Stackin MCP plugin — NF-e and NFS-e for ChatGPT, Claude Code, Codex and Cursor

Issue, consult, correct and cancel Brazilian electronic invoices (nota fiscal eletrônica) from any AI client that speaks the Model Context Protocol.

Ask in plain language — "issue an NFS-e for this service", "why was my last NF-e rejected?", "cancel invoice 1042 and tell me the reason code" — and the model does it through Stackin, against SEFAZ and the municipal NFS-e webservices.

Sixteen tools, nine skills, one hosted server. No SDK to install, no XML to sign, no certificate to juggle in the client.

• 🧾 NF-e (goods) and NFS-e (services) — issue, consult, cancel
• 🔎 Diagnose a rejection by the tax authority's own code, and choose reissue vs. correction
• ✉️ Correction letter (CC-e) against an authorized NF-e
• 📥 Received invoices — read and manifest documents other companies issued against yours
• 🔢 Numbering invalidation for a reserved, never-used NF-e range
• 📄 DANFE / DANFSe PDF straight out of the conversation
• 🔎 Fiscal code lookup — resolve an NCM, CFOP or CEST instead of guessing one, and confirm who a CNPJ belongs to

Table of contents

• Install in Claude Code
• Install in ChatGPT and Codex
• Connect from Cursor or any MCP client
• Authentication: OAuth or API key
• Skills
• What is in this repository
• One plugin, three clients
• MCP Registry
• FAQ
• Maintainer notes

Install in Claude Code

The repository is its own marketplace, so it installs straight from GitHub:

claude plugin marketplace add stackin-io/stackin-mcp-plugin
claude plugin install stackin@stackin

The plugin brings the nine skills and points Claude Code at https://mcp.stackin.io/mcp. There is nothing to configure: the first tool call answers 401 with WWW-Authenticate, and Claude Code follows it — run /mcp in the session, authorize in the browser that opens, and the token is stored for you. The client registers itself through /oauth/register, so no client_id is handed out by anyone.

Prefer a static key? Add the server by hand with a header instead of installing the plugin — see Authentication.

Install in ChatGPT and Codex

The same server is published as a ChatGPT app over Developer Mode. Enable developer mode, register https://mcp.stackin.io/mcp as a connector, and authorize — the full walkthrough, with video, is at docs.stackin.io/mcp.

Connect from Cursor or any MCP client

Any MCP client can use the server directly, without this plugin. Cursor reads .cursor/mcp.json in the project, or ~/.cursor/mcp.json. The interpolation syntax is not the same as Claude Code's: Cursor wants ${env:VAR}.

{
  "mcpServers": {
    "stackin": {
      "url": "https://mcp.stackin.io/mcp",
      "headers": { "Authorization": "Bearer ${env:STACKIN_API_KEY}" }
    }
  }
}

Claude Code, by hand — ${VAR} expands from the environment:

claude mcp add --transport http stackin https://mcp.stackin.io/mcp \
  --header "Authorization: Bearer ${STACKIN_API_KEY}"

Authentication: OAuth or API key

Two ways in, and they behave differently.

An API key. Generate one at app.stackin.io; it already carries the environment, so there is nothing to choose in the client. Send it as Authorization: Bearer <key>.

OAuth, with no key at all. Leave the header out: a tool call answers 401 with WWW-Authenticate pointing at /.well-known/oauth-protected-resource, which is what makes Claude Code offer to log in when you run /mcp. The server supports dynamic client registration (/oauth/register), so a client that registers itself gets a client_id without anyone being asked. Cursor can also hold static client credentials under an auth key instead of registering dynamically.

Verified on 2026-09-09, up to the browser: the server connects with no header at all, a tool call answers 401 with the resource_metadata challenge, the protected-resource document resolves, /oauth/register returns 201 and /oauth/authorize redirects to the consent screen. The browser leg itself has not been walked from Claude Code or Cursor — ChatGPT completed a real consent, those two have not. If one stops midway, look at the redirect_uri it uses: /oauth/authorize only accepts a URI the client registered.

Skills

A skill exists only where the order of operations, or a fiscal rule, adds something a tool description cannot carry on its own.

What is in this repository

This repository is the distribution layer: the manifests, the skills and the assets. The server itself lives at https://mcp.stackin.io/mcp and speaks the Model Context Protocol.

One plugin, three clients

The repo carries three manifests because three ecosystems look in three places, and each one fails silently when its file is missing:

Adding the folder to Claude Code failed with "No marketplace manifest found … (expected .cursor-plugin/marketplace.json or .claude-plugin/marketplace.json)" until the third row existed. The skills are shared: all three point at skills/, so a skill written once is read by every client.

MCP Registry

server.json describes the hosted server for the official MCP Registry as a remote entry — io.github.stackin-io/stackin, streamable-http, no package to install.

Publishing is automated: pushing a v* tag runs .github/workflows/publish-mcp.yml, which stamps the version from the tag, authenticates with GitHub OIDC (no stored token — the workflow's own identity is what grants the io.github.stackin-io/* namespace) and publishes.

git tag v1.0.0 && git push origin v1.0.0

The registry lists the public repository, which is why the entry lives here and not beside the server's own source.

FAQ

Do I need a digital certificate (A1/A3) in the client? No. The certificate is uploaded once at app.stackin.io and stays server-side.

Does it work in production, or only homologation? Both. The environment is fixed on the API key, or on the connection you authorized over OAuth — there is nothing to pick per call.

Which municipalities are supported for NFS-e? The ones Stackin covers; consult docs.stackin.io. NF-e is nationwide through SEFAZ.

Can I use the server without this plugin? Yes — it is a plain MCP server. The plugin only adds the skills and saves you the manual configuration.

Is it free? Issuing consumes credits from your Stackin account. Consulting and cancelling do not.