Eval Step

The Eval step executes custom JavaScript code within your flow. Use it for complex logic, custom calculations, advanced data manipulation, or anything that can’t be accomplished with other step types. Full JavaScript ES6+ support with access to common libraries.

Use Sparingly: Eval is powerful but adds complexity. Use built-in steps (Map, Rules, Functions) when possible. Reserve Eval for truly custom logic that can’t be accomplished otherwise.

How It Works

Eval executes JavaScript code and returns the result:

Previous Step: Order data
↓
Eval: Calculate complex pricing
  Code: Custom pricing algorithm
  Returns: Calculated price
↓
Next Step: Use calculated price

When to Use Eval

Use Eval When	Use Alternative When
Complex calculations beyond Rules	Simple math (use Rules)
Custom algorithms not available elsewhere	Standard operations (use Functions)
Advanced array/object manipulation beyond Map	Simple transforms (use Map)
Need specific JavaScript libraries	Built-in operators sufficient
Complex conditional logic with edge cases	Simple if/then (use Condition)
Prototyping new logic before building proper step	Logic is stable (build custom step)

Examples: ✅ Use Eval: Calculate compound interest with variable rates, fees, and payment schedules
❌ Use Rules instead: Simple percentage calculation ✅ Use Eval: Implement custom recommendation algorithm
❌ Use Agent instead: Interpret user needs and recommend ✅ Use Eval: Parse and validate complex data formats
❌ Use Map instead: Extract fields from JSON

Configuration

Code

code

string

required

JavaScript code to executeMust return a value using return statementAvailable variables:

input - Input data from previous step or trigger
context - Full flow context including all previous steps
trigger - Original trigger data
secrets - Access to secrets (read-only)

Example:

// Access input
const orderTotal = input.total;
const customerTier = input.tier;

// Access previous steps
const agentDecision = context.agent_step.output.decision;

// Perform calculations
let discount = 0;
if (customerTier === "gold" && orderTotal > 1000) {
  discount = orderTotal * 0.15;
} else if (customerTier === "silver" && orderTotal > 500) {
  discount = orderTotal * 0.10;
}

// Return result
return {
  discount: discount,
  finalPrice: orderTotal - discount,
  discountApplied: discount > 0
};

Input Data

input

any

Data passed to the Eval stepCan reference previous steps:

{
  "order": "${http_request.body}",
  "customer": "${customer_data}",
  "settings": "${config}"
}

Accessible in code as input object

Timeout

timeout

number

default:"5000"

Maximum execution time in millisecondsRecommendations:

Simple logic: 1000ms (1 second)
Moderate complexity: 5000ms (5 seconds, default)
Heavy processing: 30000ms (30 seconds)

Long timeouts can slow flows. Optimize code for performance.

Available Libraries

Eval has access to common JavaScript libraries:

Lodash

Utility library for arrays, objects, and moreImport:

const _ = require('lodash');

Common uses:

// Group array by property
const grouped = _.groupBy(items, 'category');

// Deep clone object
const copy = _.cloneDeep(original);

// Get nested value safely
const value = _.get(object, 'deep.nested.path', 'default');

// Debounce/throttle (for async operations)
const debounced = _.debounce(fn, 1000);

Moment.js

Date and time manipulationImport:

const moment = require('moment');

Common uses:

// Parse and format dates
const date = moment('2025-10-16').format('MMMM DD, YYYY');

// Add/subtract time
const tomorrow = moment().add(1, 'days');

// Compare dates
const isBefore = moment(date1).isBefore(date2);

// Calculate duration
const duration = moment.duration(end.diff(start));
const hours = duration.asHours();

Math.js

Advanced mathematical operationsImport:

const math = require('mathjs');

Common uses:

// Complex calculations
const result = math.evaluate('sqrt(3^2 + 4^2)');

// Matrix operations
const matrix = math.matrix([[1, 2], [3, 4]]);

// Statistical functions
const mean = math.mean([1, 2, 3, 4, 5]);
const stdDev = math.std([1, 2, 3, 4, 5]);

Crypto (Node.js)

Cryptographic functionsImport:

const crypto = require('crypto');

Common uses:

