diff --git a/.babelrc.js b/.babelrc.js
index d35eff79a4..4af2b5dae4 100644
--- a/.babelrc.js
+++ b/.babelrc.js
@@ -9,14 +9,10 @@ module.exports = {
   ],
   env: {
     cjs: {
-      presets: [
-        ['@babel/preset-env', { modules: 'commonjs' }],
-      ],
+      presets: [['@babel/preset-env', { modules: 'commonjs' }]],
     },
     mjs: {
-      presets: [
-        ['@babel/preset-env', { modules: false }],
-      ],
+      presets: [['@babel/preset-env', { modules: false }]],
     },
   },
 };
diff --git a/.eslintrc.yml b/.eslintrc.yml
index d9a13b5dac..9f8b14af02 100644
--- a/.eslintrc.yml
+++ b/.eslintrc.yml
@@ -6,12 +6,8 @@ env:
   node: true
 plugins:
   - flowtype
-  - prettier
 
 rules:
-  # https://github.com/prettier/eslint-plugin-prettier#installation
-  prettier/prettier: error
-
   # `eslint-plugin-flowtype` rule list based on `v3.11.x`
   # https://github.com/gajus/eslint-plugin-flowtype#eslint-plugin-flowtype
 
@@ -35,7 +31,8 @@ rules:
   flowtype/require-readonly-react-props: off
   flowtype/require-return-type: off
   flowtype/require-types-at-top: off
-  flowtype/require-valid-file-annotation: [error, always, { annotationStyle: line, strict: true }]
+  flowtype/require-valid-file-annotation:
+    [error, always, { annotationStyle: line, strict: true }]
   flowtype/require-variable-type: off
   flowtype/sort-keys: off
   flowtype/spread-exact-type: off
@@ -130,7 +127,7 @@ rules:
   no-implied-eval: error
   no-invalid-this: off
   no-iterator: error
-  no-labels: [error, {allowLoop: true}]
+  no-labels: [error, { allowLoop: true }]
   no-lone-blocks: error
   no-loop-func: error
   no-magic-numbers: off
@@ -168,7 +165,7 @@ rules:
   require-await: off # TODO
   require-unicode-regexp: off
   vars-on-top: error
-  yoda: [error, never, {exceptRange: true}]
+  yoda: [error, never, { exceptRange: true }]
 
   # Strict Mode
   # https://eslint.org/docs/rules/#strict-mode
@@ -187,7 +184,8 @@ rules:
   no-undef: error
   no-undef-init: error
   no-undefined: off
-  no-unused-vars: [error, {vars: all, args: after-used, argsIgnorePattern: "^_"}]
+  no-unused-vars:
+    [error, { vars: all, args: after-used, argsIgnorePattern: '^_' }]
   no-use-before-define: off
 
   # Node.js and CommonJS
@@ -208,7 +206,7 @@ rules:
   # Stylistic Issues
   # https://eslint.org/docs/rules/#stylistic-issues
 
-  camelcase: [error, {properties: always}]
+  camelcase: [error, { properties: always }]
   capitalized-comments: off # maybe
   consistent-this: off
   func-name-matching: off
@@ -216,7 +214,7 @@ rules:
   func-style: off
   id-blacklist: off
   id-length: off
-  id-match: [error, "^(?:_?[a-zA-Z0-9]*)|[_A-Z0-9]+$"]
+  id-match: [error, '^(?:_?[a-zA-Z0-9]*)|[_A-Z0-9]+$']
   line-comment-position: off
   lines-around-comment: off
   lines-between-class-members: [error, always, { exceptAfterSingleLine: true }]
@@ -353,10 +351,10 @@ rules:
   yield-star-spacing: off
 
 overrides:
-  - files: "**/__tests__/**"
+  - files: '**/__tests__/**'
     rules:
       no-restricted-syntax: off
-  - files: "resources/**"
+  - files: 'resources/**'
     parserOptions:
       sourceType: script
     rules:
diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index fdbccf9802..0dd32f2d63 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -1,5 +1,4 @@
-Contributing to graphql-js
-==========================
+# Contributing to graphql-js
 
 We want to make contributing to this project as easy and transparent as
 possible. Hopefully this document makes the process for contributing clear and
@@ -72,23 +71,23 @@ This will watch the file system run any relevant lint, tests, and type checks au
 This project uses [Prettier](https://prettier.io/) for standard formatting. To
 ensure your pull request matches the style guides, run `npm run prettier`.
 
-* 2 spaces for indentation (no tabs)
-* 80 character line length strongly preferred.
-* Prefer `'` over `"`
-* ES6 syntax when possible. However do not rely on ES6-specific functions to be available.
-* Use [Flow types](https://flowtype.org/).
-* Use semicolons;
-* Trailing commas,
-* Avd abbr wrds.
+- 2 spaces for indentation (no tabs)
+- 80 character line length strongly preferred.
+- Prefer `'` over `"`
+- ES6 syntax when possible. However do not rely on ES6-specific functions to be available.
+- Use [Flow types](https://flowtype.org/).
+- Use semicolons;
+- Trailing commas,
+- Avd abbr wrds.
 
