Skill Feedback: nimblebrain-contributor + build-mcpb (Stripe server build)

[JoeCardoso13]

Session Summary

Built a complete Stripe MCP server (mcp-stripe) using the nimblebrain-contributor skill for onboarding/contribution workflow and the build-mcpb skill for server implementation. Final outcome: working server with 14 tools across 7 Stripe resources, 27 passing tests, published to JoeCardoso13/mcp-stripe.

Platform: WSL2 (Ubuntu) on Windows, Python 3.13, FastMCP 2.14+

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nimblebrain-contributor Feedback

Step 1 — Environment Setup ⚠️ Friction

ty>=0.1.0 does not exist. The install table and pyproject.toml template pin ty>=0.1.0, but the latest release on PyPI is 0.0.17. uv sync --dev fails:

× No solution found when resolving dependencies:
╰─▶ Because only ty<=0.0.17 is available and mcp-stripe:dev depends on
    ty>=0.1.0, we can conclude that mcp-stripe:dev's requirements are
    unsatisfiable.

Suggested fix: Change constraint to "ty>=0.0.17" (or just "ty") in the template pyproject.toml and the install table.

Steps 2–3 — CLAUDE.md & Architecture ✅ Worked

No issues. Clear and well-structured.

Step 4 — Pick Work ⚠️ Friction

--label "integration" fails when label doesn't exist on the repo:

gh issue create ... --label "integration"
→ could not add label: 'integration' not found

Suggested fix: Either pre-create the label in the HQ repo, or remove --label from the skill instructions and let maintainers triage.

Step 5 — Get Started ❌ Broke

gh repo create --template fails for non-org-members:

gh repo create NimbleBrainInc/mcp-stripe \
  --template NimbleBrainInc/mcp-server-template --public --clone
→ GraphQL: JoeCardoso13 does not have the correct permissions to execute
  `CloneTemplateRepository`

Creating under personal account (JoeCardoso13/mcp-stripe) worked for the repo creation, but the bundled --clone step still failed (see below).

Suggested fix: The skill should guide a fork-based workflow for external contributors: create under personal namespace, then open a PR back to the org.

gh repo clone fails due to missing git-remote-https on WSL:

gh repo clone JoeCardoso13/mcp-stripe
→ git: 'remote-https' is not a git command. See 'git --help'.
  failed to run git: exit status 128

Plain git clone https://... worked as a fallback. This is a WSL-specific git packaging issue, but the skill could note the fallback.

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build-mcpb Feedback

Phase 1 — Discover ✅ Worked

API analysis phase worked smoothly.

Phase 2 — Scaffold ⚠️ Friction

Skill assumes scaffolding from scratch, but the template repo already has a directory structure. Could clarify the "rename/adapt existing template" path vs. creating from scratch.

Phase 3 — Implement ⚠️ Friction

Template api_client.py assumes JSON request bodies (Content-Type: application/json, json=data in aiohttp). Stripe uses application/x-www-form-urlencoded for all POST requests. We had to deviate from the template pattern.

Suggested fix: Add a note in the skill that API body encoding varies by provider, and the template's JSON default should be adapted when the target API uses form-encoded, XML, GraphQL, etc.

Phase 4 — Verify ❌ Broke (two issues)

1. ty>=0.1.0 in pyproject.toml template — same issue as nimblebrain-contributor Step 1 above.

2. FastMCP 2.14+ wraps @mcp.tool() as FunctionTool objects — the test template pattern of importing and calling tool functions directly breaks:

from mcp_stripe.server import list_customers
result = await list_customers(limit=10)
→ TypeError: 'FunctionTool' object is not callable

The decorated names are FunctionTool instances, not the original async functions. Tests must either:

• Call .fn on the tool object: await list_customers.fn(limit=10)
• Test the underlying client methods directly (what we did)

Suggested fix: Update the test template to account for FastMCP 2.x wrapping behavior. Recommend testing client logic directly rather than calling tool-decorated functions.

Phase 5 — Validate ❌ Broke

mcpb build and mpak-scanner are not available locally:

npx mcpb --version
→ npm error 404 Not Found - GET https://registry.npmjs.org/mcpb - Not found

mpak scanner scan
→ error: unknown command 'scanner'

These tools only exist in CI (via NimbleBrainInc/mcpb-pack@v2 GitHub Action).

Suggested fix: Clarify in the skill that Phase 5 packaging validation happens in CI. Provide the local alternative for runtime validation: programmatic tools/list check via the MCP tool manager.

Phase 6–7 — Document & Ship ✅ Worked

No issues with documentation or PR preparation.

Makefile Template ⚠️ Friction (cross-cutting)

sed -i '' is macOS/BSD syntax — breaks on GNU/Linux:

# Template has:
@sed -i '' 's/^version = .*/version = "$(VERSION)"/' pyproject.toml
# GNU sed treats '' as a filename → sed: can't read : No such file or directory

Suggested fix: Use sed -i (no empty string) for GNU, or detect OS:

SED_INPLACE := $(shell if sed --version 2>/dev/null | grep -q GNU; then echo "sed -i"; else echo "sed -i ''"; fi)

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Summary Table

Area	Item	Status
contributor Step 1	ty>=0.1.0 version	⚠️ Friction
contributor Step 4	--label "integration"	⚠️ Friction
contributor Step 5	--template for non-members	❌ Broke
contributor Step 5	git-remote-https on WSL	⚠️ Friction
build-mcpb Phase 2	Scaffold vs. existing template	⚠️ Friction
build-mcpb Phase 3	JSON vs form-encoded bodies	⚠️ Friction
build-mcpb Phase 4	ty>=0.1.0 constraint	❌ Broke
build-mcpb Phase 4	FastMCP FunctionTool wrapping	❌ Broke
build-mcpb Phase 5	mcpb/mpak-scanner local availability	❌ Broke
build-mcpb Makefile	sed -i '' on Linux	⚠️ Friction