diff --git a/src/language/parser.d.ts b/src/language/parser.d.ts
index 60cbf20e3b..443139c792 100644
--- a/src/language/parser.d.ts
+++ b/src/language/parser.d.ts
@@ -1,6 +1,56 @@
-import { Source } from './source';
-import { TypeNode, ValueNode, DocumentNode } from './ast';
+import { Maybe } from '../jsutils/Maybe';
+import { GraphQLError } from '../error/GraphQLError';
 
+import {
+  Token,
+  Location,
+  NameNode,
+  VariableNode,
+  DocumentNode,
+  DefinitionNode,
+  OperationDefinitionNode,
+  OperationTypeNode,
+  VariableDefinitionNode,
+  SelectionSetNode,
+  SelectionNode,
+  FieldNode,
+  ArgumentNode,
+  FragmentSpreadNode,
+  InlineFragmentNode,
+  FragmentDefinitionNode,
+  ValueNode,
+  StringValueNode,
+  ListValueNode,
+  ObjectValueNode,
+  ObjectFieldNode,
+  DirectiveNode,
+  TypeNode,
+  NamedTypeNode,
+  TypeSystemDefinitionNode,
+  SchemaDefinitionNode,
+  OperationTypeDefinitionNode,
+  ScalarTypeDefinitionNode,
+  ObjectTypeDefinitionNode,
+  FieldDefinitionNode,
+  InputValueDefinitionNode,
+  InterfaceTypeDefinitionNode,
+  UnionTypeDefinitionNode,
+  EnumTypeDefinitionNode,
+  EnumValueDefinitionNode,
+  InputObjectTypeDefinitionNode,
+  DirectiveDefinitionNode,
+  TypeSystemExtensionNode,
+  SchemaExtensionNode,
+  ScalarTypeExtensionNode,
+  ObjectTypeExtensionNode,
+  InterfaceTypeExtensionNode,
+  UnionTypeExtensionNode,
+  EnumTypeExtensionNode,
+  InputObjectTypeExtensionNode,
+} from './ast';
+import { TokenKindEnum } from './tokenKind';
+import { Source } from './source';
+import { Lexer } from './lexer';
 /**
  * Configuration options to control parser behavior
  */
@@ -64,3 +114,469 @@ export function parseType(
   source: string | Source,
   options?: ParseOptions,
 ): TypeNode;
+
+/**
+ * This class is exported only to assist people in implementing their own parsers
+ * without duplicating too much code and should be used only as last resort for cases
+ * such as experimental syntax or if certain features could not be contributed upstream.
+ *
+ * It is still part of the internal API and is versioned, so any changes to it are never
+ * considered breaking changes. If you still need to support multiple versions of the
+ * library, please use the `versionInfo` variable for version detection.
+ *
+ * @internal
+ */
+export declare class Parser {
+  _options: Maybe<ParseOptions>;
+  _lexer: Lexer;
+
+  constructor(source: string | Source, options?: ParseOptions);
+
+  /**
+   * Converts a name lex token into a name parse node.
+   */
+  parseName(): NameNode;
+
+  /**
+   * Document : Definition+
+   */
+  parseDocument(): DocumentNode;
+
+  /**
+   * Definition :
+   *   - ExecutableDefinition
+   *   - TypeSystemDefinition
+   *   - TypeSystemExtension
+   *
+   * ExecutableDefinition :
+   *   - OperationDefinition
+   *   - FragmentDefinition
+   */
+  parseDefinition(): DefinitionNode;
+
+  /**
+   * OperationDefinition :
+   *  - SelectionSet
+   *  - OperationType Name? VariableDefinitions? Directives? SelectionSet
+   */
+  parseOperationDefinition(): OperationDefinitionNode;
+
+  /**
+   * OperationType : one of query mutation subscription
+   */
+  parseOperationType(): OperationTypeNode;
+
+  /**
+   * VariableDefinitions : ( VariableDefinition+ )
+   */
+  parseVariableDefinitions(): Array<VariableDefinitionNode>;
+
+  /**
+   * VariableDefinition : Variable : Type DefaultValue? Directives[Const]?
+   */
+  parseVariableDefinition(): VariableDefinitionNode;
+
+  /**
+   * Variable : $ Name
+   */
+  parseVariable(): VariableNode;
+
+  /**
+   * SelectionSet : { Selection+ }
+   */
+  parseSelectionSet(): SelectionSetNode;
+
+  /**
+   * Selection :
+   *   - Field
+   *   - FragmentSpread
+   *   - InlineFragment
+   */
+  parseSelection(): SelectionNode;
+
+  /**
+   * Field : Alias? Name Arguments? Directives? SelectionSet?
