diff --git a/src/execution/__tests__/executor-test.js b/src/execution/__tests__/executor-test.js
index 9a70425c258..88f88b27556 100644
--- a/src/execution/__tests__/executor-test.js
+++ b/src/execution/__tests__/executor-test.js
@@ -1054,7 +1054,7 @@ describe('Execute: Handles basic execution tasks', () => {
       errors: [
         {
           message:
-            'Expected value of type "SpecialType" but got: [object Object].',
+            'Expected value of type "SpecialType" but got: {value: "bar"}.',
           locations: [{ line: 1, column: 3 }],
           path: ['specials', 1],
         },
diff --git a/src/execution/__tests__/variables-test.js b/src/execution/__tests__/variables-test.js
index 52b6006a267..9a72069f580 100644
--- a/src/execution/__tests__/variables-test.js
+++ b/src/execution/__tests__/variables-test.js
@@ -371,7 +371,7 @@ describe('Execute: Handles inputs', () => {
             {
               message:
                 'Variable "$input" got invalid value ' +
-                '{"a":"foo","b":"bar","c":null}; ' +
+                '{a: "foo", b: "bar", c: null}; ' +
                 'Expected non-nullable type String! not to be null at value.c.',
               locations: [{ line: 2, column: 16 }],
             },
@@ -401,7 +401,7 @@ describe('Execute: Handles inputs', () => {
           errors: [
             {
               message:
-                'Variable "$input" got invalid value {"a":"foo","b":"bar"}; ' +
+                'Variable "$input" got invalid value {a: "foo", b: "bar"}; ' +
                 'Field value.c of required type String! was not provided.',
               locations: [{ line: 2, column: 16 }],
             },
@@ -421,13 +421,13 @@ describe('Execute: Handles inputs', () => {
           errors: [
             {
               message:
-                'Variable "$input" got invalid value {"na":{"a":"foo"}}; ' +
+                'Variable "$input" got invalid value {na: {a: "foo"}}; ' +
                 'Field value.na.c of required type String! was not provided.',
               locations: [{ line: 2, column: 18 }],
             },
             {
               message:
-                'Variable "$input" got invalid value {"na":{"a":"foo"}}; ' +
+                'Variable "$input" got invalid value {na: {a: "foo"}}; ' +
                 'Field value.nb of required type String! was not provided.',
               locations: [{ line: 2, column: 18 }],
             },
@@ -446,7 +446,7 @@ describe('Execute: Handles inputs', () => {
             {
               message:
                 'Variable "$input" got invalid value ' +
-                '{"a":"foo","b":"bar","c":"baz","extra":"dog"}; ' +
+                '{a: "foo", b: "bar", c: "baz", extra: "dog"}; ' +
                 'Field "extra" is not defined by type TestInputObject.',
               locations: [{ line: 2, column: 16 }],
             },
@@ -693,8 +693,8 @@ describe('Execute: Handles inputs', () => {
         errors: [
           {
             message:
-              'Variable "$value" got invalid value [1,2,3]; Expected type ' +
-              'String; String cannot represent an array value: [1,2,3]',
+              'Variable "$value" got invalid value [1, 2, 3]; Expected type ' +
+              'String; String cannot represent an array value: [1, 2, 3]',
             locations: [{ line: 2, column: 16 }],
           },
         ],
@@ -841,7 +841,7 @@ describe('Execute: Handles inputs', () => {
         errors: [
           {
             message:
-              'Variable "$input" got invalid value ["A",null,"B"]; ' +
+              'Variable "$input" got invalid value ["A", null, "B"]; ' +
               'Expected non-nullable type String! not to be null at value[1].',
             locations: [{ line: 2, column: 16 }],
           },
@@ -891,7 +891,7 @@ describe('Execute: Handles inputs', () => {
         errors: [
           {
             message:
-              'Variable "$input" got invalid value ["A",null,"B"]; ' +
+              'Variable "$input" got invalid value ["A", null, "B"]; ' +
               'Expected non-nullable type String! not to be null at value[1].',
             locations: [{ line: 2, column: 16 }],
           },
diff --git a/src/execution/execute.js b/src/execution/execute.js
index fb04bd6f36f..cf557c18a88 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -1046,7 +1046,7 @@ function ensureValidRuntimeType(
     throw new GraphQLError(
       `Abstract type ${returnType.name} must resolve to an Object type at ` +
         `runtime for field ${info.parentType.name}.${info.fieldName} with ` +
-        `value "${inspect(result)}", received "${inspect(runtimeType)}". ` +
+        `value ${inspect(result)}, received "${inspect(runtimeType)}". ` +
         `Either the ${returnType.name} type should provide a "resolveType" ` +
         'function or each possible types should provide an ' +
         '"isTypeOf" function.',
diff --git a/src/execution/values.js b/src/execution/values.js
index 5df24406789..426faac4ab6 100644
--- a/src/execution/values.js
+++ b/src/execution/values.js
@@ -99,7 +99,7 @@ export function getVariableValues(
             coercionErrors.forEach(error => {
               error.message =
                 `Variable "$${varName}" got invalid ` +
-                `value ${JSON.stringify(value)}; ${error.message}`;
+                `value ${inspect(value)}; ${error.message}`;
             });
             errors.push(...coercionErrors);
           } else {
diff --git a/src/jsutils/inspect.js b/src/jsutils/inspect.js
index 70bc6bd21d3..2de18f1e05d 100644
--- a/src/jsutils/inspect.js
+++ b/src/jsutils/inspect.js
@@ -7,9 +7,21 @@
  * @flow strict
  */
 
