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mcpgen

Regenerate safely after editing

Regeneration is the normal way to apply config changes (transport, protocol, features, new specs). It is safe by construction: see the ownership model for the decision table. This page is the practical recipe.

Recipe

Section titled “Recipe”
Terminal window
# 1. Preview the plan. Writes nothing.
mcpgen new ./weather --force --dry-run --json


# 2. Apply. Only flags you pass override the existing mcpgen.json.
mcpgen new ./weather --transport http --force --no-check --json


# 3. Verify.
mcpgen check ./weather --json

The dry-run envelope contains plan.files[] with path, action (create / overwrite / skip), owner, and reason for every file. Real example after editing an mcpgen-owned file:

{ "path": "internal/mcpapp/instructions.go", "action": "skip", "owner": "mcpgen",
  "reason": "modified since generation (hash mismatch)" }
{ "path": "internal/mcpapp/tools/handlers/greet.go", "action": "skip", "owner": "user",
  "reason": "user-owned file already exists" }

What to expect

Section titled “What to expect”
  • Your handler code is never touched. User-owned files always skip.
  • mcpgen-owned files you edited also skip. The reason is modified since generation (hash mismatch). Your edit wins; regen does not overwrite it. If you want the fresh generated version, delete the file and regen, or revert your edit first.
  • Untracked files are never clobbered (exists and is not managed by mcpgen).
  • mcpgen.json and .mcpgen/manifest.json are always rewritten. Only explicitly passed flags override the existing config; everything else is preserved. --features is additive — remove a feature by editing mcpgen.json.
  • One nuance: the tidy stage of check runs go mod tidy, which can rewrite go.mod. After a check, go.mod often hashes differently than the manifest entry, so a later regen skips it with modified since generation (hash mismatch). This is expected and harmless — the file keeps the tidy result.

Restore a generated file

Section titled “Restore a generated file”

If you edited an mcpgen-owned file and want the generated version back:

Terminal window
rm weather/internal/mcpapp/instructions.go
mcpgen new ./weather --force --no-check --json   # recreates it (action: create)

Next steps

Section titled “Next steps”