+   *
+   * Alias : Name :
+   */
+  parseField(): FieldNode;
+
+  /**
+   * Arguments[Const] : ( Argument[?Const]+ )
+   */
+  parseArguments(isConst: boolean): Array<ArgumentNode>;
+
+  /**
+   * Argument[Const] : Name : Value[?Const]
+   */
+  parseArgument(): ArgumentNode;
+
+  parseConstArgument(): ArgumentNode;
+
+  /**
+   * Corresponds to both FragmentSpread and InlineFragment in the spec.
+   *
+   * FragmentSpread : ... FragmentName Directives?
+   *
+   * InlineFragment : ... TypeCondition? Directives? SelectionSet
+   */
+  parseFragment(): FragmentSpreadNode | InlineFragmentNode;
+
+  /**
+   * FragmentDefinition :
+   *   - fragment FragmentName on TypeCondition Directives? SelectionSet
+   *
+   * TypeCondition : NamedType
+   */
+  parseFragmentDefinition(): FragmentDefinitionNode;
+
+  /**
+   * FragmentName : Name but not `on`
+   */
+  parseFragmentName(): NameNode;
+
+  /**
+   * Value[Const] :
+   *   - [~Const] Variable
+   *   - IntValue
+   *   - FloatValue
+   *   - StringValue
+   *   - BooleanValue
+   *   - NullValue
+   *   - EnumValue
+   *   - ListValue[?Const]
+   *   - ObjectValue[?Const]
+   *
+   * BooleanValue : one of `true` `false`
+   *
+   * NullValue : `null`
+   *
+   * EnumValue : Name but not `true`, `false` or `null`
+   */
+  parseValueLiteral(isConst: boolean): ValueNode;
+
+  parseStringLiteral(): StringValueNode;
+
+  /**
+   * ListValue[Const] :
+   *   - [ ]
+   *   - [ Value[?Const]+ ]
+   */
+  parseList(isConst: boolean): ListValueNode;
+
+  /**
+   * ObjectValue[Const] :
+   *   - { }
+   *   - { ObjectField[?Const]+ }
+   */
+  parseObject(isConst: boolean): ObjectValueNode;
+
+  /**
+   * ObjectField[Const] : Name : Value[?Const]
+   */
+  parseObjectField(isConst: boolean): ObjectFieldNode;
+
+  /**
+   * Directives[Const] : Directive[?Const]+
+   */
+  parseDirectives(isConst: boolean): Array<DirectiveNode>;
+
+  /**
+   * Directive[Const] : @ Name Arguments[?Const]?
+   */
+  parseDirective(isConst: boolean): DirectiveNode;
+
+  /**
+   * Type :
+   *   - NamedType
+   *   - ListType
+   *   - NonNullType
+   */
+  parseTypeReference(): TypeNode;
+
+  /**
+   * NamedType : Name
+   */
+  parseNamedType(): NamedTypeNode;
+
+  /**
+   * TypeSystemDefinition :
+   *   - SchemaDefinition
+   *   - TypeDefinition
+   *   - DirectiveDefinition
+   *
+   * TypeDefinition :
+   *   - ScalarTypeDefinition
+   *   - ObjectTypeDefinition
+   *   - InterfaceTypeDefinition
+   *   - UnionTypeDefinition
+   *   - EnumTypeDefinition
+   *   - InputObjectTypeDefinition
+   */
+  parseTypeSystemDefinition(): TypeSystemDefinitionNode;
+
+  peekDescription(): boolean;
+
+  /**
+   * Description : StringValue
+   */
+  parseDescription(): undefined | StringValueNode;
+
+  /**
+   * SchemaDefinition : Description? schema Directives[Const]? { OperationTypeDefinition+ }
+   */
+  parseSchemaDefinition(): SchemaDefinitionNode;
+
+  /**
+   * OperationTypeDefinition : OperationType : NamedType
+   */
+  parseOperationTypeDefinition(): OperationTypeDefinitionNode;
+
+  /**
+   * ScalarTypeDefinition : Description? scalar Name Directives[Const]?
+   */
+  parseScalarTypeDefinition(): ScalarTypeDefinitionNode;
+
+  /**
+   * ObjectTypeDefinition :
+   *   Description?