// Generate hash
const hash = crypto.createHash('sha256')
  .update(data)
  .digest('hex');

// Generate random values
const randomBytes = crypto.randomBytes(16).toString('hex');

// HMAC signature
const hmac = crypto.createHmac('sha256', secret)
  .update(data)
  .digest('hex');

Standard JavaScript

All standard ES6+ features availableIncludes:

Array methods (map, filter, reduce, find, etc.)
Object methods (keys, values, entries, assign, etc.)
String methods (split, replace, match, etc.)
Math object (round, floor, ceil, random, etc.)
JSON parse/stringify
RegExp for pattern matching
Promises and async/await
Template literals
Destructuring
Spread operator

Common Patterns

Complex Calculations

Calculations beyond simple operators

// Compound interest calculation
const principal = input.amount;
const rate = input.annual_rate / 100;
const years = input.term_years;
const compoundFreq = 12; // monthly

const amount = principal * Math.pow(
  (1 + rate / compoundFreq),
  compoundFreq * years
);

const totalInterest = amount - principal;

return {
  principal: principal,
  final_amount: Math.round(amount * 100) / 100,
  total_interest: Math.round(totalInterest * 100) / 100,
  monthly_payment: Math.round((amount / (years * 12)) * 100) / 100
};

Advanced Array Processing

Complex array manipulation beyond Map

const orders = input.orders;

// Group by customer, calculate totals, filter high-value
const _ = require('lodash');

const customerTotals = _.chain(orders)
  .groupBy('customer_id')
  .map((orders, customerId) => ({
    customer_id: customerId,
    order_count: orders.length,
    total_spent: _.sumBy(orders, 'amount'),
    avg_order: _.meanBy(orders, 'amount'),
    last_order_date: _.maxBy(orders, 'date').date
  }))
  .filter(c => c.total_spent > 10000)
  .orderBy(['total_spent'], ['desc'])
  .value();

return {
  high_value_customers: customerTotals,
  count: customerTotals.length
};

Data Validation

Custom validation logic

const data = input;
const errors = [];

// Email validation
const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
if (!emailRegex.test(data.email)) {
  errors.push("Invalid email format");
}

// Phone validation (US format)
const phoneRegex = /^\d{3}-\d{3}-\d{4}$/;
if (!phoneRegex.test(data.phone)) {
  errors.push("Phone must be format: XXX-XXX-XXXX");
}

// Age validation
const age = new Date().getFullYear() - new Date(data.birthdate).getFullYear();
if (age < 18) {
  errors.push("Must be 18 or older");
}

// Custom business rule
if (data.loan_amount > data.annual_income * 5) {
  errors.push("Loan amount cannot exceed 5x annual income");
}

return {
  valid: errors.length === 0,
  errors: errors,
  data: data
};

String Parsing and Formatting

Complex string manipulation

const text = input.raw_text;

// Extract email addresses
const emailRegex = /[^\s@]+@[^\s@]+\.[^\s@]+/g;
const emails = text.match(emailRegex) || [];

// Extract phone numbers (various formats)
const phoneRegex = /(\d{3}[-.]?\d{3}[-.]?\d{4})/g;
const phones = text.match(phoneRegex) || [];

// Extract URLs
const urlRegex = /(https?:\/\/[^\s]+)/g;
const urls = text.match(urlRegex) || [];

// Clean and format
const cleaned = text
  .toLowerCase()
  .trim()
  .replace(/\s+/g, ' ')
  .replace(/[^\w\[email protected]]/g, '');

return {
  original: text,
  cleaned: cleaned,
  extracted: {
    emails: emails,
    phones: phones,
    urls: urls
  }
};

Date/Time Calculations

Complex date logic

const moment = require('moment');

const startDate = moment(input.start_date);
const endDate = moment(input.end_date);

// Calculate business days (exclude weekends)
let businessDays = 0;
let current = startDate.clone();

while (current.isSameOrBefore(endDate)) {
  if (current.day() !== 0 && current.day() !== 6) {
    businessDays++;
  }
  current.add(1, 'days');
}

// Calculate age
const birthdate = moment(input.birthdate);
const age = moment().diff(birthdate, 'years');

