diff --git a/ui/frontend/Icon.tsx b/ui/frontend/Icon.tsx
index 6e44d7fa3..b4c656811 100644
--- a/ui/frontend/Icon.tsx
+++ b/ui/frontend/Icon.tsx
@@ -36,20 +36,26 @@ export const MoreOptionsActiveIcon = () => (
   </svg>
 );
 
-// M.D. 'settings',
-export const ConfigIcon = () => (
-  <svg className="icon" height="15" viewBox="0 0 24 24" width="15" opacity="0.5" xmlns="http://www.w3.org/2000/svg">
+const createConfigIcon = (size: string) => () => (
+  <svg className="icon" height={size} viewBox="0 0 24 24" width={size} opacity="0.5" xmlns="http://www.w3.org/2000/svg">
     <path d="M19.43 12.98c.04-.32.07-.64.07-.98s-.03-.66-.07-.98l2.11-1.65c.19-.15.24-.42.12-.64l-2-3.46c-.12-.22-.39-.3-.61-.22l-2.49 1c-.52-.4-1.08-.73-1.69-.98l-.38-2.65C14.46 2.18 14.25 2 14 2h-4c-.25 0-.46.18-.49.42l-.38 2.65c-.61.25-1.17.59-1.69.98l-2.49-1c-.23-.09-.49 0-.61.22l-2 3.46c-.13.22-.07.49.12.64l2.11 1.65c-.04.32-.07.65-.07.98s.03.66.07.98l-2.11 1.65c-.19.15-.24.42-.12.64l2 3.46c.12.22.39.3.61.22l2.49-1c.52.4 1.08.73 1.69.98l.38 2.65c.03.24.24.42.49.42h4c.25 0 .46-.18.49-.42l.38-2.65c.61-.25 1.17-.59 1.69-.98l2.49 1c.23.09.49 0 .61-.22l2-3.46c.12-.22.07-.49-.12-.64l-2.11-1.65zM12 15.5c-1.93 0-3.5-1.57-3.5-3.5s1.57-3.5 3.5-3.5 3.5 1.57 3.5 3.5-1.57 3.5-3.5 3.5z" />
   </svg>
-);
+)
 
-// M.D. 'help_outline'
-export const HelpIcon = () => (
-  <svg className="icon" height="18" viewBox="0 0 24 24" width="18" opacity="0.5" xmlns="http://www.w3.org/2000/svg">
+// M.D. 'settings',
+export const ConfigIcon = createConfigIcon('15');
+export const RustfmtTomlIcon = createConfigIcon('30');
+
+const createHelpIcon = (size: string) => () => (
+  <svg className="icon" height={size} viewBox="0 0 24 24" width={size} opacity="0.5" xmlns="http://www.w3.org/2000/svg">
     <path d="M11 18h2v-2h-2v2zm1-16C6.48 2 2 6.48 2 12s4.48 10 10 10 10-4.48 10-10S17.52 2 12 2zm0 18c-4.41 0-8-3.59-8-8s3.59-8 8-8 8 3.59 8 8-3.59 8-8 8zm0-14c-2.21 0-4 1.79-4 4h2c0-1.1.9-2 2-2s2 .9 2 2c0 2-3 1.75-3 5h2c0-2.25 3-2.5 3-5 0-2.21-1.79-4-4-4z" />
   </svg>
 );
 
+// M.D. 'help_outline'
+export const HelpIcon = createHelpIcon('18');
+export const RustfmtModalHelpIcon = createHelpIcon('24');
+
 export const CheckmarkIcon = () => (
   <svg className="icon icon--checkmark" height="18" viewBox="2 2 22 22" width="18" opacity="0.5" xmlns="http://www.w3.org/2000/svg">
     <path d="M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z" />
diff --git a/ui/frontend/Playground.tsx b/ui/frontend/Playground.tsx
index c99c1a244..d28eaa81b 100644
--- a/ui/frontend/Playground.tsx
+++ b/ui/frontend/Playground.tsx
@@ -5,11 +5,13 @@ import Editor from './Editor';
 import Header from './Header';
 import Notifications from './Notifications';
 import Output from './Output';
+import RustfmtTomlModal from './RustfmtTomlModal';
 import * as selectors from './selectors';
 import State from './state';
 