+/**
+ * Used to print values in error messages.
+ */
 export default function inspect(value: mixed): string {
-  if (Array.isArray(value)) {
-    return '[' + String(value) + ']';
-  }
-  return String(value);
+  return Array.isArray(value)
+    ? '[' + value.map(inspect).join(', ') + ']'
+    : value && typeof value === 'object'
+      ? typeof value.inspect === 'function'
+        ? value.inspect()
+        : '{' +
+          Object.keys(value)
+            .map(k => `${k}: ${inspect(value[k])}`)
+            .join(', ') +
+          '}'
+      : typeof value === 'string'
+        ? '"' + value + '"'
+        : String(value);
 }
diff --git a/src/language/__tests__/parser-test.js b/src/language/__tests__/parser-test.js
index 620ec841de6..76fb9fefd35 100644
--- a/src/language/__tests__/parser-test.js
+++ b/src/language/__tests__/parser-test.js
@@ -29,9 +29,7 @@ describe('Parser', () => {
   });
 
   it('asserts that a source to parse was provided', () => {
-    expect(() => parse({})).to.throw(
-      'Must provide Source. Received: [object Object]',
-    );
+    expect(() => parse({})).to.throw('Must provide Source. Received: {}');
   });
 
   it('parse provides useful errors', () => {
diff --git a/src/subscription/__tests__/subscribe-test.js b/src/subscription/__tests__/subscribe-test.js
index 06a4d9e50f0..45f5addb1b8 100644
--- a/src/subscription/__tests__/subscribe-test.js
+++ b/src/subscription/__tests__/subscribe-test.js
@@ -373,7 +373,7 @@ describe('Subscription Initialization Phase', () => {
 
     await expectPromiseToThrow(
       () => createSubscription(pubsub, invalidEmailSchema),
-      'Subscription field must return Async Iterable. Received: test',
+      'Subscription field must return Async Iterable. Received: "test"',
     );
   });
 
@@ -474,7 +474,7 @@ describe('Subscription Initialization Phase', () => {
         {
           message:
             'Variable "$priority" got invalid value "meow"; Expected ' +
-            'type Int; Int cannot represent non-integer value: meow',
+            'type Int; Int cannot represent non-integer value: "meow"',
           locations: [{ line: 2, column: 21 }],
         },
       ],
diff --git a/src/type/__tests__/definition-test.js b/src/type/__tests__/definition-test.js
index 610c8112f31..f5f1d28a6a8 100644
--- a/src/type/__tests__/definition-test.js
+++ b/src/type/__tests__/definition-test.js
@@ -23,6 +23,7 @@ import {
 import { describe, it } from 'mocha';
 import { expect } from 'chai';
 