 ## Release on NPM
 
-*Only core contributors may release to NPM.*
+_Only core contributors may release to NPM._
 
 To release a new version on NPM, first ensure all tests pass with `npm test`,
 then use `npm version patch|minor|major` in order to increment the version in
 package.json and tag and commit a release. Then `git push && git push --tags`
-this change so Travis CI can deploy to NPM. *Do not run `npm publish` directly.*
+this change so Travis CI can deploy to NPM. _Do not run `npm publish` directly._
 Once published, add [release notes](https://github.com/graphql/graphql-js/tags).
 Use [semver](https://semver.org/) to determine which version part to increment.
 
diff --git a/.github/ISSUE_TEMPLATE.md b/.github/ISSUE_TEMPLATE.md
index a98cba9c25..d82363189e 100644
--- a/.github/ISSUE_TEMPLATE.md
+++ b/.github/ISSUE_TEMPLATE.md
@@ -10,7 +10,7 @@ Please do not post general questions directly as GitHub issues. They may sit for
 
 Before filing a new issue, make sure an issue for your problem doesn't already exist.
 
-The best way to get a bug fixed is to provide a *pull request* with a simplified failing test case (or better yet, include a fix).
+The best way to get a bug fixed is to provide a _pull request_ with a simplified failing test case (or better yet, include a fix).
 
 # Feature requests
 
diff --git a/.nycflowrc.yml b/.nycflowrc.yml
index ad201c4f31..4032fdd014 100644
--- a/.nycflowrc.yml
+++ b/.nycflowrc.yml
@@ -1,10 +1,10 @@
 include:
-  - "src/"
+  - 'src/'
 exclude:
-  - "src/polyfills"
+  - 'src/polyfills'
 clean: true
-temp-directory: "coverage/flow"
-report-dir: "coverage/flow"
+temp-directory: 'coverage/flow'
+report-dir: 'coverage/flow'
 skip-full: true
 skip-empty: true
 reporter: [json, html, text]
diff --git a/.nycrc.yml b/.nycrc.yml
index c15e75fa60..f6ead2c2e3 100644
--- a/.nycrc.yml
+++ b/.nycrc.yml
@@ -1,9 +1,9 @@
 include:
-  - "src/"
+  - 'src/'
 exclude:
-  - "src/polyfills"
+  - 'src/polyfills'
 clean: true
-temp-directory: "coverage/tests"
-report-dir: "coverage/tests"
+temp-directory: 'coverage/tests'
+report-dir: 'coverage/tests'
 skip-full: true
 reporter: [json, html, text]
diff --git a/.travis.yml b/.travis.yml
index 4c7d2a5a74..d0de783f5f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,10 +5,10 @@ cache: yarn
 
 # https://github.com/nodejs/Release
 node_js:
-- '12'
-- '10'
-- '8'
-- '6'
+  - '12'
+  - '10'
+  - '8'
+  - '6'
 
 script: |
   if [[ "$(node -pe process.version)" == v10.* ]]; then # Is latest LTS?
@@ -20,11 +20,11 @@ script: |
 
 jobs:
   include:
-  - stage: deploy
-    if: type = push AND branch = master
-    script: npm run gitpublish
-    skip_cleanup: true
-    node_js: '10'
+    - stage: deploy
+      if: type = push AND branch = master
+      script: npm run gitpublish
+      skip_cleanup: true
+      node_js: '10'
 
 notifications:
   irc:
@@ -33,7 +33,7 @@ notifications:
     on_failure: change
     skip_join: true
     channels:
-    - chat.freenode.net#graphql
+      - chat.freenode.net#graphql
   slack:
     secure: 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
 
diff --git a/README.md b/README.md
index e682214701..66f1a8af5c 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,6 @@ https://graphql.org/graphql-js/.
 
 Looking for help? Find resources [from the community](https://graphql.org/community/).
 
-
 ## Getting Started
 
 An overview of GraphQL in general is available in the
@@ -47,7 +46,7 @@ import {
   graphql,
   GraphQLSchema,
   GraphQLObjectType,
-  GraphQLString
+  GraphQLString,
 } from 'graphql';
 
 var schema = new GraphQLSchema({
@@ -58,10 +57,10 @@ var schema = new GraphQLSchema({
         type: GraphQLString,
         resolve() {
           return 'world';
-        }
-      }
-    }
-  })
+        },
+      },
+    },
+  }),
 });
 ```
 
@@ -76,13 +75,11 @@ Then, serve the result of a query against that type schema.
 var query = '{ hello }';
 
 graphql(schema, query).then(result => {
-
   // Prints
   // {
   //   data: { hello: "world" }
   // }
   console.log(result);
-
 });
 ```
 
@@ -94,7 +91,6 @@ it, reporting errors otherwise.
 var query = '{ boyhowdy }';
 