+   *   type Name ImplementsInterfaces? Directives[Const]? FieldsDefinition?
+   */
+  parseObjectTypeDefinition(): ObjectTypeDefinitionNode;
+
+  /**
+   * ImplementsInterfaces :
+   *   - implements `&`? NamedType
+   *   - ImplementsInterfaces & NamedType
+   */
+  parseImplementsInterfaces(): Array<NamedTypeNode>;
+
+  /**
+   * FieldsDefinition : { FieldDefinition+ }
+   */
+  parseFieldsDefinition(): Array<FieldDefinitionNode>;
+
+  /**
+   * FieldDefinition :
+   *   - Description? Name ArgumentsDefinition? : Type Directives[Const]?
+   */
+  parseFieldDefinition(): FieldDefinitionNode;
+
+  /**
+   * ArgumentsDefinition : ( InputValueDefinition+ )
+   */
+  parseArgumentDefs(): Array<InputValueDefinitionNode>;
+
+  /**
+   * InputValueDefinition :
+   *   - Description? Name : Type DefaultValue? Directives[Const]?
+   */
+  parseInputValueDef(): InputValueDefinitionNode;
+
+  /**
+   * InterfaceTypeDefinition :
+   *   - Description? interface Name Directives[Const]? FieldsDefinition?
+   */
+  parseInterfaceTypeDefinition(): InterfaceTypeDefinitionNode;
+
+  /**
+   * UnionTypeDefinition :
+   *   - Description? union Name Directives[Const]? UnionMemberTypes?
+   */
+  parseUnionTypeDefinition(): UnionTypeDefinitionNode;
+
+  /**
+   * UnionMemberTypes :
+   *   - = `|`? NamedType
+   *   - UnionMemberTypes | NamedType
+   */
+  parseUnionMemberTypes(): Array<NamedTypeNode>;
+
+  /**
+   * EnumTypeDefinition :
+   *   - Description? enum Name Directives[Const]? EnumValuesDefinition?
+   */
+  parseEnumTypeDefinition(): EnumTypeDefinitionNode;
+
+  /**
+   * EnumValuesDefinition : { EnumValueDefinition+ }
+   */
+  parseEnumValuesDefinition(): Array<EnumValueDefinitionNode>;
+
+  /**
+   * EnumValueDefinition : Description? EnumValue Directives[Const]?
+   *
+   * EnumValue : Name
+   */
+  parseEnumValueDefinition(): EnumValueDefinitionNode;
+
+  /**
+   * InputObjectTypeDefinition :
+   *   - Description? input Name Directives[Const]? InputFieldsDefinition?
+   */
+  parseInputObjectTypeDefinition(): InputObjectTypeDefinitionNode;
+
+  /**
+   * InputFieldsDefinition : { InputValueDefinition+ }
+   */
+  parseInputFieldsDefinition(): Array<InputValueDefinitionNode>;
+
+  /**
+   * TypeSystemExtension :
+   *   - SchemaExtension
+   *   - TypeExtension
+   *
+   * TypeExtension :
+   *   - ScalarTypeExtension
+   *   - ObjectTypeExtension
+   *   - InterfaceTypeExtension
+   *   - UnionTypeExtension
+   *   - EnumTypeExtension
+   *   - InputObjectTypeDefinition
+   */
+  parseTypeSystemExtension(): TypeSystemExtensionNode;
+
+  /**
+   * SchemaExtension :
+   *  - extend schema Directives[Const]? { OperationTypeDefinition+ }
+   *  - extend schema Directives[Const]
+   */
+  parseSchemaExtension(): SchemaExtensionNode;
+
+  /**
+   * ScalarTypeExtension :
+   *   - extend scalar Name Directives[Const]
+   */
+  parseScalarTypeExtension(): ScalarTypeExtensionNode;
+
+  /**
+   * ObjectTypeExtension :
+   *  - extend type Name ImplementsInterfaces? Directives[Const]? FieldsDefinition
+   *  - extend type Name ImplementsInterfaces? Directives[Const]
+   *  - extend type Name ImplementsInterfaces
+   */
+  parseObjectTypeExtension(): ObjectTypeExtensionNode;
+
+  /**
+   * InterfaceTypeExtension :
+   *  - extend interface Name ImplementsInterfaces? Directives[Const]? FieldsDefinition
+   *  - extend interface Name ImplementsInterfaces? Directives[Const]
+   *  - extend interface Name ImplementsInterfaces
+   */
+  parseInterfaceTypeExtension(): InterfaceTypeExtensionNode;
+
+  /**
+   * UnionTypeExtension :
+   *   - extend union Name Directives[Const]? UnionMemberTypes
+   *   - extend union Name Directives[Const]
+   */
+  parseUnionTypeExtension(): UnionTypeExtensionNode;