+import inspect from '../../jsutils/inspect';
 import { isObjectType, isInputType, isOutputType } from '../definition';
 
 const BlogImage = new GraphQLObjectType({
@@ -657,7 +658,7 @@ describe('Type System: Object fields must have valid resolve values', () => {
   it('rejects an empty Object field resolver', () => {
     expect(() => schemaWithObjectWithFieldResolver({})).to.throw(
       'BadResolver.badField field resolver must be a function if provided, ' +
-        'but got: [object Object].',
+        'but got: {}.',
     );
   });
 
@@ -1139,7 +1140,7 @@ describe('Type System: List must accept only types', () => {
   notTypes.forEach(type => {
     it(`rejects a non-type as item type of list: ${type}`, () => {
       expect(() => GraphQLList(type)).to.throw(
-        `Expected ${type} to be a GraphQL type.`,
+        `Expected ${inspect(type)} to be a GraphQL type.`,
       );
     });
   });
@@ -1175,7 +1176,7 @@ describe('Type System: NonNull must only accept non-nullable types', () => {
   notNullableTypes.forEach(type => {
     it(`rejects a non-type as nullable type of non-null: ${type}`, () => {
       expect(() => GraphQLNonNull(type)).to.throw(
-        `Expected ${type} to be a GraphQL nullable type.`,
+        `Expected ${inspect(type)} to be a GraphQL nullable type.`,
       );
     });
   });
diff --git a/src/type/__tests__/enumType-test.js b/src/type/__tests__/enumType-test.js
index 3763a2249ee..ab6eca14b89 100644
--- a/src/type/__tests__/enumType-test.js
+++ b/src/type/__tests__/enumType-test.js
@@ -205,7 +205,7 @@ describe('Type System: Enum Values', () => {
       data: { colorEnum: null },
       errors: [
         {
-          message: 'Expected a value of type "Color" but received: GREEN',
+          message: 'Expected a value of type "Color" but received: "GREEN"',
           locations: [{ line: 1, column: 3 }],
           path: ['colorEnum'],
         },
@@ -384,7 +384,7 @@ describe('Type System: Enum Values', () => {
       errors: [
         {
           message:
-            'Expected a value of type "Complex" but received: [object Object]',
+            'Expected a value of type "Complex" but received: {someRandomValue: 123}',
           locations: [{ line: 6, column: 9 }],
           path: ['bad'],
         },
diff --git a/src/type/__tests__/serialization-test.js b/src/type/__tests__/serialization-test.js
index ad0f618ef17..d6bf307a9db 100644
--- a/src/type/__tests__/serialization-test.js
+++ b/src/type/__tests__/serialization-test.js
@@ -38,7 +38,7 @@ describe('Type System: Scalar coercion', () => {
       'Int cannot represent non-integer value: -1.1',
     );
     expect(() => GraphQLInt.serialize('-1.1')).to.throw(
-      'Int cannot represent non-integer value: -1.1',
+      'Int cannot represent non-integer value: "-1.1"',
     );
     // Maybe a safe JavaScript int, but bigger than 2^32, so not
     // representable as a GraphQL Int
@@ -56,7 +56,7 @@ describe('Type System: Scalar coercion', () => {
       'Int cannot represent non 32-bit signed integer value: -1e+100',
     );
     expect(() => GraphQLInt.serialize('one')).to.throw(
-      'Int cannot represent non-integer value: one',
+      'Int cannot represent non-integer value: "one"',
     );
     // Doesn't represent number
     expect(() => GraphQLInt.serialize('')).to.throw(
@@ -92,7 +92,7 @@ describe('Type System: Scalar coercion', () => {
       'Float cannot represent non numeric value: Infinity',
     );
     expect(() => GraphQLFloat.serialize('one')).to.throw(
-      'Float cannot represent non numeric value: one',
+      'Float cannot represent non numeric value: "one"',
     );
     expect(() => GraphQLFloat.serialize('')).to.throw(
       'Float cannot represent non numeric value: (empty string)',
diff --git a/src/type/__tests__/validation-test.js b/src/type/__tests__/validation-test.js
index c1d328582ae..e290267380d 100644
--- a/src/type/__tests__/validation-test.js
+++ b/src/type/__tests__/validation-test.js
@@ -383,7 +383,7 @@ describe('Type System: A Schema must have Object root types', () => {
     });
     expect(validateSchema(schema)).to.deep.equal([
       {
-        message: 'Expected directive but got: somedirective.',
+        message: 'Expected directive but got: "somedirective".',
       },
     ]);
   });
diff --git a/src/utilities/__tests__/coerceValue-test.js b/src/utilities/__tests__/coerceValue-test.js
index d23f0341f5d..7adb1155da0 100644
--- a/src/utilities/__tests__/coerceValue-test.js
+++ b/src/utilities/__tests__/coerceValue-test.js
@@ -35,7 +35,7 @@ describe('coerceValue', () => {
       it('returns error for array input as string', () => {
         const result = coerceValue([1, 2, 3], scalar);
         expectErrors(result).to.deep.equal([
-          `Expected type ${scalar}; String cannot represent an array value: [1,2,3]`,
+          `Expected type ${scalar}; String cannot represent an array value: [1, 2, 3]`,
         ]);
       });
     });
@@ -79,7 +79,7 @@ describe('coerceValue', () => {
     it('returns a single error for float input as int', () => {
       const result = coerceValue('1.5', GraphQLInt);
       expectErrors(result).to.deep.equal([
-        'Expected type Int; Int cannot represent non-integer value: 1.5',
+        'Expected type Int; Int cannot represent non-integer value: "1.5"',
       ]);
     });
 