 graphql(schema, query).then(result => {
-
   // Prints
   // {
   //   errors: [
@@ -103,7 +99,6 @@ graphql(schema, query).then(result => {
   //   ]
   // }
   console.log(result);
-
 });
 ```
 
diff --git a/docs/APIReference-GraphQL.md b/docs/APIReference-GraphQL.md
index 3db7cdf841..3aea9e87ba 100644
--- a/docs/APIReference-GraphQL.md
+++ b/docs/APIReference-GraphQL.md
@@ -17,7 +17,7 @@ var { graphql } = require('graphql'); // CommonJS
 
 ## Overview
 
-*Entry Point*
+_Entry Point_
 
 <ul class="apiIndex">
   <li>
@@ -28,7 +28,7 @@ var { graphql } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Schema*
+_Schema_
 
 <ul class="apiIndex">
   <li>
@@ -39,7 +39,7 @@ var { graphql } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Type Definitions*
+_Type Definitions_
 
 <ul class="apiIndex">
   <li>
@@ -92,7 +92,7 @@ var { graphql } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Scalars*
+_Scalars_
 
 <ul class="apiIndex">
   <li>
@@ -127,7 +127,7 @@ var { graphql } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Errors*
+_Errors_
 
 <ul class="apiIndex">
   <li>
diff --git a/docs/APIReference-Language.md b/docs/APIReference-Language.md
index 340a1eab08..9c163cc316 100644
--- a/docs/APIReference-Language.md
+++ b/docs/APIReference-Language.md
@@ -16,7 +16,7 @@ var { Source } = require('graphql'); // CommonJS
 
 ## Overview
 
-*Source*
+_Source_
 
 <ul class="apiIndex">
   <li>
@@ -33,7 +33,7 @@ var { Source } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Lexer*
+_Lexer_
 
 <ul class="apiIndex">
   <li>
@@ -44,7 +44,7 @@ var { Source } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Parser*
+_Parser_
 
 <ul class="apiIndex">
   <li>
@@ -67,7 +67,7 @@ var { Source } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Visitor*
+_Visitor_
 
 <ul class="apiIndex">
   <li>
@@ -84,7 +84,7 @@ var { Source } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Printer*
+_Printer_
 
 <ul class="apiIndex">
   <li>
@@ -224,7 +224,7 @@ var editedAST = visit(ast, {
     //   visitor.BREAK: stop visiting altogether
     //   null: delete this node
     //   any value: replace this node with the returned value
-  }
+  },
 });
 ```
 
@@ -233,17 +233,17 @@ instead provide functions named the same as the kinds of AST nodes, or
 enter/leave visitors at a named key, leading to four permutations of
 visitor API:
 
-1) Named visitors triggered when entering a node a specific kind.
+1. Named visitors triggered when entering a node a specific kind.
 
 ```js
 visit(ast, {
   Kind(node) {
     // enter the "Kind" node
-  }
-})
+  },
+});
 ```
 
-2) Named visitors that trigger upon entering and leaving a node of
+2. Named visitors that trigger upon entering and leaving a node of
    a specific kind.
 
 ```js
@@ -259,7 +259,7 @@ visit(ast, {
 })
 ```
 
-3) Generic visitors that trigger upon entering and leaving any node.
+3. Generic visitors that trigger upon entering and leaving any node.
 
 ```js
 visit(ast, {
@@ -268,25 +268,25 @@ visit(ast, {
   },
   leave(node) {
     // leave any node
-  }
-})
+  },
+});
 ```
 
-4) Parallel visitors for entering and leaving nodes of a specific kind.
+4. Parallel visitors for entering and leaving nodes of a specific kind.
 
 ```js
 visit(ast, {
   enter: {
     Kind(node) {
       // enter the "Kind" node
-    }
+    },
   },
   leave: {
     Kind(node) {
       // leave the "Kind" node
-    }
-  }
-})
+    },
+  },
+});
 ```
 
 ### BREAK
diff --git a/docs/APIReference-TypeSystem.md b/docs/APIReference-TypeSystem.md
index 0a7ff72520..b777db1ad1 100644
--- a/docs/APIReference-TypeSystem.md
+++ b/docs/APIReference-TypeSystem.md
@@ -16,7 +16,7 @@ var { GraphQLSchema } = require('graphql'); // CommonJS
 
 ## Overview
 
-*Schema*
+_Schema_
 
 <ul class="apiIndex">
   <li>
@@ -27,7 +27,7 @@ var { GraphQLSchema } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Definitions*
+_Definitions_
 
 <ul class="apiIndex">
   <li>
@@ -80,7 +80,7 @@ var { GraphQLSchema } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Predicates*
+_Predicates_
 
 <ul class="apiIndex">
   <li>
@@ -114,7 +114,7 @@ var { GraphQLSchema } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Un-modifiers*
+_Un-modifiers_
 
 <ul class="apiIndex">
   <li>
@@ -131,7 +131,7 @@ var { GraphQLSchema } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Scalars*
+_Scalars_
 
 <ul class="apiIndex">
   <li>
@@ -228,7 +228,7 @@ var OddType = new GraphQLScalarType({
       return oddValue(parseInt(ast.value, 10));
     }
     return null;
-  }
+  },
 });
 
 function oddValue(value) {
@@ -305,7 +305,7 @@ When two types need to refer to each other, or a type needs to refer to
 itself in a field, you can use a function expression (aka a closure or a
 thunk) to supply the fields lazily.
 
-Note that resolver functions are provided the `source` object as the first parameter. 
+Note that resolver functions are provided the `source` object as the first parameter.
 However, if a resolver function is not provided, then the default resolver is
 used, which looks for a method on `source` of the same name as the field. If found,
 the method is called with `(args, context, info)`. Since it is a method on `source`,
@@ -322,10 +322,10 @@ var AddressType = new GraphQLObjectType({
     formatted: {
       type: GraphQLString,
       resolve(obj) {
-        return obj.number + ' ' + obj.street
-      }
-    }
-  }
+        return obj.number + ' ' + obj.street;
+      },
+    },
+  },
 });
 
 var PersonType = new GraphQLObjectType({
@@ -333,7 +333,7 @@ var PersonType = new GraphQLObjectType({
   fields: () => ({
     name: { type: GraphQLString },
     bestFriend: { type: PersonType },
-  })
+  }),
 });
 ```
 
@@ -363,8 +363,8 @@ when the field is resolved.
 var EntityType = new GraphQLInterfaceType({
   name: 'Entity',
   fields: {
-    name: { type: GraphQLString }
-  }
+    name: { type: GraphQLString },
+  },
 });
 ```
 
