I turned a real OpenAPI into an MCP server in 5 min (without losing custom code on regen)

Description and use

The MCP generator now groups operations by tags, producing a manageable number of tools, supports filtering, incremental regeneration, and preserves custom code.

Problem

Generating an MCP server from a large OpenAPI spec produced too many tools (one per operation), making the server unusable.

Outcome

The generator now produces a manageable number of tools, supports selective generation, preserves custom code across regenerations, and offers improved language support and validation.

Workflow

• 1. Run generator with grouping: node dist/cli/index.js generate -i api.yaml -o ./out --group-by tag
• 2. Optionally filter by tags or paths: --include-tags pets --group-by tag or --path-prefix "/users/"
• 3. Add custom code between markers (// @@mcp-gen:start:… and // @@mcp-gen🔚…) to survive regeneration
• 4. Regenerate incrementally: node dist/cli/index.js generate -i api.yaml -o ./out --incremental
• 5. Validate spec: node dist/cli/index.js validate -i examples/petstore.yaml

Evidence

200 operations across 8 tags become ~8 tools. Each group routes internally by action.

Source

Your code lives between markers and survives regen with a 3‑way merge

Source