// Format various ways
return {
  business_days: businessDays,
  total_days: endDate.diff(startDate, 'days'),
  weeks: endDate.diff(startDate, 'weeks'),
  age: age,
  formatted_start: startDate.format('MMMM DD, YYYY'),
  formatted_end: endDate.format('MMMM DD, YYYY')
};

Conditional Logic with Edge Cases

Complex business logic with many conditions

const customer = input.customer;
const order = input.order;

let tier = "standard";
let discount = 0;
let shippingFee = 9.99;
let priority = "normal";

// Determine tier
if (customer.lifetime_value > 50000) {
  tier = "platinum";
} else if (customer.lifetime_value > 10000) {
  tier = "gold";
} else if (customer.lifetime_value > 1000) {
  tier = "silver";
}

// Calculate discount (complex rules)
if (tier === "platinum") {
  discount = 0.20;
  shippingFee = 0;
  priority = "high";
} else if (tier === "gold" && order.total > 500) {
  discount = 0.15;
  shippingFee = 0;
} else if (tier === "silver" && order.total > 200) {
  discount = 0.10;
} else if (order.total > 100) {
  discount = 0.05;
}

// Special promotions
if (customer.referred_by && order.is_first) {
  discount = Math.max(discount, 0.10); // At least 10% for referrals
}

// Edge cases
if (customer.account_on_hold) {
  return {
    approved: false,
    reason: "Account on hold - contact support"
  };
}

if (order.shipping_country !== customer.billing_country) {
  priority = "review"; // Flag for fraud review
}

// Calculate final pricing
const subtotal = order.total;
const discountAmount = subtotal * discount;
const total = subtotal - discountAmount + shippingFee;

return {
  approved: true,
  tier: tier,
  discount_percent: discount * 100,
  discount_amount: Math.round(discountAmount * 100) / 100,
  shipping_fee: shippingFee,
  subtotal: subtotal,
  total: Math.round(total * 100) / 100,
  priority: priority
};

API Response Transformation

Complex data reshaping beyond Map

const apiData = input.api_response;
const _ = require('lodash');

// Transform deeply nested API response
const users = apiData.data.users.map(user => {
  // Extract and flatten
  const orders = _.get(user, 'relationships.orders.data', []);
  const orderDetails = orders.map(order => ({
    id: order.id,
    amount: _.get(order, 'attributes.total_amount', 0),
    status: _.get(order, 'attributes.status', 'unknown'),
    date: _.get(order, 'attributes.created_at')
  }));
  
  // Calculate aggregates
  const totalSpent = _.sumBy(orderDetails, 'amount');
  const orderCount = orderDetails.length;
  const lastOrderDate = _.maxBy(orderDetails, 'date')?.date;
  
  return {
    id: user.id,
    name: _.get(user, 'attributes.name'),
    email: _.get(user, 'attributes.email'),
    created: _.get(user, 'attributes.created_at'),
    stats: {
      total_spent: totalSpent,
      order_count: orderCount,
      avg_order: orderCount > 0 ? totalSpent / orderCount : 0,
      last_order: lastOrderDate
    },
    orders: orderDetails
  };
});

return {
  users: users,
  total_count: users.length,
  high_value_count: users.filter(u => u.stats.total_spent > 10000).length
};

Custom Scoring Algorithm

Proprietary scoring logic

const lead = input.lead;
let score = 0;
const factors = [];

// Company size scoring (0-30 points)
if (lead.company_employees >= 1000) {
  score += 30;
  factors.push({factor: "company_size", points: 30, value: "1000+"});
} else if (lead.company_employees >= 100) {
  score += 20;
  factors.push({factor: "company_size", points: 20, value: "100-999"});
} else {
  score += 10;
  factors.push({factor: "company_size", points: 10, value: "<100"});
}

// Budget scoring (0-30 points)
if (lead.budget >= 100000) {
  score += 30;
  factors.push({factor: "budget", points: 30, value: "$100k+"});
} else if (lead.budget >= 50000) {
  score += 20;
  factors.push({factor: "budget", points: 20, value: "$50k-100k"});
} else {
  score += 10;
  factors.push({factor: "budget", points: 10, value: "<$50k"});
}