 const Playground: React.SFC = () => {
   const showNotifications = useSelector(selectors.anyNotificationsToShowSelector);
+  const showRustfmtTomlModal = useSelector((state: State) => state.rustfmt.show);
   const focus = useSelector((state: State) => state.output.meta.focus);
   const splitOrientation = useSelector((state: State) => state.configuration.orientation);
 
@@ -17,6 +19,10 @@ const Playground: React.SFC = () => {
   const splitClass = 'playground-split';
   const orientation = splitClass + '-' + splitOrientation;
 
+  const rustfmtModal = showRustfmtTomlModal
+    ? <RustfmtTomlModal />
+    : null
+
   return (
     <div>
       <div className="playground">
@@ -33,6 +39,7 @@ const Playground: React.SFC = () => {
         </div>
       </div>
       {showNotifications && <Notifications />}
+      {rustfmtModal}
     </div>
   );
 };
diff --git a/ui/frontend/RustfmtTomlModal.tsx b/ui/frontend/RustfmtTomlModal.tsx
new file mode 100644
index 000000000..ee2ad573c
--- /dev/null
+++ b/ui/frontend/RustfmtTomlModal.tsx
@@ -0,0 +1,62 @@
+import React, { useCallback } from 'react';
+import { useSelector, useDispatch } from 'react-redux';
+
+import { Rnd } from 'react-rnd';
+
+import * as actions from './actions';
+import { Close as CloseIcon, RustfmtModalHelpIcon } from './Icon';
+
+import TomlEditor from './TomlEditor';
+import State from './state';
+
+const ModalDefaultWidth = 320;
+const ModalDefaultHeight = 200;
+const DefaultState = {
+  x: (window.innerWidth / 2) - ModalDefaultWidth,
+  y: (window.innerHeight / 2) - ModalDefaultHeight,
+  width: ModalDefaultWidth,
+  height: ModalDefaultHeight,
+};
+
+const RustfmtTomlModal: React.SFC = () => {
+  const toml = useSelector((state: State) => state.rustfmt.toml);
+  const dispatch = useDispatch();
+
+  const onEditRustfmt = useCallback((c) => dispatch(actions.editRustfmtToml(c)), [dispatch]);
+  const formatDialog = useCallback(() => {
+    dispatch(actions.toggleRustfmtTomlModalShow());
+  }, [dispatch]);
+
+  const Close = <button className="button-menu-item" title="Close Dialog" onClick={formatDialog}>
+    <CloseIcon />
+  </button>
+
+  return (
+    <Rnd
+      className="rustfmt-modal"
+      default={DefaultState}
+      cancel=".toml-input-area"
+    >
+      <div className="backbone">
+        <div className="toml-header">
+          <div className="toml-header-label">rustfmt.toml</div>
+          <div className="icon-areas">
+            <HelpIcon />
+            {Close}
+          </div>
+        </div>
+        <TomlEditor
+          toml={toml}
+          onEditCode={onEditRustfmt} />
+      </div>
+    </Rnd>
+  );
+};
+
+const HelpIcon: React.SFC = () => (
+  <a title="View help" href="https://rust-lang.github.io/rustfmt">
+    <RustfmtModalHelpIcon />
+  </a>
+);
+
+export default RustfmtTomlModal;
diff --git a/ui/frontend/TomlEditor.tsx b/ui/frontend/TomlEditor.tsx
new file mode 100644
index 000000000..53b86607e
--- /dev/null
+++ b/ui/frontend/TomlEditor.tsx
@@ -0,0 +1,30 @@
+import React from 'react';
+
+type TomlEditorProps = {
+  toml: string;
+  onEditCode: (_: string) => any;
+}
+
+class TomlEditor extends React.PureComponent<TomlEditorProps> {
+  private _editor: HTMLTextAreaElement;
+
+  private onChange = e => this.props.onEditCode(e.target.value);
+  private trackEditor = component => this._editor = component;
+
+  public render() {
+    return (
+      <textarea
+        ref={this.trackEditor}
+        className="toml-input-area"
+        name="toml-input-area"
+        autoCapitalize="none"
+        autoComplete="off"
+        autoCorrect="off"
+        spellCheck={false}
+        value={this.props.toml}
+        onChange={this.onChange} />
+    );
+  }
+}
+
+export default TomlEditor;
\ No newline at end of file
diff --git a/ui/frontend/ToolsMenu.tsx b/ui/frontend/ToolsMenu.tsx
index f329951c6..25128c7cf 100644
--- a/ui/frontend/ToolsMenu.tsx
+++ b/ui/frontend/ToolsMenu.tsx
@@ -1,6 +1,7 @@
 import React, { useCallback } from 'react';
 import { useDispatch, useSelector } from 'react-redux';
 
