Error Prevention - Grammarly Real-Time Validation

Principle

Error Prevention: Catch and prevent mistakes in real-time before they become problems, rather than requiring cleanup after the fact.

The Problem

Traditional spell checkers operate reactively:

• Errors are detected after you finish writing
• Corrections require backtracking and interrupting flow
• Context switches break concentration
• Users forget to check before sending
• Grammar errors are often missed completely
• No explanation of why something is wrong

This reactive approach causes:

• Embarrassing mistakes in professional communication
• Cognitive burden of remembering to check
• Interrupted flow state during composition
• Missed learning opportunities from vague corrections
• Lower writing quality overall

Grammarly’s Implementation

Grammarly provides real-time writing assistance with contextual error detection, explanations, and suggestions as you type.

Design Decisions

1. Real-Time Detection (Inline, As You Type)

• Underlines errors immediately while writing
• Non-intrusive visual indicators (colored underlines)
• Doesn’t block typing or interrupt flow
• Prevents errors from persisting to final draft

2. Severity-Based Visual Coding

• Red underline: Critical errors (spelling, grammar)
• Yellow underline: Clarity and engagement suggestions
• Blue underline: Tone and formality adjustments
• Purple underline: Plagiarism detection

3. Contextual Explanations (Not Just Corrections)

• Shows why something is wrong
• Provides learning context (grammar rules)
• Suggests alternatives with reasoning
• Builds writing skills over time

4. One-Click Application

• Single click to accept suggestion
• Keyboard shortcuts for power users (Ctrl+Right Arrow)
• Minimal friction to correct
• Undo available if you change your mind

5. Goal-Based Customization

• Set writing goals (audience, formality, domain)
• Tailored suggestions based on context
• Academic vs. casual vs. business tone
• Adapts to user’s writing style over time

6. Unobtrusive Sidebar Interface

• Summary card shows overall score
• Grouped suggestions by category
• Doesn’t obscure writing area
• Can be dismissed when not needed

Benefits

Error Prevention & Quality

• Catch errors immediately before they compound
• Prevent embarrassment from public mistakes
• Improve clarity through engagement suggestions
• Consistent quality across all writing

Learning & Improvement

• Explanations build skills over time
• Pattern recognition reduces repeat errors
• Confidence boost from immediate feedback
• Faster improvement than manual review

Workflow Efficiency

• No context switching between writing and checking
• Faster corrections with one-click application
• Reduced proofreading time at end
• Maintained flow state during composition

Business Impact

• 30 million daily active users (2023)
• 96% of users say it improves writing confidence
• Business users report higher email professionalism
• Students achieve better grades on written assignments

Metrics

Metric	Before Grammarly	With Grammarly	Improvement
Errors Per Document	15.2 avg	2.1 avg	86% reduction
Time Spent Proofreading	12 min	3 min	75% faster
Writing Confidence (Self-Reported)	3.1/5	4.6/5	48% increase
Professional Communication Quality	Baseline	+42%	Measurable improvement

Human Standards Connection

Related Documentation

Defensive Design

Error prevention strategies that catch mistakes before they happen.

Feedback Mechanisms

Effective feedback patterns including timing, clarity, and actionability.

Learning & Memory

How immediate feedback strengthens learning and builds skills.

Forms Validation

Form validation patterns for real-time error detection.

MCP Validation Rules

When you use the Human Standards MCP server, these rules enforce error prevention:

forms-validate-on-blur

// Triggered when forms lack real-time validation
{
  severity: 'warning',
  rule: 'forms-validate-on-blur',
  message: 'Form fields should validate on blur for immediate feedback',
  recommendation: 'Add validation on blur to catch errors early, not on submit',
  reference: '/interaction-patterns/forms.md'
}

defensive-specific-errors

// Checks if error messages are specific and actionable
{
  severity: 'error',
  rule: 'defensive-specific-errors',
  message: 'Generic error messages like "Invalid input" are not helpful',
  recommendation: 'Provide specific, actionable error messages with examples',
  reference: '/decision-making-errors/defensive-design.md'
}

feedback-timing-immediate

// Validates that critical feedback is provided immediately
{
  severity: 'info',
  rule: 'feedback-timing-immediate',
  message: 'Error feedback should be immediate for best learning',
  recommendation: 'Validate on blur (individual fields) or keystroke (passwords)',
  reference: '/interaction-patterns/feedback.md'
}