// Industry fit (0-20 points)
const targetIndustries = ["technology", "finance", "healthcare"];
if (targetIndustries.includes(lead.industry.toLowerCase())) {
  score += 20;
  factors.push({factor: "industry", points: 20, value: "target industry"});
}

// Engagement scoring (0-20 points)
const engagementScore = Math.min(20, 
  (lead.website_visits * 2) + 
  (lead.email_opens * 1) + 
  (lead.demo_requests * 5)
);
score += engagementScore;
factors.push({factor: "engagement", points: engagementScore, value: "activity"});

// Decision maker bonus (10 points)
const decisionMakers = ["ceo", "cto", "cfo", "vp", "director"];
if (decisionMakers.some(role => lead.title.toLowerCase().includes(role))) {
  score += 10;
  factors.push({factor: "decision_maker", points: 10, value: lead.title});
}

// Determine tier
let tier;
if (score >= 80) tier = "hot";
else if (score >= 60) tier = "warm";
else if (score >= 40) tier = "cold";
else tier = "unqualified";

return {
  score: score,
  tier: tier,
  factors: factors,
  lead_id: lead.id,
  recommendation: tier === "hot" ? "contact immediately" : 
                  tier === "warm" ? "nurture sequence" : 
                  tier === "cold" ? "standard follow-up" : 
                  "disqualify"
};

Real-World Examples

Example 1: Mortgage Qualification Calculator

const applicant = input.applicant;
const property = input.property;

// Constants
const MAX_DTI = 0.43; // Max debt-to-income ratio
const MIN_CREDIT_SCORE = 620;
const MAX_LTV = 0.80; // Max loan-to-value

// Calculate debt-to-income ratio
const monthlyIncome = applicant.annual_income / 12;
const monthlyDebts = applicant.monthly_debt_payments;
const estimatedMortgage = (property.price * 0.8) * 0.005; // Rough estimate
const totalMonthlyDebt = monthlyDebts + estimatedMortgage;
const dti = totalMonthlyDebt / monthlyIncome;

// Calculate loan-to-value
const downPayment = property.down_payment;
const loanAmount = property.price - downPayment;
const ltv = loanAmount / property.price;

// Check qualifications
const qualified = 
  applicant.credit_score >= MIN_CREDIT_SCORE &&
  dti <= MAX_DTI &&
  ltv <= MAX_LTV &&
  applicant.employment_years >= 2;

// Calculate interest rate (simplified)
let interestRate;
if (applicant.credit_score >= 760 && ltv <= 0.7) {
  interestRate = 0.065;
} else if (applicant.credit_score >= 720) {
  interestRate = 0.070;
} else if (applicant.credit_score >= 680) {
  interestRate = 0.075;
} else {
  interestRate = 0.080;
}

// Calculate monthly payment
const monthlyRate = interestRate / 12;
const numPayments = 30 * 12; // 30-year mortgage
const monthlyPayment = loanAmount * 
  (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) /
  (Math.pow(1 + monthlyRate, numPayments) - 1);

// Reasons for disqualification
const reasons = [];
if (applicant.credit_score < MIN_CREDIT_SCORE) {
  reasons.push(`Credit score too low (${applicant.credit_score} < ${MIN_CREDIT_SCORE})`);
}
if (dti > MAX_DTI) {
  reasons.push(`Debt-to-income ratio too high (${(dti * 100).toFixed(1)}% > ${MAX_DTI * 100}%)`);
}
if (ltv > MAX_LTV) {
  reasons.push(`Loan-to-value too high (${(ltv * 100).toFixed(1)}% > ${MAX_LTV * 100}%)`);
}
if (applicant.employment_years < 2) {
  reasons.push(`Insufficient employment history (${applicant.employment_years} years < 2 years)`);
}

return {
  qualified: qualified,
  reasons: reasons,
  details: {
    loan_amount: Math.round(loanAmount),
    interest_rate: interestRate,
    monthly_payment: Math.round(monthlyPayment),
    dti_ratio: Math.round(dti * 1000) / 10,
    ltv_ratio: Math.round(ltv * 1000) / 10,
    total_interest: Math.round((monthlyPayment * numPayments) - loanAmount)
  }
};