@@ -394,7 +394,7 @@ to determine which type is actually used when the field is resolved.
 ```js
 var PetType = new GraphQLUnionType({
   name: 'Pet',
-  types: [ DogType, CatType ],
+  types: [DogType, CatType],
   resolveType(value) {
     if (value instanceof Dog) {
       return DogType;
@@ -402,7 +402,7 @@ var PetType = new GraphQLUnionType({
     if (value instanceof Cat) {
       return CatType;
     }
-  }
+  },
 });
 ```
 
@@ -452,8 +452,8 @@ var RGBType = new GraphQLEnumType({
   values: {
     RED: { value: 0 },
     GREEN: { value: 1 },
-    BLUE: { value: 2 }
-  }
+    BLUE: { value: 2 },
+  },
 });
 ```
 
@@ -508,7 +508,7 @@ var GeoPoint = new GraphQLInputObjectType({
     lat: { type: new GraphQLNonNull(GraphQLFloat) },
     lon: { type: new GraphQLNonNull(GraphQLFloat) },
     alt: { type: GraphQLFloat, defaultValue: 0 },
-  }
+  },
 });
 ```
 
@@ -532,7 +532,7 @@ var PersonType = new GraphQLObjectType({
   fields: () => ({
     parents: { type: new GraphQLList(Person) },
     children: { type: new GraphQLList(Person) },
-  })
+  }),
 });
 ```
 
@@ -557,7 +557,7 @@ var RowType = new GraphQLObjectType({
   name: 'Row',
   fields: () => ({
     id: { type: new GraphQLNonNull(String) },
-  })
+  }),
 });
 ```
 
diff --git a/docs/APIReference-Utilities.md b/docs/APIReference-Utilities.md
index 2b0b0625ae..a90f386b58 100644
--- a/docs/APIReference-Utilities.md
+++ b/docs/APIReference-Utilities.md
@@ -17,7 +17,7 @@ var { introspectionQuery } = require('graphql'); // CommonJS
 
 ## Overview
 
-*Introspection*
+_Introspection_
 
 <ul class="apiIndex">
   <li>
@@ -34,7 +34,7 @@ var { introspectionQuery } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Schema Language*
+_Schema Language_
 
 <ul class="apiIndex">
   <li>
@@ -75,7 +75,7 @@ var { introspectionQuery } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Visitors*
+_Visitors_
 
 <ul class="apiIndex">
   <li>
@@ -86,7 +86,7 @@ var { introspectionQuery } = require('graphql'); // CommonJS
   </li>
 </ul>
 
-*Value Validation*
+_Value Validation_
 
 <ul class="apiIndex">
   <li>
@@ -108,7 +108,7 @@ var { introspectionQuery } = require('graphql'); // CommonJS
 ### introspectionQuery
 
 ```js
-var introspectionQuery: string
+var introspectionQuery: string;
 ```
 
 A GraphQL query that queries a server's introspection system for enough
@@ -192,6 +192,7 @@ function astFromValue(
   type?: ?GraphQLType
 ): ?Value
 ```
+
 Produces a GraphQL Input Value AST given a JavaScript value.
 
 Optionally, a GraphQL type may be provided, which will be used to
diff --git a/docs/Guides-ConstructingTypes.md b/docs/Guides-ConstructingTypes.md
index 9abd6e100d..b4a5fcb0c0 100644
--- a/docs/Guides-ConstructingTypes.md
+++ b/docs/Guides-ConstructingTypes.md
@@ -30,28 +30,31 @@ var schema = buildSchema(`
 
 // Maps id to User object
 var fakeDatabase = {
-  'a': {
+  a: {
     id: 'a',
     name: 'alice',
   },
-  'b': {
+  b: {
     id: 'b',
     name: 'bob',
   },
 };
 
 var root = {
-  user: function ({id}) {
+  user: function({ id }) {
     return fakeDatabase[id];
-  }
+  },
 };
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
@@ -65,11 +68,11 @@ var graphql = require('graphql');
 
 // Maps id to User object
 var fakeDatabase = {
-  'a': {
+  a: {
     id: 'a',
     name: 'alice',
   },
-  'b': {
+  b: {
     id: 'b',
     name: 'bob',
   },
@@ -81,7 +84,7 @@ var userType = new graphql.GraphQLObjectType({
   fields: {
     id: { type: graphql.GraphQLString },
     name: { type: graphql.GraphQLString },
-  }
+  },
 });
 
 // Define the Query type
@@ -92,22 +95,25 @@ var queryType = new graphql.GraphQLObjectType({
       type: userType,
       // `args` describes the arguments that the `user` query accepts
       args: {
-        id: { type: graphql.GraphQLString }
+        id: { type: graphql.GraphQLString },
       },
-      resolve: function (_, {id}) {
+      resolve: function(_, { id }) {
         return fakeDatabase[id];
-      }
-    }
-  }
+      },
+    },
+  },
 });
 
-var schema = new graphql.GraphQLSchema({query: queryType});
+var schema = new graphql.GraphQLSchema({ query: queryType });
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
diff --git a/docs/Tutorial-Authentication.md b/docs/Tutorial-Authentication.md
index 2ad93de475..3afe867c97 100644
--- a/docs/Tutorial-Authentication.md
+++ b/docs/Tutorial-Authentication.md
@@ -30,18 +30,21 @@ function loggingMiddleware(req, res, next) {
 }
 
 var root = {
-  ip: function (args, request) {
+  ip: function(args, request) {
     return request.ip;
-  }
+  },
 };
 
 var app = express();
 app.use(loggingMiddleware);
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
diff --git a/docs/Tutorial-BasicTypes.md b/docs/Tutorial-BasicTypes.md
index 4532f03f01..96febfaeac 100644
--- a/docs/Tutorial-BasicTypes.md
+++ b/docs/Tutorial-BasicTypes.md
@@ -44,11 +44,14 @@ var root = {
 };
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
diff --git a/docs/Tutorial-ExpressGraphQL.md b/docs/Tutorial-ExpressGraphQL.md
index 6fbfd57c67..b08ee9c70f 100644
--- a/docs/Tutorial-ExpressGraphQL.md
+++ b/docs/Tutorial-ExpressGraphQL.md
@@ -35,11 +35,14 @@ var root = {
 };
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
diff --git a/docs/Tutorial-GettingStarted.md b/docs/Tutorial-GettingStarted.md
index 0e492ae00d..bfa4592cce 100644
--- a/docs/Tutorial-GettingStarted.md
+++ b/docs/Tutorial-GettingStarted.md
@@ -40,7 +40,7 @@ var root = {
 };
 
 // Run the GraphQL query '{ hello }' and print out the response
-graphql(schema, '{ hello }', root).then((response) => {
+graphql(schema, '{ hello }', root).then(response => {
   console.log(response);
 });
 ```
@@ -54,7 +54,11 @@ node server.js
 You should see the GraphQL response printed out:
 
 ```javascript
-{ data: { hello: 'Hello world!' } }
+{
+  data: {
+    hello: 'Hello world!';
+  }
+}
 ```
 
