Quick Start

Download a binary

# macOS (Homebrew)
brew install heptau/tap/pgarachne

# or download the latest release for your OS:
#   https://github.com/heptau/pgarachne/releases/latest

Create a database, the service role PgArachne connects as, and load the PgArachne schema (sql/schema.sql is in the repository):

createdb my_database
psql -d my_database -c "CREATE ROLE pgarachne LOGIN PASSWORD 'pgarachne_password'"
psql -d my_database -f sql/schema.sql

Create a pgarachne.env file (the server finds it in the current directory). STATIC_FILES_PATH lets PgArachne serve the web page you create in step 5 as well, so the page and the API share one origin and no CORS setup is needed:

DB_HOST=localhost
DB_PORT=5432
DB_USER=pgarachne
DB_SSLMODE=disable                         # local PostgreSQL without TLS only
STATIC_FILES_PATH=/path/to/web             # folder with your index.html
# Optional: enables JWT sessions (POST /db//token); generate with openssl rand -hex 32
# JWT_SECRET=…

Start the server (the service role’s password is read from PGPASSWORD or ~/.pgpass):

PGPASSWORD=pgarachne_password ./pgarachne

Every API method is a PostgreSQL function with a single jsonb argument. Create a role for the web page and the function; the JSON object a client sends as params arrives as payload:

CREATE ROLE demo_user WITH LOGIN PASSWORD 'user_password';
GRANT USAGE ON SCHEMA api TO demo_user;

CREATE OR REPLACE FUNCTION api.hello_world(payload jsonb DEFAULT '{}'::jsonb)
RETURNS json LANGUAGE sql AS $$
    SELECT json_build_object(
        'message', 'Hello, ' || COALESCE(payload->>'name', 'World') || '!');
$$;
GRANT EXECUTE ON FUNCTION api.hello_world(jsonb) TO demo_user;

Access is controlled by PostgreSQL itself: demo_user can call exactly the functions it was granted EXECUTE on — nothing else is reachable.

Your API endpoint is live. The user name and password of the PostgreSQL role are sent with HTTP Basic authentication:

curl -X POST http://localhost:8080/db/my_database/jsonrpc \
  -u demo_user:user_password \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"api.hello_world","params":{"name":"Alice"},"id":1}'
# → {"jsonrpc":"2.0","result":{"message":"Hello, Alice!"},"id":1}

The same call from a browser, with the built-in fetch(). Save this as index.html in the folder from STATIC_FILES_PATH and open http://localhost:8080/:

<input id="name" value="Alice">
<button id="hello">Say hello</button>
<pre id="out"></pre>

<script>
// HTTP Basic header: "user:password" in base64 (TextEncoder handles non-ASCII)
const bytes = new TextEncoder().encode("demo_user:user_password");
const auth = "Basic " + btoa(String.fromCharCode(...bytes));
const base = location.origin + "/db/my_database";      // /{API_PREFIX}/{database}

async function rpc(method, params) {
  const res = await fetch(base + "/jsonrpc", {
    method: "POST",
    headers: { "Authorization": auth, "Content-Type": "application/json" },
    body: JSON.stringify({ jsonrpc: "2.0", method, params, id: 1 }),
  });
  const body = await res.json();
  if (!res.ok || body.error) throw new Error(body.error.message);
  return body.result;
}

document.getElementById("hello").onclick = async () => {
  const result = await rpc("api.hello_world", { name: document.getElementById("name").value });
  document.getElementById("out").textContent = result.message;      // Hello, Alice!
};
</script>

PostgreSQL can publish messages with pg_notify; PgArachne forwards them to browsers as Server-Sent Events. Extend the function: when the caller passes "notify": true, it also publishes the greeting on the channel hello:

CREATE OR REPLACE FUNCTION api.hello_world(payload jsonb DEFAULT '{}'::jsonb)
RETURNS json LANGUAGE plpgsql AS $$
DECLARE
    greeting text := 'Hello, ' || COALESCE(payload->>'name', 'World') || '!';
BEGIN
    IF COALESCE((payload->>'notify')::boolean, false) THEN
        PERFORM pg_notify('hello', json_build_object('message', greeting)::text);
    END IF;
    RETURN json_build_object('message', greeting);
END; $$;

In the page, subscribe first, then call the function. The built-in EventSource cannot send an Authorization header, so the stream is read with fetch() (about 15 lines):

async function listen(channels, onMessage) {
  const res = await fetch(base + "/sse?channels=" + encodeURIComponent(channels), {
    headers: { "Authorization": auth },
  });
  if (!res.ok) throw new Error((await res.json()).error);
  const reader = res.body.getReader(), decoder = new TextDecoder();
  let buffer = "";
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    buffer += decoder.decode(value, { stream: true });
    let end;
    while ((end = buffer.indexOf("\n\n")) >= 0) {        // an event ends with a blank line
      const event = buffer.slice(0, end);
      buffer = buffer.slice(end + 2);
      for (const line of event.split("\n"))
        if (line.startsWith("data: ")) onMessage(JSON.parse(line.slice(6)));
    }
  }
}

listen("hello", (m) => console.log("event:", m.data.message));   // m = {channel, data}
rpc("api.hello_world", { name: "Alice", notify: true });             // the event arrives immediately

A function that returns rows (path, content, mime_type, store_only) can be downloaded through the /file endpoint — as raw bytes, without base64 inside JSON. This one returns hello-world.md:

CREATE OR REPLACE FUNCTION api.hello_world_file(payload jsonb DEFAULT '{}'::jsonb)
RETURNS TABLE (path text, content bytea, mime_type text, store_only boolean)
LANGUAGE sql AS $$
    SELECT 'hello-world.md',
           convert_to('# Hello, ' || COALESCE(payload->>'name', 'World') || E'!\n\nGenerated by PostgreSQL at ' || now() || E'.\n', 'UTF8'),
           'text/markdown',
           false;
$$;
GRANT EXECUTE ON FUNCTION api.hello_world_file(jsonb) TO demo_user;

In the page you can show the content or offer it as a download (return more rows and you get a ZIP automatically):

async function getFile() {
  const res = await fetch(base + "/file", {
    method: "POST",
    headers: { "Authorization": auth, "Content-Type": "application/json" },
    body: JSON.stringify({ method: "api.hello_world_file", params: { name: "Alice" } }),
  });
  if (!res.ok) throw new Error((await res.json()).error.message);   // errors are JSON, never binary
  return res.blob();
}

// show it:
console.log(await (await getFile()).text());

// or download it:
const url = URL.createObjectURL(await getFile());
const a = Object.assign(document.createElement("a"), { href: url, download: "hello-world.md" });
document.body.appendChild(a); a.click(); a.remove();
URL.revokeObjectURL(url);

Try it with curl: curl -u demo_user:user_password -H "Content-Type: application/json" -d '{"method":"api.hello_world_file"}' http://localhost:8080/db/my_database/file -OJ. More in File Download.

Expose the same functions to Claude Desktop or Cursor as tools via the MCP endpoint:

POST http://localhost:8080/db/my_database/mcp

See MCP (Model Context Protocol) for full connection instructions.

Every exposed function is also described as an OpenAPI 3.1 document, filtered to what the authenticated caller may call:

curl http://localhost:8080/db/my_database/openapi.json \
  -u demo_user:user_password
# or as YAML: .../openapi.yaml

Import the URL directly into Swagger UI, Postman, or an OpenAPI code generator. Every method still runs through the single JSON-RPC endpoint from step 5 — see Architectural Decisions for why the spec lists a per-method path without a matching real route.