@@ -100,14 +100,14 @@ describe('coerceValue', () => {
     it('returns a single error for char input', () => {
       const result = coerceValue('a', GraphQLInt);
       expectErrors(result).to.deep.equal([
-        'Expected type Int; Int cannot represent non-integer value: a',
+        'Expected type Int; Int cannot represent non-integer value: "a"',
       ]);
     });
 
     it('returns a single error for char input', () => {
       const result = coerceValue('meow', GraphQLInt);
       expectErrors(result).to.deep.equal([
-        'Expected type Int; Int cannot represent non-integer value: meow',
+        'Expected type Int; Int cannot represent non-integer value: "meow"',
       ]);
     });
   });
@@ -157,14 +157,14 @@ describe('coerceValue', () => {
     it('returns a single error for char input', () => {
       const result = coerceValue('a', GraphQLFloat);
       expectErrors(result).to.deep.equal([
-        'Expected type Float; Float cannot represent non numeric value: a',
+        'Expected type Float; Float cannot represent non numeric value: "a"',
       ]);
     });
 
     it('returns a single error for char input', () => {
       const result = coerceValue('meow', GraphQLFloat);
       expectErrors(result).to.deep.equal([
-        'Expected type Float; Float cannot represent non numeric value: meow',
+        'Expected type Float; Float cannot represent non numeric value: "meow"',
       ]);
     });
   });
@@ -226,15 +226,15 @@ describe('coerceValue', () => {
     it('returns no error for an invalid field', () => {
       const result = coerceValue({ foo: 'abc' }, TestInputObject);
       expectErrors(result).to.deep.equal([
-        'Expected type Int at value.foo; Int cannot represent non-integer value: abc',
+        'Expected type Int at value.foo; Int cannot represent non-integer value: "abc"',
       ]);
     });
 
     it('returns multiple errors for multiple invalid fields', () => {
       const result = coerceValue({ foo: 'abc', bar: 'def' }, TestInputObject);
       expectErrors(result).to.deep.equal([
-        'Expected type Int at value.foo; Int cannot represent non-integer value: abc',
-        'Expected type Int at value.bar; Int cannot represent non-integer value: def',
+        'Expected type Int at value.foo; Int cannot represent non-integer value: "abc"',
+        'Expected type Int at value.bar; Int cannot represent non-integer value: "def"',
       ]);
     });
 
diff --git a/src/validation/rules/FragmentsOnCompositeTypes.js b/src/validation/rules/FragmentsOnCompositeTypes.js
index 9d285348ef0..6f2e0b87f57 100644
--- a/src/validation/rules/FragmentsOnCompositeTypes.js
+++ b/src/validation/rules/FragmentsOnCompositeTypes.js
@@ -7,28 +7,24 @@
  * @flow strict
  */
 