 Congratulations - you just executed a GraphQL query!
diff --git a/docs/Tutorial-GraphQLClients.md b/docs/Tutorial-GraphQLClients.md
index 68485e4367..dee39b7c53 100644
--- a/docs/Tutorial-GraphQLClients.md
+++ b/docs/Tutorial-GraphQLClients.md
@@ -32,9 +32,9 @@ fetch('/graphql', {
   method: 'POST',
   headers: {
     'Content-Type': 'application/json',
-    'Accept': 'application/json',
+    Accept: 'application/json',
   },
-  body: JSON.stringify({query: "{ hello }"})
+  body: JSON.stringify({ query: '{ hello }' }),
 })
   .then(r => r.json())
   .then(data => console.log('data returned:', data));
@@ -69,12 +69,12 @@ fetch('/graphql', {
   method: 'POST',
   headers: {
     'Content-Type': 'application/json',
-    'Accept': 'application/json',
+    Accept: 'application/json',
   },
   body: JSON.stringify({
     query,
     variables: { dice, sides },
-  })
+  }),
 })
   .then(r => r.json())
   .then(data => console.log('data returned:', data));
diff --git a/docs/Tutorial-Mutations.md b/docs/Tutorial-Mutations.md
index 2ccde6ae68..3fdbd5c918 100644
--- a/docs/Tutorial-Mutations.md
+++ b/docs/Tutorial-Mutations.md
@@ -27,13 +27,13 @@ Both mutations and queries can be handled by root resolvers, so the root that im
 ```javascript
 var fakeDatabase = {};
 var root = {
-  setMessage: function ({message}) {
+  setMessage: function({ message }) {
     fakeDatabase.message = message;
     return message;
   },
-  getMessage: function () {
+  getMessage: function() {
     return fakeDatabase.message;
-  }
+  },
 };
 ```
 
@@ -101,7 +101,7 @@ var schema = buildSchema(`
 
 // If Message had any complex fields, we'd put them on this object.
 class Message {
-  constructor(id, {content, author}) {
+  constructor(id, { content, author }) {
     this.id = id;
     this.content = content;
     this.author = author;
@@ -112,20 +112,22 @@ class Message {
 var fakeDatabase = {};
 
 var root = {
-  getMessage: function ({id}) {
+  getMessage: function({ id }) {
     if (!fakeDatabase[id]) {
       throw new Error('no message exists with id ' + id);
     }
     return new Message(id, fakeDatabase[id]);
   },
-  createMessage: function ({input}) {
+  createMessage: function({ input }) {
     // Create a random id for our "database".
-    var id = require('crypto').randomBytes(10).toString('hex');
+    var id = require('crypto')
+      .randomBytes(10)
+      .toString('hex');
 