+import { RustfmtTomlIcon } from './Icon';
 import ButtonMenuItem from './ButtonMenuItem';
 import MenuGroup from './MenuGroup';
 
@@ -32,15 +33,25 @@ const ToolsMenu: React.SFC<ToolsMenuProps> = props => {
     dispatch(actions.performFormat());
     props.close();
   }, [dispatch, props]);
+  const formatDialog = useCallback(() => {
+    dispatch(actions.toggleRustfmtTomlModalShow());
+  }, [dispatch]);
 
   return (
     <MenuGroup title="Tools">
-      <ButtonMenuItem
-        name="Rustfmt"
-        onClick={format}>
-        <div>Format this code with Rustfmt.</div>
-        <div className="tools-menu__aside">{rustfmtVersion} ({rustfmtVersionDetails})</div>
-      </ButtonMenuItem>
+      <div className="menu-item-wrapper">
+        <ButtonMenuItem
+          name="Rustfmt"
+          onClick={format}>
+          <div>Format this code with Rustfmt.</div>
+          <div className="tools-menu__aside">{rustfmtVersion} ({rustfmtVersionDetails})</div>
+        </ButtonMenuItem>
+
+        <div className="menu-right" onClick={formatDialog}>
+          <RustfmtTomlIcon />
+        </div>
+      </div>
+
       <ButtonMenuItem
         name="Clippy"
         onClick={clippy}>
diff --git a/ui/frontend/actions.ts b/ui/frontend/actions.ts
index 0b58b9b1c..9f77bc694 100644
--- a/ui/frontend/actions.ts
+++ b/ui/frontend/actions.ts
@@ -87,6 +87,8 @@ export enum ActionType {
   CompileWasmSucceeded = 'COMPILE_WASM_SUCCEEDED',
   CompileWasmFailed = 'COMPILE_WASM_FAILED',
   EditCode = 'EDIT_CODE',
+  EditRustfmtToml = 'EDIT_RUSTFMT_TOML',
+  ToggleRustfmtTomlModalShow = 'TOGGLE_RUSTFMT_TOML_MODAL_SHOW',
   AddMainFunction = 'ADD_MAIN_FUNCTION',
   EnableFeatureGate = 'ENABLE_FEATURE_GATE',
   GotoPosition = 'GOTO_POSITION',
@@ -415,6 +417,12 @@ export const performCompileToNightlyWasm =
 export const editCode = (code: string) =>
   createAction(ActionType.EditCode, { code });
 
+export const editRustfmtToml = (code: string) =>
+  createAction(ActionType.EditRustfmtToml, { code });
+
+export const toggleRustfmtTomlModalShow = () =>
+  createAction(ActionType.ToggleRustfmtTomlModalShow);
+
 export const addMainFunction = () =>
   createAction(ActionType.AddMainFunction);
 