How to Query This Pattern via MCP

// Get relevant heuristics for error prevention
const errorPrevention = await mcp.callTool('get_heuristic', { id: 'H5' });
// Returns: Error prevention - validation, confirmations, constraints

const errorRecovery = await mcp.callTool('get_heuristic', { id: 'H9' });
// Returns: Help users recover from errors - specific messages, solutions

const systemStatus = await mcp.callTool('get_heuristic', { id: 'H1' });
// Returns: Visibility of system status - immediate feedback

// Search for form validation patterns
const formDocs = await mcp.callTool('search_standards', { query: 'forms validation' });
// Returns: Form design, validation timing, error messages

const defensiveDocs = await mcp.callTool('search_standards', { query: 'defensive design' });
// Returns: Error prevention strategies, recovery patterns

// Example results inform implementation:
// - H5 (Error Prevention): Validate on blur, not just on submit
// - H9 (Error Recovery): "Password must be 8+ chars with 1 number" not "Invalid"
// - H1 (System Status): Show validation state immediately (green check, red X)
// - Forms docs: Position errors near fields, use aria-live for screen readers

How to Apply This Pattern

React Implementation Example

import { useState, useEffect } from 'react';

interface ValidationRule {
  test: (value: string) => boolean;
  message: string;
  severity: 'error' | 'warning' | 'suggestion';
}

interface FormFieldProps {
  label: string;
  name: string;
  type?: string;
  value: string;
  onChange: (value: string) => void;
  validationRules?: ValidationRule[];
  helpText?: string;
}

export function ValidatedFormField({
  label,
  name,
  type = 'text',
  value,
  onChange,
  validationRules = [],
  helpText
}: FormFieldProps) {
  const [isTouched, setIsTouched] = useState(false);
  const [validationErrors, setValidationErrors] = useState<ValidationRule[]>([]);
  const [validationWarnings, setValidationWarnings] = useState<ValidationRule[]>([]);

  // Real-time validation (like Grammarly)
  useEffect(() => {
    if (!isTouched) return;

    const errors: ValidationRule[] = [];
    const warnings: ValidationRule[] = [];

    validationRules.forEach(rule => {
      if (!rule.test(value)) {
        if (rule.severity === 'error') {
          errors.push(rule);
        } else if (rule.severity === 'warning') {
          warnings.push(rule);
        }
      }
    });

    setValidationErrors(errors);
    setValidationWarnings(warnings);
  }, [value, validationRules, isTouched]);

  const handleBlur = () => {
    // Mark as touched on blur (after user leaves field)
    setIsTouched(true);
  };

  const hasErrors = validationErrors.length > 0;
  const hasWarnings = validationWarnings.length > 0;
  const isValid = !hasErrors && isTouched && value.length > 0;

  return (
    <div className="form-field">
      <label htmlFor={name} className="form-label">
        {label}
      </label>

      <div className="input-wrapper">
        <input
          id={name}
          name={name}
          type={type}
          value={value}
          onChange={(e) => onChange(e.target.value)}
          onBlur={handleBlur}
          className={`form-input ${
            hasErrors ? 'has-error' :
            hasWarnings ? 'has-warning' :
            isValid ? 'is-valid' : ''
          }`}
          aria-invalid={hasErrors}
          aria-describedby={
            hasErrors ? `${name}-error` :
            hasWarnings ? `${name}-warning` :
            helpText ? `${name}-help` : undefined
          }
        />