     fakeDatabase[id] = input;
     return new Message(id, input);
   },
-  updateMessage: function ({id, input}) {
+  updateMessage: function({ id, input }) {
     if (!fakeDatabase[id]) {
       throw new Error('no message exists with id ' + id);
     }
@@ -136,15 +138,17 @@ var root = {
 };
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000, () => {
   console.log('Running a GraphQL API server at localhost:4000/graphql');
 });
-
 ```
 
 To call a mutation, you must use the keyword `mutation` before your GraphQL query. To pass an input type, provide the data written as if it's a JSON object. For example, with the server defined above, you can create a new message and return the `id` of the new message with this operation:
@@ -175,7 +179,7 @@ fetch('/graphql', {
   method: 'POST',
   headers: {
     'Content-Type': 'application/json',
-    'Accept': 'application/json',
+    Accept: 'application/json',
   },
   body: JSON.stringify({
     query,
@@ -183,9 +187,9 @@ fetch('/graphql', {
       input: {
         author,
         content,
-      }
-    }
-  })
+      },
+    },
+  }),
 })
   .then(r => r.json())
   .then(data => console.log('data returned:', data));
diff --git a/docs/Tutorial-ObjectTypes.md b/docs/Tutorial-ObjectTypes.md
index 60a151f3ac..c5b569f292 100644
--- a/docs/Tutorial-ObjectTypes.md
+++ b/docs/Tutorial-ObjectTypes.md
@@ -40,7 +40,7 @@ class RandomDie {
     return 1 + Math.floor(Math.random() * this.numSides);
   }
 
-  roll({numRolls}) {
+  roll({ numRolls }) {
     var output = [];
     for (var i = 0; i < numRolls; i++) {
       output.push(this.rollOnce());
@@ -50,10 +50,10 @@ class RandomDie {
 }
 
 var root = {
-  getDie: function ({numSides}) {
+  getDie: function({ numSides }) {
     return new RandomDie(numSides || 6);
-  }
-}
+  },
+};
 ```
 
 For fields that don't use any arguments, you can use either properties on the object or instance methods. So for the example code above, both `numSides` and `rollOnce` can actually be used to implement GraphQL fields, so that code also implements the schema of:
@@ -100,7 +100,7 @@ class RandomDie {
     return 1 + Math.floor(Math.random() * this.numSides);
   }
 
-  roll({numRolls}) {
+  roll({ numRolls }) {
     var output = [];
     for (var i = 0; i < numRolls; i++) {
       output.push(this.rollOnce());
@@ -111,17 +111,20 @@ class RandomDie {
 
 // The root provides the top-level API endpoints
 var root = {
-  getDie: function ({numSides}) {
+  getDie: function({ numSides }) {
     return new RandomDie(numSides || 6);
-  }
-}
+  },
+};
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
diff --git a/docs/Tutorial-PassingArguments.md b/docs/Tutorial-PassingArguments.md
index 47154b488b..1660b43425 100644
--- a/docs/Tutorial-PassingArguments.md
+++ b/docs/Tutorial-PassingArguments.md
@@ -28,13 +28,13 @@ So far, our resolver functions took no arguments. When a resolver takes argument
 
 ```javascript
 var root = {
-  rollDice: function (args) {
+  rollDice: function(args) {
     var output = [];
     for (var i = 0; i < args.numDice; i++) {
       output.push(1 + Math.floor(Math.random() * (args.numSides || 6)));
     }
     return output;
-  }
+  },
 };
 ```
 
@@ -42,13 +42,13 @@ It's convenient to use [ES6 destructuring assignment](https://developer.mozilla.
 
 ```javascript
 var root = {
-  rollDice: function ({numDice, numSides}) {
+  rollDice: function({ numDice, numSides }) {
     var output = [];
     for (var i = 0; i < numDice; i++) {
       output.push(1 + Math.floor(Math.random() * (numSides || 6)));
     }
     return output;
-  }
+  },
 };
 ```
 
@@ -70,21 +70,24 @@ var schema = buildSchema(`
 
 // The root provides a resolver function for each API endpoint
 var root = {
-  rollDice: function ({numDice, numSides}) {
+  rollDice: function({ numDice, numSides }) {
     var output = [];
     for (var i = 0; i < numDice; i++) {
       output.push(1 + Math.floor(Math.random() * (numSides || 6)));
     }
     return output;
-  }
+  },
 };
 