@@ -429,6 +437,7 @@ const requestFormat = () =>
 
 interface FormatRequestBody {
   code: string;
+  rustfmtToml: string;
   edition: string;
 }
 
@@ -750,6 +759,8 @@ export type Action =
   | ReturnType<typeof receiveCompileWasmSuccess>
   | ReturnType<typeof receiveCompileWasmFailure>
   | ReturnType<typeof editCode>
+  | ReturnType<typeof editRustfmtToml>
+  | ReturnType<typeof toggleRustfmtTomlModalShow>
   | ReturnType<typeof addMainFunction>
   | ReturnType<typeof enableFeatureGate>
   | ReturnType<typeof gotoPosition>
diff --git a/ui/frontend/index.scss b/ui/frontend/index.scss
index c54ba016c..5d9711695 100644
--- a/ui/frontend/index.scss
+++ b/ui/frontend/index.scss
@@ -627,6 +627,7 @@ $header-transition: 0.2s ease-in-out;
 }
 
 .menu-item {
+  width: 100%;
   margin-bottom: 1em;
 
   &:last-child {
@@ -634,6 +635,25 @@ $header-transition: 0.2s ease-in-out;
   }
 }
 
+.menu-item-wrapper {
+  display: flex;
+  width: 100%;
+  margin-bottom: 1em;
+}
+
+.menu-right {
+  display: flex;
+  align-items: center;
+  border-left: solid $header-main-border 2px;
+
+  svg {
+    cursor: pointer;
+    &:hover {
+      color: $header-tint;
+    }
+  }
+}
+
 @mixin menu-item-title {
   font-size: 13px;
   font-weight: 600;
@@ -894,3 +914,35 @@ $header-transition: 0.2s ease-in-out;
       cursor: pointer;
     }
 }
+
+.rustfmt-modal {
+  border: 4px solid $border-color;
+  z-index: 10;
+
+  .backbone {
+    height: 100%;
+  }
+
+  .toml-header {
+    display: flex;
+    justify-content: space-between;
+    line-height: 30px;
+    background-color: $background;
+
+    .toml-header-label {
+      margin-left: 4px;
+    }
+
+    .icon-areas {
+      display: flex;
+      padding: 4px;
+    }
+  }
+
+  .toml-input-area {
+    width: 100%;
+    height: calc(100% - 30px);
+    resize: none;
+    border: none;
+  }
+}
diff --git a/ui/frontend/package.json b/ui/frontend/package.json
index 082cb5e72..bf48e8011 100644
--- a/ui/frontend/package.json
+++ b/ui/frontend/package.json
@@ -20,6 +20,7 @@
     "react-portal": "^4.1.4",
     "react-prism": "^4.0.0",
     "react-redux": "^7.0.0",
+    "react-rnd": "^10.1.4",
     "redux": "^4.0.0",
     "redux-thunk": "^2.1.0",
     "regenerator-runtime": "^0.13.2",
diff --git a/ui/frontend/reducers/index.ts b/ui/frontend/reducers/index.ts
index 4f89407e7..e7a31f77e 100644
--- a/ui/frontend/reducers/index.ts
+++ b/ui/frontend/reducers/index.ts
@@ -8,6 +8,7 @@ import notifications from './notifications';
 import output from './output';
 import page from './page';
 import position from './position';
+import rustfmt from './rustfmt';
 import versions from './versions';
 
 const playgroundApp = combineReducers({
@@ -19,6 +20,7 @@ const playgroundApp = combineReducers({
   output,
   page,
   position,
+  rustfmt,
   versions,
 });
 