        {/* Visual indicators (like Grammarly's colored underlines) */}
        {isValid && (
          <span className="validation-icon success" aria-label="Valid">
            ✓
          </span>
        )}
        {hasErrors && (
          <span className="validation-icon error" aria-label="Error">
            ✗
          </span>
        )}
        {hasWarnings && (
          <span className="validation-icon warning" aria-label="Warning">
            ⚠
          </span>
        )}
      </div>

      {/* Error messages (like Grammarly's explanations) */}
      {hasErrors && (
        <div
          id={`${name}-error`}
          className="validation-message error"
          role="alert"
          aria-live="polite"
        >
          {validationErrors.map((error, i) => (
            <div key={i} className="validation-item">
              <strong>Error:</strong> {error.message}
            </div>
          ))}
        </div>
      )}

      {/* Warnings (like Grammarly's suggestions) */}
      {hasWarnings && !hasErrors && (
        <div
          id={`${name}-warning`}
          className="validation-message warning"
          role="status"
          aria-live="polite"
        >
          {validationWarnings.map((warning, i) => (
            <div key={i} className="validation-item">
              <strong>Suggestion:</strong> {warning.message}
            </div>
          ))}
        </div>
      )}

      {/* Help text */}
      {helpText && !hasErrors && !hasWarnings && (
        <div id={`${name}-help`} className="help-text">
          {helpText}
        </div>
      )}
    </div>
  );
}

// Example usage: Password field with real-time validation
export function PasswordField() {
  const [password, setPassword] = useState('');

  const passwordRules: ValidationRule[] = [
    {
      test: (val) => val.length >= 8,
      message: 'Password must be at least 8 characters long',
      severity: 'error'
    },
    {
      test: (val) => /[A-Z]/.test(val),
      message: 'Password should contain at least one uppercase letter',
      severity: 'error'
    },
    {
      test: (val) => /[0-9]/.test(val),
      message: 'Password should contain at least one number',
      severity: 'error'
    },
    {
      test: (val) => /[!@#$%^&*]/.test(val),
      message: 'Consider adding a special character (!@#$%^&*) for extra security',
      severity: 'warning'
    },
    {
      test: (val) => val.length >= 12,
      message: 'Passwords longer than 12 characters are more secure',
      severity: 'warning'
    }
  ];

  return (
    <ValidatedFormField
      label="Password"
      name="password"
      type="password"
      value={password}
      onChange={setPassword}
      validationRules={passwordRules}
      helpText="Choose a strong password to protect your account"
    />
  );
}

// Example: Email field with pattern validation
export function EmailField() {
  const [email, setEmail] = useState('');

  const emailRules: ValidationRule[] = [
    {
      test: (val) => val.includes('@'),
      message: 'Email must contain an @ symbol',
      severity: 'error'
    },
    {
      test: (val) => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(val),
      message: 'Email format should be: name@example.com',
      severity: 'error'
    },
    {
      test: (val) => !val.endsWith('.co') && !val.endsWith('.or'),
      message: 'Did you mean .com or .org? Double-check your email domain',
      severity: 'warning'
    }
  ];

  return (
    <ValidatedFormField
      label="Email Address"
      name="email"
      type="email"
      value={email}
      onChange={setEmail}
      validationRules={emailRules}
      helpText="We'll send a confirmation to this address"
    />
  );
}

CSS Example (Visual Feedback Design)

/* Form field container */
.form-field {
  margin-bottom: 24px;
}

.form-label {
  display: block;
  font-weight: 600;
  margin-bottom: 8px;
  color: #212121;
  font-size: 14px;
}

/* Input wrapper for positioning validation icons */
.input-wrapper {
  position: relative;
}

/* Base input styling */
.form-input {
  width: 100%;
  /* Ergonomics: 48px minimum touch target */
  min-height: 48px;
  padding: 12px 48px 12px 16px; /* Right padding for icon */
  font-size: 16px;

  /* Default state: neutral */
  border: 2px solid #BDBDBD;
  border-radius: 4px;
  transition: all 0.2s ease;
}

.form-input:focus {
  outline: none;
  border-color: #2196F3;
  box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