 var app = express();
-app.use('/graphql', graphqlHTTP({
-  schema: schema,
-  rootValue: root,
-  graphiql: true,
-}));
+app.use(
+  '/graphql',
+  graphqlHTTP({
+    schema: schema,
+    rootValue: root,
+    graphiql: true,
+  }),
+);
 app.listen(4000);
 console.log('Running a GraphQL API server at localhost:4000/graphql');
 ```
@@ -114,12 +117,12 @@ fetch('/graphql', {
   method: 'POST',
   headers: {
     'Content-Type': 'application/json',
-    'Accept': 'application/json',
+    Accept: 'application/json',
   },
   body: JSON.stringify({
     query,
     variables: { dice, sides },
-  })
+  }),
 })
   .then(r => r.json())
   .then(data => console.log('data returned:', data));
diff --git a/package.json b/package.json
index c635dadfbb..358c118da4 100644
--- a/package.json
+++ b/package.json
@@ -23,13 +23,14 @@
     "node": ">= 6.x"
   },
   "scripts": {
-    "test": "npm run lint && npm run check && npm run testonly",
-    "test:ci": "yarn check --integrity && npm run lint -- --no-cache && npm run check && npm run testonly:cover && npm run build",
+    "test": "npm run prettier:check && npm run lint && npm run check && npm run testonly",
+    "test:ci": "yarn check --integrity && npm run prettier:check && npm run lint -- --no-cache && npm run check && npm run testonly:cover && npm run build",
     "testonly": "mocha --full-trace src/**/__tests__/**/*-test.js",
     "testonly:cover": "nyc npm run testonly",
     "lint": "eslint --cache --report-unused-disable-directives src resources",
     "benchmark": "node ./resources/benchmark.js",
-    "prettier": "prettier --write --list-different 'src/**/*.js' 'resources/**/*.js'",
+    "prettier": "prettier --ignore-path .gitignore --write --list-different '**/*.{js,md,json,yml}'",
+    "prettier:check": "prettier --ignore-path .gitignore --check '**/*.{js,md,json,yml}'",
     "check": "flow check",
     "check:cover": "node resources/check-cover.js && nyc report --nycrc-path .nycflowrc.yml",
     "build": "node resources/build.js",
@@ -52,7 +53,6 @@
     "chai": "4.2.0",
     "eslint": "5.16.0",
     "eslint-plugin-flowtype": "3.11.1",
-    "eslint-plugin-prettier": "3.1.0",
     "flow-bin": "0.102.0",
     "mocha": "6.1.4",
     "nyc": "14.1.1",
diff --git a/src/README.md b/src/README.md
index ae57712060..4fa588f20a 100644
--- a/src/README.md
+++ b/src/README.md
@@ -1,5 +1,4 @@
-GraphQL JS
-----------
+## GraphQL JS
 
 The primary `graphql` module includes everything you need to define a GraphQL
 schema and fulfill GraphQL requests.
@@ -11,14 +10,14 @@ var GraphQL = require('graphql'); // CommonJS
 
 Each sub directory within is a sub-module of graphql-js:
 
-* [`graphql/language`](language/README.md): Parse and operate on the GraphQL
+- [`graphql/language`](language/README.md): Parse and operate on the GraphQL
   language.
-* [`graphql/type`](type/README.md): Define GraphQL types and schema.
-* [`graphql/validation`](validation/README.md): The Validation phase of
+- [`graphql/type`](type/README.md): Define GraphQL types and schema.
+- [`graphql/validation`](validation/README.md): The Validation phase of
   fulfilling a GraphQL result.
-* [`graphql/execution`](execution/README.md): The Execution phase of fulfilling
+- [`graphql/execution`](execution/README.md): The Execution phase of fulfilling
   a GraphQL request.
-* [`graphql/error`](error/README.md): Creating and formating GraphQL errors.
-* [`graphql/utilities`](utilities/README.md): Common useful computations upon
+- [`graphql/error`](error/README.md): Creating and formating GraphQL errors.
+- [`graphql/utilities`](utilities/README.md): Common useful computations upon
   the GraphQL language and type objects.
-* [`graphql/subscription`](subscription/README.md): Subscribe to data updates.
+- [`graphql/subscription`](subscription/README.md): Subscribe to data updates.
diff --git a/src/__fixtures__/github-schema.json b/src/__fixtures__/github-schema.json
index 2ac97ffd9c..7352a87fa3 100644
--- a/src/__fixtures__/github-schema.json
+++ b/src/__fixtures__/github-schema.json
@@ -56774,11 +56774,7 @@
         {
           "name": "include",
           "description": "Directs the executor to include this field or fragment only when the `if` argument is true.",
-          "locations": [
-            "FIELD",
-            "FRAGMENT_SPREAD",
-            "INLINE_FRAGMENT"
-          ],
+          "locations": ["FIELD", "FRAGMENT_SPREAD", "INLINE_FRAGMENT"],
           "args": [
             {
               "name": "if",
@@ -56799,11 +56795,7 @@
         {
           "name": "skip",
           "description": "Directs the executor to skip this field or fragment when the `if` argument is true.",
-          "locations": [
-            "FIELD",
-            "FRAGMENT_SPREAD",
-            "INLINE_FRAGMENT"
-          ],
+          "locations": ["FIELD", "FRAGMENT_SPREAD", "INLINE_FRAGMENT"],
           "args": [
             {
               "name": "if",
@@ -56824,10 +56816,7 @@
         {
           "name": "deprecated",
           "description": "Marks an element of a GraphQL schema as no longer supported.",
-          "locations": [
-            "FIELD_DEFINITION",
-            "ENUM_VALUE"
-          ],