-import inspect from '../../jsutils/inspect';
 import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import { print } from '../../language/printer';
 import type { ASTVisitor } from '../../language/visitor';
 import { isCompositeType } from '../../type/definition';
-import type { GraphQLType } from '../../type/definition';
 import { typeFromAST } from '../../utilities/typeFromAST';
 
-export function inlineFragmentOnNonCompositeErrorMessage(
-  type: GraphQLType,
-): string {
-  return `Fragment cannot condition on non composite type "${inspect(type)}".`;
+export function inlineFragmentOnNonCompositeErrorMessage(type: string): string {
+  return `Fragment cannot condition on non composite type "${type}".`;
 }
 
 export function fragmentOnNonCompositeErrorMessage(
   fragName: string,
-  type: GraphQLType,
+  type: string,
 ): string {
   return (
     `Fragment "${fragName}" cannot condition on non composite ` +
-    `type "${inspect(type)}".`
+    `type "${type}".`
   );
 }
 
diff --git a/src/validation/rules/PossibleFragmentSpreads.js b/src/validation/rules/PossibleFragmentSpreads.js
index 95ee3212a9e..4461d5aeb33 100644
--- a/src/validation/rules/PossibleFragmentSpreads.js
+++ b/src/validation/rules/PossibleFragmentSpreads.js
@@ -14,26 +14,25 @@ import type { ASTVisitor } from '../../language/visitor';
 import { doTypesOverlap } from '../../utilities/typeComparators';
 import { typeFromAST } from '../../utilities/typeFromAST';
 import { isCompositeType } from '../../type/definition';
-import type { GraphQLType } from '../../type/definition';
 
 export function typeIncompatibleSpreadMessage(
   fragName: string,
-  parentType: GraphQLType,
-  fragType: GraphQLType,
+  parentType: string,
+  fragType: string,
 ): string {
   return (
     `Fragment "${fragName}" cannot be spread here as objects of ` +
-    `type "${inspect(parentType)}" can never be of type "${inspect(fragType)}".`
+    `type "${parentType}" can never be of type "${fragType}".`
   );
 }
 
 export function typeIncompatibleAnonSpreadMessage(
-  parentType: GraphQLType,
-  fragType: GraphQLType,
+  parentType: string,
+  fragType: string,
 ): string {
   return (
     'Fragment cannot be spread here as objects of ' +
-    `type "${inspect(parentType)}" can never be of type "${inspect(fragType)}".`
+    `type "${parentType}" can never be of type "${fragType}".`
   );
 }
 
@@ -58,7 +57,10 @@ export function PossibleFragmentSpreads(
       ) {
         context.reportError(
           new GraphQLError(
-            typeIncompatibleAnonSpreadMessage(parentType, fragType),
+            typeIncompatibleAnonSpreadMessage(
+              inspect(parentType),
+              inspect(fragType),
+            ),
             [node],
           ),
         );
@@ -75,7 +77,11 @@ export function PossibleFragmentSpreads(
       ) {
         context.reportError(
           new GraphQLError(
-            typeIncompatibleSpreadMessage(fragName, parentType, fragType),
+            typeIncompatibleSpreadMessage(
+              fragName,
+              inspect(parentType),
+              inspect(fragType),
+            ),
             [node],
           ),
         );
diff --git a/src/validation/rules/ProvidedRequiredArguments.js b/src/validation/rules/ProvidedRequiredArguments.js
index b6b60a09bb3..9c4f26904cb 100644
--- a/src/validation/rules/ProvidedRequiredArguments.js
+++ b/src/validation/rules/ProvidedRequiredArguments.js
@@ -12,28 +12,27 @@ import { GraphQLError } from '../../error';
 import inspect from '../../jsutils/inspect';
 import keyMap from '../../jsutils/keyMap';
 import { isNonNullType } from '../../type/definition';
-import type { GraphQLType } from '../../type/definition';
 import type { ASTVisitor } from '../../language/visitor';
 
 export function missingFieldArgMessage(
   fieldName: string,
   argName: string,
-  type: GraphQLType,
+  type: string,
 ): string {
   return (
     `Field "${fieldName}" argument "${argName}" of type ` +
-    `"${inspect(type)}" is required but not provided.`
+    `"${type}" is required but not provided.`
   );
 }
 
 export function missingDirectiveArgMessage(
   directiveName: string,
   argName: string,
-  type: GraphQLType,
+  type: string,
 ): string {
   return (
     `Directive "@${directiveName}" argument "${argName}" of type ` +
-    `"${inspect(type)}" is required but not provided.`
+    `"${type}" is required but not provided.`
   );
 }
 