+
+  /**
+   * EnumTypeExtension :
+   *   - extend enum Name Directives[Const]? EnumValuesDefinition
+   *   - extend enum Name Directives[Const]
+   */
+  parseEnumTypeExtension(): EnumTypeExtensionNode;
+
+  /**
+   * InputObjectTypeExtension :
+   *   - extend input Name Directives[Const]? InputFieldsDefinition
+   *   - extend input Name Directives[Const]
+   */
+  parseInputObjectTypeExtension(): InputObjectTypeExtensionNode;
+
+  /**
+   * DirectiveDefinition :
+   *   - Description? directive @ Name ArgumentsDefinition? `repeatable`? on DirectiveLocations
+   */
+  parseDirectiveDefinition(): DirectiveDefinitionNode;
+
+  /**
+   * DirectiveLocations :
+   *   - `|`? DirectiveLocation
+   *   - DirectiveLocations | DirectiveLocation
+   */
+  parseDirectiveLocations(): Array<NameNode>;
+  parseDirectiveLocation(): NameNode;
+
+  /**
+   * Returns a location object, used to identify the place in the source that created a given parsed object.
+   */
+  loc(startToken: Token): Location | undefined;
+
+  /**
+   * Determines if the next token is of a given kind
+   */
+  peek(kind: TokenKindEnum): boolean;
+
+  /**
+   * If the next token is of the given kind, return that token after advancing the lexer.
+   * Otherwise, do not change the parser state and throw an error.
+   */
+  expectToken(kind: TokenKindEnum): Token;
+
+  /**
+   * If the next token is of the given kind, return that token after advancing the lexer.
+   * Otherwise, do not change the parser state and return undefined.
+   */
+  expectOptionalToken(kind: TokenKindEnum): Maybe<Token>;
+
+  /**
+   * If the next token is a given keyword, advance the lexer.
+   * Otherwise, do not change the parser state and throw an error.
+   */
+  expectKeyword(value: string): void;
+
+  /**
+   * If the next token is a given keyword, return "true" after advancing the lexer.
+   * Otherwise, do not change the parser state and return "false".
+   */
+  expectOptionalKeyword(value: string): boolean;
+
+  /**
+   * Helper function for creating an error when an unexpected lexed token is encountered.
+   */
+  unexpected(atToken?: Maybe<Token>): GraphQLError;
+
+  /**
+   * Returns a possibly empty list of parse nodes, determined by the parseFn.
+   * This list begins with a lex token of openKind and ends with a lex token of closeKind.
+   * Advances the parser to the next lex token after the closing token.
+   */
+  any<T>(
+    openKind: TokenKindEnum,
+    parseFn: () => T,
+    closeKind: TokenKindEnum,
+  ): Array<T>;
+
+  /**
+   * Returns a list of parse nodes, determined by the parseFn.
+   * It can be empty only if open token is missing otherwise it will always return non-empty list
+   * that begins with a lex token of openKind and ends with a lex token of closeKind.
+   * Advances the parser to the next lex token after the closing token.
+   */
+  optionalMany<T>(
+    openKind: TokenKindEnum,
+    parseFn: () => T,
+    closeKind: TokenKindEnum,
+  ): Array<T>;
+
+  /**
+   * Returns a non-empty list of parse nodes, determined by the parseFn.
+   * This list begins with a lex token of openKind and ends with a lex token of closeKind.
+   * Advances the parser to the next lex token after the closing token.
+   */
+  many<T>(
+    openKind: TokenKindEnum,
+    parseFn: () => T,
+    closeKind: TokenKindEnum,
+  ): Array<T>;
+
+  /**
+   * Returns a non-empty list of parse nodes, determined by the parseFn.
+   * This list may begin with a lex token of delimiterKind followed by items separated by lex tokens of tokenKind.
+   * Advances the parser to the next lex token after last item in the list.
+   */
+  delimitedMany<T>(delimiterKind: TokenKindEnum, parseFn: () => T): Array<T>;
+}