Example 2: Recommendation Engine

const _ = require('lodash');

const user = input.user;
const products = input.products;
const userHistory = input.purchase_history;

// Calculate user preferences from history
const categoryPreferences = _.chain(userHistory)
  .groupBy('category')
  .mapValues(items => ({
    count: items.length,
    avg_rating: _.meanBy(items, 'rating'),
    total_spent: _.sumBy(items, 'price')
  }))
  .value();

// Score each product
const scoredProducts = products.map(product => {
  let score = 0;
  
  // Category preference (0-40 points)
  const categoryPref = categoryPreferences[product.category];
  if (categoryPref) {
    score += Math.min(40, categoryPref.count * 5);
  }
  
  // Price fit (0-20 points)
  const avgSpent = _.meanBy(userHistory, 'price');
  const priceDiff = Math.abs(product.price - avgSpent) / avgSpent;
  score += Math.max(0, 20 - (priceDiff * 20));
  
  // Rating (0-20 points)
  score += (product.rating / 5) * 20;
  
  // Popularity (0-10 points)
  score += Math.min(10, (product.purchase_count / 1000) * 10);
  
  // Recency bonus (0-10 points)
  const daysOld = (Date.now() - new Date(product.created_at)) / (1000 * 60 * 60 * 24);
  if (daysOld < 30) {
    score += 10;
  } else if (daysOld < 90) {
    score += 5;
  }
  
  return {
    ...product,
    recommendation_score: Math.round(score),
    match_reasons: []
  };
});

// Sort and take top recommendations
const recommendations = _.chain(scoredProducts)
  .orderBy(['recommendation_score', 'rating'], ['desc', 'desc'])
  .take(10)
  .value();

return {
  recommendations: recommendations,
  user_preferences: categoryPreferences,
  recommendation_count: recommendations.length
};

Example 3: Fraud Detection Scoring

const transaction = input.transaction;
const userProfile = input.user_profile;
const moment = require('moment');

let riskScore = 0;
const riskFactors = [];

// Unusual amount check (0-30 points)
const avgTransaction = userProfile.avg_transaction_amount;
const amountDeviation = Math.abs(transaction.amount - avgTransaction) / avgTransaction;
if (amountDeviation > 5) {
  riskScore += 30;
  riskFactors.push("Amount 5x higher than average");
} else if (amountDeviation > 2) {
  riskScore += 15;
  riskFactors.push("Amount 2x higher than average");
}

// Location check (0-25 points)
if (transaction.location.country !== userProfile.country) {
  riskScore += 25;
  riskFactors.push("Transaction from different country");
} else if (transaction.location.city !== userProfile.city) {
  riskScore += 10;
  riskFactors.push("Transaction from different city");
}

// Time pattern check (0-15 points)
const hour = moment(transaction.timestamp).hour();
if (hour >= 0 && hour <= 5) {
  riskScore += 15;
  riskFactors.push("Unusual time (midnight-5am)");
}

// Velocity check (0-20 points)
const recentTransactions = userProfile.transactions_last_24h || 0;
if (recentTransactions > 10) {
  riskScore += 20;
  riskFactors.push("High transaction velocity (>10 in 24h)");
} else if (recentTransactions > 5) {
  riskScore += 10;
  riskFactors.push("Elevated transaction velocity");
}

// Device fingerprint (0-10 points)
if (transaction.device_id !== userProfile.known_device_ids.some(id => id === transaction.device_id)) {
  riskScore += 10;
  riskFactors.push("Unknown device");
}

// Determine risk level
let riskLevel;
if (riskScore >= 70) {
  riskLevel = "high";
} else if (riskScore >= 40) {
  riskLevel = "medium";
} else {
  riskLevel = "low";
}

// Recommended action
let action;
if (riskLevel === "high") {
  action = "block_and_review";
} else if (riskLevel === "medium") {
  action = "require_verification";
} else {
  action = "approve";
}

return {
  risk_score: riskScore,
  risk_level: riskLevel,
  risk_factors: riskFactors,
  recommended_action: action,
  transaction_id: transaction.id,
  requires_manual_review: riskScore >= 60
};

Best Practices

Use Judiciously

Only use Eval when built-in steps (Map, Rules, Functions, Condition) can’t accomplish the task. Eval adds complexity.

