Trace MCP Codemod

trace-mcp — Codemod Workflow

apply_codemod is the correct tool for any repeated mechanical change. Using Edit for the same pattern twice or more is a waste of tokens and is error-prone.

When to Use — HARD RULE

If you are about to make the same kind of change 2 or more times — whether in one file or across many — stop and use apply_codemod. This includes:

• Adding async/await to a set of functions
• Updating a function signature everywhere it is called
• Fixing import paths after a move
• Adding or removing keywords/decorators
• Wrapping calls in a logger, try/catch, or feature flag
• Replacing a deprecated API usage
• Any regex-replaceable refactor

No exceptions. "It's just three edits" is still a violation — use apply_codemod.

Standard Workflow

1. Preview with dry run (default)

apply_codemod({
  pattern: "oldFunction\\(",
  replacement: "newFunction(",
  file_pattern: "src/**/*.ts",
  dry_run: true        // default
})

Review the preview: matched files, context lines, and replacement correctness. Look for false positives.

2. Narrow scope when needed

Use filter_content to only touch files that also contain a second marker:

apply_codemod({
  pattern:        "extractNodes\\(",
  replacement:    "extractNodes(ctx, ",
  file_pattern:   "src/**/*.ts",
  filter_content: "import.*extractNodes",
  dry_run:        true
})

For patterns that cross line boundaries, enable multiline mode:

apply_codemod({
  pattern:     "function\\s+foo\\([^)]*\\)\\s*\\{",
  replacement: "async function foo() {",
  multiline:   true,
  dry_run:     true
})

3. Apply the change

apply_codemod({ ..., dry_run: false })

If more than 20 files are affected, add confirm_large: true.

4. Reindex and verify

• register_edit is not needed for codemods — apply_codemod handles reindexing internally.
• Run the test suite or check_quality_gates with scope: "changed".

Planning Larger Changes

For changes that span packages or require version awareness (e.g. upgrading a dependency), use plan_batch_change first:

plan_batch_change({
  package:      "lodash",
  from_version: "4.17.0",
  to_version:   "5.0.0"
})

This returns an impact report with all affected files and import references. Combine it with apply_codemod for the actual rewrite.

Anti-Patterns to Avoid

• Using Edit with replace_all for renames — use apply_rename (see trace-mcp-refactoring).
• Chaining 3–10 Edit calls with the same old_string pattern shape — use apply_codemod.
• Skipping the dry-run preview — always review matches first.
• Forgetting confirm_large: true on changes >20 files.