across multiple turns
  • Multiple sessions — use --session <id> to target a specific session when multiple are active

Verifying Setup ​

bash
krometrail doctor

This checks which language adapters are installed.