+          "locations": ["FIELD_DEFINITION", "ENUM_VALUE"],
           "args": [
             {
               "name": "reason",
diff --git a/src/error/README.md b/src/error/README.md
index 8ecc8303ad..750c351033 100644
--- a/src/error/README.md
+++ b/src/error/README.md
@@ -1,5 +1,4 @@
-GraphQL Errors
---------------
+## GraphQL Errors
 
 The `graphql/error` module is responsible for creating and formatting
 GraphQL errors.
diff --git a/src/execution/README.md b/src/execution/README.md
index 7b875646ee..6540f323fe 100644
--- a/src/execution/README.md
+++ b/src/execution/README.md
@@ -1,5 +1,4 @@
-GraphQL Execution
------------------
+## GraphQL Execution
 
 The `graphql/execution` module is responsible for the execution phase of
 fulfilling a GraphQL request.
diff --git a/src/jsutils/README.md b/src/jsutils/README.md
index 8c1e5f97d3..9eb96485e1 100644
--- a/src/jsutils/README.md
+++ b/src/jsutils/README.md
@@ -1,5 +1,4 @@
-JavaScript Utils
-----------------
+## JavaScript Utils
 
 This directory contains dependency-free JavaScript utility functions used
 throughout the codebase.
diff --git a/src/language/README.md b/src/language/README.md
index d5043f482c..68cc9fd4a7 100644
--- a/src/language/README.md
+++ b/src/language/README.md
@@ -1,5 +1,4 @@
-GraphQL Language
-----------------
+## GraphQL Language
 
 The `graphql/language` module is responsible for parsing and operating on the
 GraphQL language.
diff --git a/src/polyfills/README.md b/src/polyfills/README.md
index 55054b2312..20c9f6ee58 100644
--- a/src/polyfills/README.md
+++ b/src/polyfills/README.md
@@ -1,5 +1,4 @@
-Polyfills
----------
+## Polyfills
 
 This directory contains dependency-free polyfills for ES6 & ES7 functions used
 throughout the codebase.
diff --git a/src/subscription/README.md b/src/subscription/README.md
index dd47efaf54..c938354c2b 100644
--- a/src/subscription/README.md
+++ b/src/subscription/README.md
@@ -1,5 +1,4 @@
-GraphQL Subscription
------------------
+## GraphQL Subscription
 
 The `graphql/subscription` module is responsible for subscribing to updates on specific data.
 
diff --git a/src/type/README.md b/src/type/README.md
index 9fd9e8a802..1c03491a3a 100644
--- a/src/type/README.md
+++ b/src/type/README.md
@@ -1,5 +1,4 @@
-GraphQL Type System
--------------------
+## GraphQL Type System
 
 The `graphql/type` module is responsible for defining GraphQL types and schema.
 
diff --git a/src/utilities/README.md b/src/utilities/README.md
index a48dfce7da..0e626e2325 100644
--- a/src/utilities/README.md
+++ b/src/utilities/README.md
@@ -1,5 +1,4 @@
-GraphQL Utilities
------------------
+## GraphQL Utilities
 
 The `graphql/utilities` module contains common useful computations to use with
 the GraphQL language and type objects.
diff --git a/src/validation/README.md b/src/validation/README.md
index ad4a486c58..8a4a1c85f0 100644
--- a/src/validation/README.md
+++ b/src/validation/README.md
@@ -1,5 +1,4 @@
-GraphQL Validation
-------------------
+## GraphQL Validation
 
 The `graphql/validation` module fulfills the Validation phase of fulfilling a
 GraphQL result.
diff --git a/yarn.lock b/yarn.lock
index c12e1d923b..d42cb20d2e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1103,13 +1103,6 @@ eslint-plugin-flowtype@3.11.1:
   dependencies:
     lodash "^4.17.11"
 
-eslint-plugin-prettier@3.1.0:
-  version "3.1.0"
-  resolved "https://registry.yarnpkg.com/eslint-plugin-prettier/-/eslint-plugin-prettier-3.1.0.tgz#8695188f95daa93b0dc54b249347ca3b79c4686d"
-  integrity sha512-XWX2yVuwVNLOUhQijAkXz+rMPPoCr7WFiAl8ig6I7Xn+pPVhDhzg4DxHpmbeb0iqjO9UronEA3Tb09ChnFVHHA==
-  dependencies:
-    prettier-linter-helpers "^1.0.0"
-
 eslint-scope@3.7.1:
   version "3.7.1"
   resolved "https://registry.yarnpkg.com/eslint-scope/-/eslint-scope-3.7.1.tgz#3d63c3edfda02e06e01a452ad88caacc7cdcb6e8"
@@ -1243,11 +1236,6 @@ fast-deep-equal@^2.0.1:
   resolved "https://registry.yarnpkg.com/fast-deep-equal/-/fast-deep-equal-2.0.1.tgz#7b05218ddf9667bf7f370bf7fdb2cb15fdd0aa49"
   integrity sha1-ewUhjd+WZ79/Nwv3/bLLFf3Qqkk=
 
-fast-diff@^1.1.2:
-  version "1.2.0"
-  resolved "https://registry.yarnpkg.com/fast-diff/-/fast-diff-1.2.0.tgz#73ee11982d86caaf7959828d519cfe927fac5f03"
-  integrity sha512-xJuoT5+L99XlZ8twedaRf6Ax2TgQVxvgZOYoPKqZufmJib0tL2tegPBOZb1pVNgIhlqDlA0eO0c3wBvQcmzx4w==
-
 fast-json-stable-stringify@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/fast-json-stable-stringify/-/fast-json-stable-stringify-2.0.0.tgz#d5142c0caee6b1189f87d3a76111064f86c8bbf2"
@@ -2153,13 +2141,6 @@ prelude-ls@~1.1.2:
   resolved "https://registry.yarnpkg.com/prelude-ls/-/prelude-ls-1.1.2.tgz#21932a549f5e52ffd9a827f570e04be62a97da54"
   integrity sha1-IZMqVJ9eUv/ZqCf1cOBL5iqX2lQ=
 
-prettier-linter-helpers@^1.0.0:
-  version "1.0.0"
-  resolved "https://registry.yarnpkg.com/prettier-linter-helpers/-/prettier-linter-helpers-1.0.0.tgz#d23d41fe1375646de2d0104d3454a3008802cf7b"
-  integrity sha512-GbK2cP9nraSSUF9N2XwUwqfzlAFlMNYYl+ShE/V+H8a9uNl/oUqB1w2EL54Jh0OlyRSd8RfWYJ3coVS4TROP2w==
-  dependencies:
-    fast-diff "^1.1.2"
-
 prettier@1.18.2:
   version "1.18.2"
   resolved "https://registry.yarnpkg.com/prettier/-/prettier-1.18.2.tgz#6823e7c5900017b4bd3acf46fe9ac4b4d7bda9ea"