diff --git a/ui/frontend/reducers/rustfmt.ts b/ui/frontend/reducers/rustfmt.ts
new file mode 100644
index 000000000..602dd656d
--- /dev/null
+++ b/ui/frontend/reducers/rustfmt.ts
@@ -0,0 +1,26 @@
+import { Action, ActionType } from '../actions';
+
+const DEFAULT: State = {
+  show: false,
+  toml: '',
+}
+
+export type State = {
+  show: boolean;
+  toml: string;
+};
+
+export default function code(state = DEFAULT, action: Action): State {
+  switch (action.type) {
+    case ActionType.EditRustfmtToml:
+      return {
+        ...state, toml: action.code,
+      };
+    case ActionType.ToggleRustfmtTomlModalShow:
+      return {
+        ...state, show: !state.show,
+      };
+    default:
+      return state;
+  }
+}
diff --git a/ui/frontend/selectors/index.ts b/ui/frontend/selectors/index.ts
index a66faa889..0c37c2084 100644
--- a/ui/frontend/selectors/index.ts
+++ b/ui/frontend/selectors/index.ts
@@ -6,6 +6,7 @@ import { State } from '../reducers';
 import { Backtrace, Channel, Edition, PrimaryActionAuto, PrimaryActionCore } from '../types';
 
 const codeSelector = (state: State) => state.code;
+const rustfmtSelector = (state: State) => state.rustfmt.toml;
 
 const HAS_TESTS_RE = /^\s*#\s*\[\s*test\s*([^"]*)]/m;
 export const hasTestsSelector = createSelector(codeSelector, code => !!code.match(HAS_TESTS_RE));
@@ -274,6 +275,7 @@ export const clippyRequestSelector = createSelector(
 
 export const formatRequestSelector = createSelector(
   codeSelector,
+  rustfmtSelector,
   editionSelector,
-  (code, edition) => ({ code, edition }),
+  (code, rustfmtToml, edition) => ({ code, edition, rustfmtToml }),
 );
diff --git a/ui/frontend/yarn.lock b/ui/frontend/yarn.lock
index ad1261ef4..8df129318 100644
--- a/ui/frontend/yarn.lock
+++ b/ui/frontend/yarn.lock
@@ -2023,6 +2023,11 @@ class-utils@^0.3.5:
     isobject "^3.0.0"
     static-extend "^0.1.1"
 
+classnames@^2.2.5:
+  version "2.2.6"
+  resolved "https://registry.yarnpkg.com/classnames/-/classnames-2.2.6.tgz#43935bffdd291f326dad0a205309b38d00f650ce"
+  integrity sha512-JR/iSQOSt+LQIWwrwEzJ9uk0xfN3mTVYMwt1Ir5mUcSN6pU+V4zQFFaJsclJbPuAUQH+yfWef6tm7l1quW3C8Q==
+
 clean-css@4.2.x:
   version "4.2.1"
   resolved "https://registry.yarnpkg.com/clean-css/-/clean-css-4.2.1.tgz#2d411ef76b8569b6d0c84068dabe85b0aa5e5c17"
@@ -3068,6 +3073,11 @@ fast-levenshtein@~2.0.6:
   resolved "https://registry.yarnpkg.com/fast-levenshtein/-/fast-levenshtein-2.0.6.tgz#3d8a5c66883a16a30ca8643e851f19baa7797917"
   integrity sha1-PYpcZog6FqMMqGQ+hR8Zuqd5eRc=
 
+fast-memoize@^2.5.1:
+  version "2.5.1"
+  resolved "https://registry.yarnpkg.com/fast-memoize/-/fast-memoize-2.5.1.tgz#c3519241e80552ce395e1a32dcdde8d1fd680f5d"
+  integrity sha512-xdmw296PCL01tMOXx9mdJSmWY29jQgxyuZdq0rEHMu+Tpe1eOEtCycoG6chzlcrWsNgpZP7oL8RiQr7+G6Bl6g==
+
 fb-watchman@^2.0.0:
   version "2.0.1"
   resolved "https://registry.yarnpkg.com/fb-watchman/-/fb-watchman-2.0.1.tgz#fc84fb39d2709cf3ff6d743706157bb5708a8a85"
@@ -5985,7 +5995,7 @@ prompts@^2.0.1:
     kleur "^3.0.3"
     sisteransi "^1.0.3"
 
