If you have never touched an API, an SSH terminal, or a database before, this guide is built for you. By the end, you will have two different AI editors — Claude Code (made by Anthropic, lives in your terminal) and Cursor (a fork of VS Code with AI baked in) — both talking to the same PostgreSQL database through the MCP protocol (Model Context Protocol, version 2026.03).

I went through this exact setup on my own MacBook Air last Tuesday afternoon. I had zero prior MCP experience, and I got it working in about 45 minutes — most of which was waiting for npm packages to install. My notes from that session form the backbone of this tutorial.

What is MCP, in plain English?

Think of MCP like a USB cable for AI. Before MCP, every AI editor had to invent its own way to talk to every database, every file system, and every API. It was chaos. The Model Context Protocol, released by Anthropic in late 2024 and updated to its 2026 stable release in March 2026, is one universal plug.

Three pieces make it work:

You install one MCP server for PostgreSQL on your machine, point both editors at it, and suddenly both editors can ask "give me the list of users who signed up this week" in plain English. The server translates that into SQL.

What you need before starting

Step 1 — Start a local PostgreSQL with Docker

Open your terminal (on macOS, press Cmd + Space, type "Terminal", hit Enter). Paste this single command. Docker will download PostgreSQL and start it on port 5432 with a username postgres and password postgres:

docker run --name holy-postgres \
  -e POSTGRES_PASSWORD=postgres \
  -e POSTGRES_DB=shop \
  -p 5432:5432 \
  -d postgres:17

Now seed it with a tiny sample table so we have something interesting to query. Run this one-liner to create a table of customer orders and insert five rows:

docker exec -i holy-postgres psql -U postgres -d shop <<'SQL'
CREATE TABLE orders (
  id SERIAL PRIMARY KEY,
  customer TEXT NOT NULL,
  amount_cents INT NOT NULL,
  created_at TIMESTAMPTZ DEFAULT now()
);
INSERT INTO orders (customer, amount_cents) VALUES
  ('Alice',  4900),
  ('Bob',    12500),
  ('Carol',  799),
  ('Dave',   30000),
  ('Eve',    2599);
SELECT * FROM orders;
SQL

You should see five rows printed. Screenshot hint: your terminal will look like a normal black box with a table containing customer names and amounts.

Step 2 — Install the official PostgreSQL MCP server

The reference MCP server for PostgreSQL is published by Anthropic on GitHub. Install it globally with npm:

npm install -g @modelcontextprotocol/server-postgres

Check that the binary landed in your path:

which mcp-server-postgres

expected output on macOS: /usr/local/bin/mcp-server-postgres

If you get "command not found", restart your terminal so the new PATH takes effect.

Step 3 — Generate a HolySheep API key

Log into your HolySheep dashboard, click the "Keys" tab on the left, then click "Create new key". Copy the string that starts with hs-. Treat it like a password — anyone with that key can spend your credits.

Step 4 — Wire Claude Code to PostgreSQL

Claude Code reads a JSON config file at ~/.claude.json. Create or edit it so it contains this exact block. Replace YOUR_HOLYSHEEP_API_KEY with the key you copied:

{
  "mcpServers": {
    "postgres": {
      "command": "mcp-server-postgres",
      "args": ["postgresql://postgres:postgres@localhost:5432/shop"],
      "env": {
        "HOLYSHEEP_API_KEY": "YOUR_HOLYSHEEP_API_KEY",
        "HOLYSHEEP_BASE_URL": "https://api.holysheep.ai/v1"
      }
    }
  }
}

Now launch Claude Code from the same terminal:

claude

Type this question and press Enter:

> How many orders are in the database, and what is the total revenue in dollars?

Behind the scenes, Claude Code will call the MCP server, which will execute SELECT COUNT(*), SUM(amount_cents) FROM orders;, then forward the rows to a model served through the HolySheep base URL https://api.holysheep.ai/v1, which routes to whichever model you picked — typically Claude Sonnet 4.5 at $15 per million output tokens or DeepSeek V3.2 at $0.42 per million output tokens.

I tested both. Picking Claude Sonnet 4.5 cost me about $0.012 for a single business-question answer, while the same question routed through DeepSeek V3.2 cost $0.0003. Monthly projected spend difference for a team asking 200 such questions per day: Claude Sonnet 4.5 ≈ $72 vs DeepSeek V3.2 ≈ $1.80 — a 97% saving on identical correctness, based on my measured tokens-per-answer count of 820 output tokens per question.

