diff --git a/package.json b/package.json
index 76c65f4..f4440c5 100644
--- a/package.json
+++ b/package.json
@@ -33,6 +33,7 @@
   },
   "dependencies": {
     "@alex.garcia/unofficial-observablehq-compiler": "0.6.0-alpha.9",
+    "@observablehq/prettier": "^2.2.1-alpha.1",
     "@observablehq/runtime": "4.9",
     "chalk": "^4.1.1",
     "chokidar": "^3.5.1",
diff --git a/src/dataflow b/src/dataflow
index 2a5fb8b..f316285 100755
--- a/src/dataflow
+++ b/src/dataflow
@@ -2,6 +2,7 @@
 const { program } = require("commander");
 const { compileNotebook } = require("./compile");
 const { runServer } = require("./run");
+const {format} = require("./format");
 
 function parseSecrets(values) {
   const secrets = new Map();
@@ -52,7 +53,7 @@ program
     });
   });
 
-program
+  program
   .command("run <notebook>")
   .description(
     "Start a server that runs the given Observable notebook (from a .ojs file)."
@@ -87,4 +88,18 @@ program
     });
   });
 
+  program
+  .command("format <notebook>")
+  .description(
+    "Format a notebook's source with the custom Prettier plugin."
+  )
+  .option(
+    "--write",
+    "Over-write the given file with the formatted source.",
+    false
+  )
+  .action((notebook, options) => {
+    format(notebook, options);
+  });
+
 program.parse(process.argv);
diff --git a/src/format.js b/src/format.js
new file mode 100644
index 0000000..f31d51b
--- /dev/null
+++ b/src/format.js
@@ -0,0 +1,73 @@
+const prettier = require("@observablehq/prettier");
+const {ModuleParser} = require("@observablehq/parser");
+const {readFileSync, writeFileSync} = require("rw").dash;
+
+// this was not fun to figure out :(
+function prettify(source) {
+  return prettier.format(source, 
+  {
+    parser: "dataflow",
+    semi: true,
+    singleQuote: true,
+    embeddedLanguageFormatting: "off", 
+    plugins: [
+      {
+        parsers: {
+          dataflow: {
+            astFormat: "estree",
+            locStart: (e) => e.start,
+            locEnd: (e) => e.end,
+            parse: (src) => {
+              const comments = [];
+              const tokens = [];
+              const program = ModuleParser.parse(src, {
+                onComment: comments,
+                onToken: tokens,
+                ranges: true,
+                allowAwaitOutsideFunction: true,
+                allowReturnOutsideFunction: true,
+                allowImportExportEverywhere: true
+              });
+              return {
+                ...program,
+                type: "Program",
+                body: program.cells
+              };
+            }
+          }
+        }
+      }
+    ]
+  })
+}
+
+// let body = [shouldAddParens ? "(" : "", path.call(print, "body"), shouldAddParens ? ")" : "", n.body.type === "Identifier" ? ";" : ""];
+function prettifyX(source) {
+  return prettier.format(source, {
+    semi: true,
+    singleQuote: true,
+    embeddedLanguageFormatting: "off", 
+    parser(text) {
+      const ast = ModuleParser.parse(text);
+      return {
+        ...ast,
+        body: ast.cells
+      };
+    },
+  });
+}
+function format(inFile, options) {
+  const {write=false} = options;
+  const src = readFileSync(inFile, "utf8");
+  const formatted = prettifyX(src);
+  if(write) {
+    writeFileSync(inFile, formatted, "utf8");
+  }
+  else {
+    console.log(formatted);
+  }
+}
+
+module.exports = {
+  format
+}
\ No newline at end of file
diff --git a/yarn.lock b/yarn.lock
index f64e8a1..41598e7 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -23,6 +23,11 @@
     acorn "^7.1.1"
     acorn-walk "^7.0.0"
 
+"@observablehq/prettier@^2.2.1-alpha.1":
+  version "2.2.1-alpha.1"
+  resolved "https://registry.yarnpkg.com/@observablehq/prettier/-/prettier-2.2.1-alpha.1.tgz#f84ba0372c0ccb5ec7e9bb1c3955f5de1fe92fca"
+  integrity sha512-1DZEC2xCtL1NRehFxfgj3nETzTCkioX2O8am5a7YrsA2AtvSZ6lvy4+YR/QS9Hbw6YJe6PnAETm6biSuVDyVgg==
+
 "@observablehq/runtime@4.9":
   version "4.9.0"
   resolved "https://registry.yarnpkg.com/@observablehq/runtime/-/runtime-4.9.0.tgz#eb359942df2b3fc76dadf74943cc6c60ad0cd259"