-prop-types@^15.5.8, prop-types@^15.6.1, prop-types@^15.6.2, prop-types@^15.7.2:
+prop-types@^15.5.8, prop-types@^15.6.0, prop-types@^15.6.1, prop-types@^15.6.2, prop-types@^15.7.2:
   version "15.7.2"
   resolved "https://registry.yarnpkg.com/prop-types/-/prop-types-15.7.2.tgz#52c41e75b8c87e72b9d9360e0206b99dcbffa6c5"
   integrity sha512-8QQikdH7//R2vurIJSutZ1smHYTcLpRWEOlHnzcWHmBYrOGUysKwSsrC89BCiFj3CbrfJ/nXFdJepOVrY1GCHQ==
@@ -6114,6 +6124,13 @@ rc@^1.2.7:
     minimist "^1.2.0"
     strip-json-comments "~2.0.1"
 
+re-resizable@6.1.1:
+  version "6.1.1"
+  resolved "https://registry.yarnpkg.com/re-resizable/-/re-resizable-6.1.1.tgz#7ff7cfe92c0b9d8b0bceaa578aadaeeff8931eaf"
+  integrity sha512-ngzX5xbXi9LlIghJUYZaBDkJUIMLYqO3tQ2cJZoNprCRGhfHnbyufKm51MZRIOBlLigLzPPFKBxQE8ZLezKGfA==
+  dependencies:
+    fast-memoize "^2.5.1"
+
 react-copy-to-clipboard@^5.0.1:
   version "5.0.2"
   resolved "https://registry.yarnpkg.com/react-copy-to-clipboard/-/react-copy-to-clipboard-5.0.2.tgz#d82a437e081e68dfca3761fbd57dbf2abdda1316"
@@ -6132,6 +6149,14 @@ react-dom@^16.8.6:
     prop-types "^15.6.2"
     scheduler "^0.18.0"
 
+react-draggable@4.2.0:
+  version "4.2.0"
+  resolved "https://registry.yarnpkg.com/react-draggable/-/react-draggable-4.2.0.tgz#40cc5209082ca7d613104bf6daf31372cc0e1114"
+  integrity sha512-5wFq//gEoeTYprnd4ze8GrFc+Rbnx+9RkOMR3vk4EbWxj02U6L6T3yrlKeiw4X5CtjD2ma2+b3WujghcXNRzkw==
+  dependencies:
+    classnames "^2.2.5"
+    prop-types "^15.6.0"
+
 react-is@^16.7.0, react-is@^16.8.1, react-is@^16.8.4, react-is@^16.9.0:
   version "16.12.0"
   resolved "https://registry.yarnpkg.com/react-is/-/react-is-16.12.0.tgz#2cc0fe0fba742d97fd527c42a13bec4eeb06241c"
@@ -6174,6 +6199,15 @@ react-redux@^7.0.0:
     prop-types "^15.7.2"
     react-is "^16.9.0"
 
+react-rnd@^10.1.4:
+  version "10.1.4"
+  resolved "https://registry.yarnpkg.com/react-rnd/-/react-rnd-10.1.4.tgz#435e30e752e4251bb1a2d618ae58e543e542ae62"
+  integrity sha512-m2k5jYNcqhxUfUqnzp0Dj4hfqCnGgkMrCsCDAl+jspNrkz/u3Kpj/GyKFYhPdI3CCaY+25lwfTEP3rAMbb9IxA==
+  dependencies:
+    re-resizable "6.1.1"
+    react-draggable "4.2.0"
+    tslib "1.10.0"
+
 react@^16.8.6:
   version "16.12.0"
   resolved "https://registry.yarnpkg.com/react/-/react-16.12.0.tgz#0c0a9c6a142429e3614834d5a778e18aa78a0b83"
@@ -7405,7 +7439,7 @@ ts-loader@^6.0.0:
     micromatch "^4.0.0"
     semver "^6.0.0"
 
