Create MCP App

Create a Paid MCP App

SolvaPay-monetized MCP server on Cloudflare Workers. OpenAPI auto-generation or hand-written tools.

Human at a terminal? npm create solvapay@latest <name> -- --type mcp (use @latest). Ships from-openapi (one-to-one) and from-scratch modes, runs install + solvapay init in one pass.

Agent? scripts/describe.mjs + scripts/scaffold.mjs per references/from-openapi/guide.md. Intent-driven clustering and hand-tuned narration require an LLM — the CLI cannot author src/tools/*.ts. Internal dev runs use the same agent path with --dev and create-solvapay@preview.

Scope

This skill covers any MCP server whose tools return text or structuredContent — data, intelligence and analytics, search and retrieval, integrations with external APIs, actions and workflows, computations, content generation. Domain-agnostic.

The only UI this skill ships is SolvaPay's built-in checkout / account / topup widget, which mounts only when the user deliberately invokes the account viewer (slash prompts /upgrade, /manage_account, /topup remap onto it with the matching view). For custom graphical widgets, keep this skill for server + paywall wiring and add references/mcp-apps-ui.md.

Guardrails

• Never expose SOLVAPAY_SECRET_KEY to client code, public env vars, or deploy-time plaintext. Upload via npx wrangler secret put and keep it in a gitignored .env only for local dev.
• Never wrap SolvaPay intent tools (account, activate_plan) or the UI transport tools with payable.mcp() — they are the paywall recovery path, not paid business logic.
• Never set _meta.ui.resourceUri on merchant payable tools. Hosts MUST open the iframe on every advertised call (SEP-1865), which flashes an empty widget on silent successes.
• Never return custom iframe/UI on paywall gates — text-only narration naming `account` with the appropriate view (or `activate_plan` when a planRef is known).
• Always use mode: 'json-stateless' on stateless edge runtimes (Cloudflare Workers, Deno, Supabase Edge).
• Always hide UI-only virtual tools from text-only hosts with hideToolsByAudience: ['ui'].
• Always confirm the resolved SOLVAPAY_PRODUCT_REF after solvapay init; under --yes / non-TTY, never treat an auto-picked product as final until the user confirms it belongs to this MCP.
• If the requested business model is usage-based or metered, verify that the selected product has the intended usage-based plan before handoff. selections.plans[] is validated during scaffold but is not created by scaffold.
• Deploy-existing = scaffolding only. On "deploy my existing server" tasks, add only deploy scaffolding (scripts/deploy.mjs, wrangler.jsonc [vars], .env) and never open or edit src/worker.ts — not for imports, CORS, Env, the canonical template, or "stale API shape" patches. Note any API drift in the handoff as a follow-up. Exception: paywall-wiring tasks ("add SolvaPay paywall to my existing MCP server") do edit src/worker.ts — see references/existing-server.md.

Gotchas

• Deploy pre-flight: run npx wrangler whoami first (not just wrangler login) to confirm auth and print the *.workers.dev subdomain.
• @solvapay is not a valid package — use subpaths (@solvapay/mcp, @solvapay/mcp/fetch, etc.).
• ctx.registerPayable(name, config) takes exactly two arguments — not (toolDef, paymentConfig, handler).
• Paid handlers return c.respond(data, { text: narration }) — never raw content arrays from paid handlers.
• Run node scripts/describe.mjs against a local spec file — fetch URLs to /tmp/spec-*.json first; don't pass URLs directly.
• Binary/multipart operations must be skipped. After running describe.mjs, grep the original spec for multipart/form-data, application/octet-stream, image/, and application/pdf under requestBody.content and response content. For each matching operation (e.g. uploadFile, uploadImage), set tier: "skip" in selections.json — MCP tools return text, not file streams, so these can't be wrapped usefully.
• Empty or relative OpenAPI servers must be resolved before scaffold. Confirm the upstream base URL with the user, and watch for path-prefix outliers (e.g. /apifhir/... among /api/fhir/...) before generating tools.
• selections.json must live outside the scaffold target dir (e.g. /tmp/selections-<uuid>.json) — upstream API keys must not land in the project tree.
• Don't scaffold into an unrelated app repo root without confirming where the MCP worker should live — it's its own deployable unit.
• scripts/describe.mjs and scripts/scaffold.mjs in this skill are wrappers — see scripts/README.md for resolution order.