@@ -69,7 +68,7 @@ export function ProvidedRequiredArguments(
                 missingFieldArgMessage(
                   node.name.value,
                   argDef.name,
-                  argDef.type,
+                  inspect(argDef.type),
                 ),
                 [node],
               ),
@@ -101,7 +100,7 @@ export function ProvidedRequiredArguments(
                 missingDirectiveArgMessage(
                   node.name.value,
                   argDef.name,
-                  argDef.type,
+                  inspect(argDef.type),
                 ),
                 [node],
               ),
diff --git a/src/validation/rules/ScalarLeafs.js b/src/validation/rules/ScalarLeafs.js
index 85f8f38fb1c..ba2818d00a5 100644
--- a/src/validation/rules/ScalarLeafs.js
+++ b/src/validation/rules/ScalarLeafs.js
@@ -12,25 +12,24 @@ import type ValidationContext from '../ValidationContext';
 import { GraphQLError } from '../../error';
 import type { FieldNode } from '../../language/ast';
 import { getNamedType, isLeafType } from '../../type/definition';
-import type { GraphQLType } from '../../type/definition';
 import type { ASTVisitor } from '../../language/visitor';
 
 export function noSubselectionAllowedMessage(
   fieldName: string,
-  type: GraphQLType,
+  type: string,
 ): string {
   return (
     `Field "${fieldName}" must not have a selection since ` +
-    `type "${inspect(type)}" has no subfields.`
+    `type "${type}" has no subfields.`
   );
 }
 
 export function requiredSubselectionMessage(
   fieldName: string,
-  type: GraphQLType,
+  type: string,
 ): string {
   return (
-    `Field "${fieldName}" of type "${inspect(type)}" must have a ` +
+    `Field "${fieldName}" of type "${type}" must have a ` +
     `selection of subfields. Did you mean "${fieldName} { ... }"?`
   );
 }
@@ -51,7 +50,7 @@ export function ScalarLeafs(context: ValidationContext): ASTVisitor {
           if (selectionSet) {
             context.reportError(
               new GraphQLError(
-                noSubselectionAllowedMessage(node.name.value, type),
+                noSubselectionAllowedMessage(node.name.value, inspect(type)),
                 [selectionSet],
               ),
             );
@@ -59,7 +58,7 @@ export function ScalarLeafs(context: ValidationContext): ASTVisitor {
         } else if (!selectionSet) {
           context.reportError(
             new GraphQLError(
-              requiredSubselectionMessage(node.name.value, type),
+              requiredSubselectionMessage(node.name.value, inspect(type)),
               [node],
             ),
           );
diff --git a/src/validation/rules/VariablesInAllowedPosition.js b/src/validation/rules/VariablesInAllowedPosition.js
index 21c04d55700..b7eec382636 100644
--- a/src/validation/rules/VariablesInAllowedPosition.js
+++ b/src/validation/rules/VariablesInAllowedPosition.js
@@ -21,12 +21,12 @@ import type { GraphQLSchema } from '../../type/schema';
 
 export function badVarPosMessage(
   varName: string,
-  varType: GraphQLType,
-  expectedType: GraphQLType,
+  varType: string,
+  expectedType: string,
 ): string {
   return (
-    `Variable "$${varName}" of type "${inspect(varType)}" used in ` +
-    `position expecting type "${inspect(expectedType)}".`
+    `Variable "$${varName}" of type "${varType}" used in ` +
+    `position expecting type "${expectedType}".`
   );
 }
 
@@ -68,10 +68,10 @@ export function VariablesInAllowedPosition(
               )
             ) {
               context.reportError(
-                new GraphQLError(badVarPosMessage(varName, varType, type), [
-                  varDef,
-                  node,
-                ]),
+                new GraphQLError(
+                  badVarPosMessage(varName, inspect(varType), inspect(type)),
+                  [varDef, node],
+                ),
               );
             }
           }