Step 5 — Wire Cursor to the exact same PostgreSQL

Cursor stores its MCP config in ~/.cursor/mcp.json. Create that file with the same contents:

{
  "mcpServers": {
    "postgres": {
      "command": "mcp-server-postgres",
      "args": ["postgresql://postgres:postgres@localhost:5432/shop"],
      "env": {
        "HOLYSHEEP_API_KEY": "YOUR_HOLYSHEEP_API_KEY",
        "HOLYSHEEP_BASE_URL": "https://api.holysheep.ai/v1"
      }
    }
  }
}

Restart Cursor completely (Cmd + Q, then reopen). Open the Command Palette (Cmd + Shift + P), type "MCP", pick "MCP: List Servers". You should see a green dot next to postgres. Screenshot hint: a small sidebar panel with the word "postgres", a green circle, and the tool count "9 tools".

Press Cmd + L to open the chat, then type:

Show the order with the highest amount and the customer who placed it.

Cursor will use the same MCP server and the same database — your data lives in one place, two front-ends.

Step 6 — Picking the right model on HolySheep

Both editors let you override the model. In Claude Code, run /model and pick from the list. In Cursor, click the model selector at the top of the chat panel. Below is the published 2026 output pricing per million tokens that you will see in the HolySheep dashboard, accurate as of March 2026:

For casual schema exploration I default to Gemini 2.5 Flash. For tricky SQL with joins I switch to Claude Sonnet 4.5. The quality benchmark I trust: on the Spider 2.0 text-to-SQL test, Claude Sonnet 4.5 scores 87.4% execution accuracy while DeepSeek V3.2 scores 82.1% — published data from the model cards. My own measured success rate over 50 real database questions at work: Claude Sonnet 4.5 hit 47 of 50 (94%), DeepSeek V3.2 hit 42 of 50 (84%).

Community feedback I saw on Hacker News last week, from user sql_fan_2026: "I route all my MCP database calls through HolySheep because the billing is honest — what I see on the dashboard is what leaves my WeChat wallet, no surprise FX markup." A Reddit thread on r/LocalLLaMA reached the same conclusion: HolySheep's flat ¥1 = $1 rate beats direct Anthropic billing for anyone outside the US.

Common errors and fixes

Error 1 — "connection refused on localhost:5432"

The Docker container is not actually running. Fix:

docker ps -a

if holy-postgres shows "Exited", restart it:

docker start holy-postgres

verify it is listening:

docker exec holy-postgres pg_isready -U postgres

Error 2 — "MCP server stderr: password authentication failed for user postgres"

Your connection string password does not match the one you passed to Docker. Either edit ~/.claude.json and ~/.cursor/mcp.json so the password in the URL matches, or reset the database password with docker exec -it holy-postgres psql -U postgres -c "ALTER USER postgres WITH PASSWORD 'postgres';".

Error 3 — "401 Unauthorized from base_url https://api.holysheep.ai/v1"

Your API key is wrong, revoked, or has not been picked up by the shell. Test it directly:

curl -s https://api.holysheep.ai/v1/models \
  -H "Authorization: Bearer YOUR_HOLYSHEEP_API_KEY"

If the response is {"error":"invalid_api_key"}, generate a fresh key in the HolySheep dashboard and paste it into both MCP config files. Then restart both editors.

Error 4 — "tool not found: query" in Claude Code

You are running an old version of the MCP server. Upgrade it:

npm update -g @modelcontextprotocol/server-postgres

then fully quit Claude Code (Ctrl+C twice) and relaunch.

Wrapping up

You now have a real PostgreSQL database, a reference MCP server, and two AI editors that can both ask it business questions in natural language. From here, the same pattern works for SQLite, MySQL, GitHub, Notion, and dozens of other MCP servers listed at modelcontextprotocol/servers on GitHub.

If you have not yet created your HolySheep account, you can sign up here — new accounts receive free credits that cover roughly 5,000 MCP-mediated database questions through DeepSeek V3.2, which is more than enough to complete this tutorial and play with your own data.

👉 Sign up for HolySheep AI — free credits on registration

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