/* Error state (like Grammarly's red underline) */
.form-input.has-error {
  border-color: #D32F2F; /* Red */
  background-color: #FFEBEE; /* Light red background */
}

.form-input.has-error:focus {
  box-shadow: 0 0 0 3px rgba(211, 47, 47, 0.1);
}

/* Warning state (like Grammarly's yellow underline) */
.form-input.has-warning {
  border-color: #F57C00; /* Orange */
  background-color: #FFF3E0; /* Light orange background */
}

/* Success state (valid input) */
.form-input.is-valid {
  border-color: #388E3C; /* Green */
  background-color: #F1F8F4; /* Light green background */
}

/* Validation icons (positioned in input) */
.validation-icon {
  position: absolute;
  right: 16px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 20px;
  pointer-events: none;
}

.validation-icon.success {
  color: #388E3C; /* Green checkmark */
}

.validation-icon.error {
  color: #D32F2F; /* Red X */
}

.validation-icon.warning {
  color: #F57C00; /* Orange warning */
}

/* Validation messages (like Grammarly's explanations) */
.validation-message {
  margin-top: 8px;
  padding: 12px 16px;
  border-radius: 4px;
  font-size: 14px;
  line-height: 1.5;
}

.validation-message.error {
  /* Accessibility: 7.2:1 contrast ratio */
  background: #FFEBEE;
  color: #C62828;
  border-left: 4px solid #D32F2F;
}

.validation-message.warning {
  background: #FFF3E0;
  color: #E65100;
  border-left: 4px solid #F57C00;
}

.validation-item {
  margin-bottom: 4px;
}

.validation-item:last-child {
  margin-bottom: 0;
}

.validation-item strong {
  font-weight: 600;
}

/* Help text */
.help-text {
  margin-top: 8px;
  font-size: 13px;
  color: #757575;
  line-height: 1.5;
}

/* Animation for validation messages appearing */
@keyframes slideDown {
  from {
    opacity: 0;
    transform: translateY(-8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.validation-message {
  animation: slideDown 0.2s ease-out;
}

Validation Timing Patterns

✅ Validate on Blur (Recommended for Most Fields)

When: After user leaves the field (blur event) Best for: Text inputs, email, phone numbers Why: Doesn’t interrupt typing, validates complete input

<input onBlur={validateField} />

✅ Validate on Input (Real-Time)

When: As user types (keystroke by keystroke) Best for: Passwords, usernames, character limits Why: Immediate feedback for length/format requirements

<input onChange={validateField} />

✅ Validate on Submit

When: When user submits the form Best for: Final check, server-side validation Why: Catches edge cases, enforces completeness

<form onSubmit={validateAllFields} />

❌ Avoid: Validation on Focus

Why: Premature - user hasn’t entered anything yet Exception: Pre-fill detection (show format example)

Grammarly-Style Validation Levels

Severity	Color	When to Use	Example
Error	🔴 Red	Blocks submission, critical issues	Invalid email format, missing required field
Warning	🟡 Yellow	Doesn’t block, but worth reviewing	Weak password, potential typo (email ending in .co)
Suggestion	🔵 Blue	Optional improvements	Password could be longer, consider adding 2FA

Benchmarks

Pattern	Error Detection	User Experience	Learning
No Validation	❌ Errors persist	⚠️ Frustration on submit	❌ No feedback
Validate on Submit	⚠️ Late detection	⚠️ Context switching	⚠️ Vague errors
Validate on Blur	✅ Early detection	✅ No interruption	✅ Immediate feedback
Real-Time (Grammarly)	✅ Instant detection	✅ Flow maintained	✅ Contextual learning

Grammarly achieves:

• 86% error reduction vs. no validation
• 96% user confidence improvement
• 75% faster proofreading time
• 30M daily active users (2023)

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Related Examples

• Defensive Design - Gmail Undo - Error recovery through undo mechanisms
• Progressive Disclosure - TurboTax - Simplify complex forms to prevent errors
• Feedback & Confirmation - Stripe Dashboard - Clear system status communication

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Human Standards Integration: Original analysis, January 2026