mcp.build

mcp.build is a community to build open source MCPs (Model Context Protocol servers) that adopted the Hal9 open source agent structure for its ease of use for deployment and interoperability.

Website: hal9ai.github.io/mcp.build (GitHub Pages from /docs)

This repo is structured so coding agents (Claude Code, Grok Build, Cursor, Codex, …) can contribute with minimal guesswork. Start at AGENTS.md and docs/llms.txt.

Why Hal9 agents?

Hal9 agents are intentionally simple: read from stdin with input(), write to stdout with print(). No framework lock-in. That shape maps cleanly to how MCPs expose tools to models, and makes agents easy to:

• Develop — plain Python, any library
• Deploy — hal9 deploy or GitHub Actions to hal9.com
• Interoperate — same agent can run as a chatbot, an API, or an MCP tool

Agents

Agent	Description	Path
send-email	Send emails with Resend from natural language prompts (Groq tool use)	send-email/

send-email

Example prompt:

send email to javier@hal9.ai with text hello!

The agent:

1. Reads the prompt via input()
2. Calls a Groq model with a send_email tool definition
3. Maps the tool call to the Resend API
4. Prints the result via print()

Environment variables

Variable	Required	Description
GROQ_API_KEY	Yes	API key from console.groq.com
RESEND_API_KEY	Yes	API key from resend.com
RESEND_FROM	No	Sender address (default: mcp.build <onboarding@resend.dev>)
GROQ_MODEL	No	Model id (default: llama-3.3-70b-versatile)

Local run

cd send-email
pip install -r requirements.txt
export GROQ_API_KEY=...
export RESEND_API_KEY=...
echo "send email to you@example.com with text hello!" | python app.py

Deploy to Hal9

export HAL9_TOKEN=...   # from https://hal9.com/devs
hal9 deploy send-email --name send-email --access public \
  --title "Send Email" \
  --description "Send emails via Resend using natural language prompts"

On push to main, if files under send-email/ change, .github/workflows/send-email.yaml deploys a new version to Hal9 (same pattern as hal9ai/hal9 app deploy workflows). Set the HAL9_TOKEN repository secret in GitHub Actions.

Website (GitHub Pages)

Static site lives in docs/ — no build step.

Path	Role
docs/index.html	Landing page
docs/css/styles.css	Styles
docs/agents.json	Machine-readable agent catalog
docs/llms.txt	Short instructions for LLMs / agents
AGENTS.md	Full rules for coding agents

Enable Pages: repo Settings → Pages → Build and deployment → Source: Deploy from a branch → Branch: main → Folder: /docs.

Contributing

Full checklist: AGENTS.md.

1. Add a new folder at the repo root with at least app.py.
2. Prefer input() / print() (or any stdin/stdout) so the agent stays Hal9- and MCP-friendly.
3. Add a requirements.txt if you need third-party packages.
4. Optionally add hal9.yaml for a welcome message.
5. Add a GitHub Actions workflow that deploys when that folder changes, following the send-email pattern.
6. Register the agent in docs/agents.json and mention it here.

License

Contributions are welcome. Individual agents may carry their own licenses; see each folder for details.