Mandatory read order

Before writing tool code:

1. This SKILL.md — routing, input mode, host.
2. references/tool-design.md — registerPayable shape, response contract.
3. One input-mode guide: references/from-openapi/guide.md or references/from-scratch/guide.md or references/existing-server.md.
4. If intent-driven mode (OpenAPI): also read references/from-openapi/intent-driven.md (G2/G3/G7 gate shapes) and references/from-openapi/scaffold.md (G6 gate, selections.json preview) before executing any gate.

Do not write registerPayable(...), additionalTools, or src/tools/* until all required files are loaded.

Confirmation level (G0 — ask once)

Before any other gate, ask how chatty you should be. See references/hitl-conventions.md.

"How chatty should I be? standard (default) confirms each big decision; auto only confirms irreversible steps (scaffold, deploy, go-live); chatty reviews every intent and file."

Routing

1. Existing paid-MCP project? All of: @solvapay/mcp or @solvapay/server in package.json, wrangler.jsonc, and src/worker.ts with createSolvaPayMcpFetch / createSolvaPayMcpServer → references/from-scratch/scaffold-and-extend.md. Do not scaffold.

2. Greenfield — ask once: "OpenAPI/Swagger spec, or hand-written tools?"

Inside an unrelated app repo: if cwd is a Next.js app, backend, or monorepo without a paid-MCP server in scope, stop and ask where the MCP server should live before scaffolding (sibling dir or apps/ / packages/ subdirectory).

Dev mode (internal testing only). Use preview tooling and append --dev when testing against api-dev: npm create solvapay@preview <name> -- --type mcp --dev, node scripts/describe.mjs --dev ..., node scripts/scaffold.mjs --dev ..., and npx -y solvapay@preview init --dev. Never for end users.

3. Host: default Cloudflare → references/hosting/cloudflare/README.md. Other hosts → references/hosting/alternatives.md. Optional custom MCP UI → references/mcp-apps-ui.md.

4. Credentials: after scaffold → references/solvapay-init.md (npx -y solvapay@latest init).

Human CLI shortcut (terminal only): see the human block at the top of this file.

OpenAPI flow & gates

describe.mjs → author selections.json → validate-selections.mjs (loop until pass) → scaffold.mjs <selections> <target-dir> → author tools per references/tool-design.md → solvapay init → confirm product/plan → verify → test → deploy. SOLVAPAY_SECRET_KEY is set by solvapay init, never in selections.json. Full G0–G9 HITL gates: references/hitl-conventions.md.

Scripts

Verification loop

1. Run the mode's validator (verify script, wrangler dev, or guide checklist).
2. On failure → mode-guide troubleshooting → fix → re-run until pass.
3. Only then complete the handoff template.

Handoff template

## MCP app handoff
- **Input mode:** from-openapi / from-scratch / existing-server
- **Host:** Cloudflare / alternative
- **Worker URL:** [url]
- **Tools authored:** [list]
- **Gates cleared:** G0–G[n]
- **Product ref:** [prd_... + how it was confirmed]
- **Plan / metering status:** [free default / usage-based plan verified / needs user action]
- **Sandbox:** [success path + gate path verified; note skipped checks explicitly]
- **Paid-path verification:** [paywallGate / merchantBootstrap / upstream smoke: passed, skipped, or not run]
- **Known gaps:** [if any]

Task progress

• Read references/tool-design.md + matching mode guide
• Route (existing vs greenfield, input mode, host)
• Complete mode guide (OpenAPI: describe → validate → scaffold → author)
• Run references/solvapay-init.md
• Run verification loop until pass
• Complete handoff template