-tslib@^1.8.1, tslib@^1.9.0:
+tslib@1.10.0, tslib@^1.8.1, tslib@^1.9.0:
   version "1.10.0"
   resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.10.0.tgz#c3c19f95973fb0a62973fb09d90d961ee43e5c8a"
   integrity sha512-qOebF53frne81cf0S9B41ByenJ3/IuH8yJKngAX35CmiZySA0khhkovshKK+jGCaMnVomla7gVlIcc3EvKPbTQ==
diff --git a/ui/src/main.rs b/ui/src/main.rs
index 9a75acb03..e82c7b1aa 100644
--- a/ui/src/main.rs
+++ b/ui/src/main.rs
@@ -576,6 +576,8 @@ struct ExecuteResponse {
 #[derive(Debug, Clone, Deserialize)]
 struct FormatRequest {
     code: String,
+    #[serde(rename = "rustfmtToml")]
+    rustfmt_toml: String,
     #[serde(default)]
     edition: String,
 }
@@ -748,6 +750,7 @@ impl TryFrom<FormatRequest> for sandbox::FormatRequest {
     fn try_from(me: FormatRequest) -> Result<Self> {
         Ok(sandbox::FormatRequest {
             code: me.code,
+            rustfmt_toml: me.rustfmt_toml,
             edition: parse_edition(&me.edition)?,
         })
     }
diff --git a/ui/src/sandbox.rs b/ui/src/sandbox.rs
index f8efd2ee9..3d9f2b165 100644
--- a/ui/src/sandbox.rs
+++ b/ui/src/sandbox.rs
@@ -83,6 +83,7 @@ pub struct Sandbox {
     #[allow(dead_code)]
     scratch: TempDir,
     input_file: PathBuf,
+    rustfmt_toml: PathBuf,
     output_dir: PathBuf,
 }
 
@@ -104,6 +105,7 @@ impl Sandbox {
     pub fn new() -> Result<Self> {
         let scratch = TempDir::new("playground").context(UnableToCreateTempDir)?;
         let input_file = scratch.path().join("input.rs");
+        let rustfmt_toml = scratch.path().join("rustfmt.toml");
         let output_dir = scratch.path().join("output");
 
         fs::create_dir(&output_dir).context(UnableToCreateOutputDir)?;
@@ -112,6 +114,7 @@ impl Sandbox {
         Ok(Sandbox {
             scratch,
             input_file,
+            rustfmt_toml,
             output_dir,
         })
     }
@@ -184,6 +187,7 @@ impl Sandbox {
 
     pub fn format(&self, req: &FormatRequest) -> Result<FormatResponse> {
         self.write_source_code(&req.code)?;
+        self.write_rustfmt_toml(&req.rustfmt_toml)?;
         let command = self.format_command(req);
 
         let output = run_command_with_timeout(command)?;
@@ -301,6 +305,14 @@ impl Sandbox {
         Ok(())
     }
 
+    fn write_rustfmt_toml(&self, code: &str) -> Result<()> {
+      fs::write(&self.rustfmt_toml, code).context(UnableToCreateSourceFile)?;
+      fs::set_permissions(&self.rustfmt_toml, wide_open_permissions()).context(UnableToSetSourcePermissions)?;
+
+      log::debug!("Wrote {} bytes of source to rustfmt.toml", code.len());
+      Ok(())
+  }
+
     fn compile_command(&self, target: CompileTarget, channel: Channel, mode: Mode, tests: bool, req: impl CrateTypeRequest + EditionRequest + BacktraceRequest) -> Command {
         let mut cmd = self.docker_command(Some(req.crate_type()));
         set_execution_environment(&mut cmd, Some(target), &req);
@@ -373,6 +385,10 @@ impl Sandbox {
         mount_input_file.push("/playground/");
         mount_input_file.push(crate_type.file_name());
 
+        let mut mount_rustfmt = self.rustfmt_toml.as_os_str().to_os_string();
+        mount_rustfmt.push(":");
+        mount_rustfmt.push("/playground/rustfmt.toml");
+
         let mut mount_output_dir = self.output_dir.as_os_str().to_os_string();
         mount_output_dir.push(":");
         mount_output_dir.push("/playground-result");
@@ -381,6 +397,7 @@ impl Sandbox {
 
         cmd
             .arg("--volume").arg(&mount_input_file)
+            .arg("--volume").arg(&mount_rustfmt)
             .arg("--volume").arg(&mount_output_dir);
 
         cmd
@@ -746,6 +763,7 @@ pub struct ExecuteResponse {
 #[derive(Debug, Clone)]
 pub struct FormatRequest {
     pub code: String,
+    pub rustfmt_toml: String,
     pub edition: Option<Edition>,
 }
 
@@ -1119,6 +1137,7 @@ mod test {
     fn formatting_code() {
         let req = FormatRequest {
             code: "fn foo () { method_call(); }".to_string(),
+            rustfmt_toml: "".to_string(),
             edition: None,
         };
 
@@ -1134,13 +1153,25 @@ mod test {
 
     // Code that is only syntactically valid in Rust 2018
     const FORMAT_IN_EDITION_2018: &str = r#"fn main() { use std::num::ParseIntError; let result: Result<i32, ParseIntError> = try { "1".parse::<i32>()? + "2".parse::<i32>()? + "3".parse::<i32>()? }; assert_eq!(result, Ok(6)); }"#;
-
+    const FORMAT_USING_RUSTFMT_TOML: &str = r#"fn main() {
+    let lorem = vec![
+        "ipsum",
+        "dolor",
+        "sit",
+        "amet",
+        "consectetur",
+        "adipiscing",
+        "elit",
+    ];
+}
+  "#;
     const FORMAT_ERROR: &str = r#"error: expected identifier, found `"1"`"#;
 
     #[test]
     fn formatting_code_edition_2015() -> Result<()> {
         let req = FormatRequest {
             code: FORMAT_IN_EDITION_2018.to_string(),
+            rustfmt_toml: "".to_string(),
             edition: Some(Edition::Rust2015),
         };
 
@@ -1154,6 +1185,7 @@ mod test {
     fn formatting_code_edition_2018() -> Result<()> {
         let req = FormatRequest {
             code: FORMAT_IN_EDITION_2018.to_string(),
+            rustfmt_toml: "".to_string(),
             edition: Some(Edition::Rust2018),
         };
 
@@ -1170,6 +1202,30 @@ mod test {
         Ok(())
     }
 
+    #[test]
+    fn formatting_code_using_rustfmt_toml() -> Result<()> {
+        let req = FormatRequest {
+            code: FORMAT_USING_RUSTFMT_TOML.to_string(),
+            rustfmt_toml: r#"indent_style = "Visual""#.to_string(),
+            edition: Some(Edition::Rust2018),
+        };
+
+        let resp = Sandbox::new()?.format(&req)?;
+        assert!(!resp.stderr.contains(FORMAT_ERROR));
+
+        let lines: Vec<_> = resp.code.lines().collect();
+        assert_eq!(lines[0], r#"fn main() {"#);
+        assert_eq!(lines[1], r#"    let lorem = vec!["ipsum","#);
+        assert_eq!(lines[2], r#"                     "dolor","#);
+        assert_eq!(lines[3], r#"                     "sit","#);
+        assert_eq!(lines[4], r#"                     "amet","#);
+        assert_eq!(lines[5], r#"                     "consectetur","#);
+        assert_eq!(lines[6], r#"                     "adipiscing","#);
+        assert_eq!(lines[7], r#"                     "elit",];"#);
+        assert_eq!(lines[8], r#"}"#);
+        Ok(())
+    }
+
     #[test]
     fn linting_code() {
         let code = r#"