Always Return a Value

Code must include a return statement. The returned value becomes the step output.

Handle Errors

Use try-catch blocks for operations that might fail. Return error information for debugging.

Keep It Fast

Optimize for performance. Long-running code slows flows. Set appropriate timeouts.

Test Thoroughly

Test with real data and edge cases. Use Test Mode to verify before production.

Document Complex Logic

Add comments explaining what the code does and why. Future you will thank present you.

Avoid External API Calls

Use HTTP Request step for API calls, not fetch/axios in Eval. Eval is for computation, not I/O.

Validate Inputs

Check that input has expected structure before processing. Return meaningful errors if not.

Troubleshooting

Code execution fails

Causes:

Syntax error in JavaScript
Runtime error (undefined variable, null reference)
Exceeded timeout
Missing return statement

Solutions:

Check execution logs for error message
Test code separately in JavaScript console
Add try-catch blocks
Verify all variables exist before using
Add return statement

Can't access input data

Causes:

Wrong variable name
Input not passed correctly
Variable undefined

Solutions:

Use input to access passed data
Use context for full flow context
Check input configuration
Add null checks: const value = input?.field || 'default'

Library not available

Causes:

Library not included in Eval environment
Wrong import syntax

Solutions:

Check available libraries list
Use correct require syntax: const _ = require('lodash')
For unavailable libraries, implement logic directly or use different step

Timeout errors

Causes:

Code takes too long to execute
Infinite loop
Processing large datasets

Solutions:

Optimize algorithm
Increase timeout setting
Process data in smaller chunks
Use Map step for large array processing instead

Unexpected output

Causes:

Logic error in code
Wrong data types
Missing edge case handling

Solutions:

Add console.log statements (appear in logs)
Test with various inputs
Verify data types match expectations
Handle null/undefined cases

Security Considerations

No External Network Access

Eval cannot make external HTTP requests. Use HTTP Request step for API calls.Blocked:

fetch()
XMLHttpRequest
axios
node-fetch

Secrets Access

Can read secrets but not write them

// Read secret
const apiKey = secrets.api_key;

// Cannot modify
// secrets.api_key = "new_value"; // ERROR

Input Validation

Always validate input data, especially user-provided data

// Validate before processing
if (!input || typeof input.amount !== 'number') {
  return {
    error: true,
    message: "Invalid input: amount must be a number"
  };
}

Sandboxed Execution

Code runs in isolated environment

Cannot access file system
Cannot execute system commands
Cannot import arbitrary modules
Timeout enforced automatically

Next Steps

Map Step

Simpler data transformations

Rules Step

Declarative business logic

Functions Step

Pre-built utility functions

Condition Step

Route based on Eval output

Get Started

Flows

Agents

Account Management

Advanced

Eval

Eval Step

How It Works

When to Use Eval

Configuration

Code

Input Data

Timeout

Available Libraries

Common Patterns

Real-World Examples

Example 1: Mortgage Qualification Calculator

Example 2: Recommendation Engine

Example 3: Fraud Detection Scoring

Best Practices

Use Judiciously

Always Return a Value

Handle Errors

Keep It Fast

Test Thoroughly

Document Complex Logic

Avoid External API Calls

Validate Inputs

Troubleshooting

Security Considerations

Next Steps

Map Step

Rules Step

Functions Step

Condition Step

Get Started

Flows

Agents

Account Management

Advanced

​Eval Step

​How It Works

​When to Use Eval

​Configuration

​Code

​Input Data

​Timeout

​Available Libraries

​Common Patterns

​Real-World Examples

​Example 1: Mortgage Qualification Calculator

​Example 2: Recommendation Engine

​Example 3: Fraud Detection Scoring

​Best Practices

Use Judiciously

Always Return a Value

Handle Errors

Keep It Fast

Test Thoroughly

Document Complex Logic

Avoid External API Calls

Validate Inputs

​Troubleshooting

​Security Considerations

​Next Steps

Map Step

Rules Step

Functions Step

Condition Step

Eval Step

How It Works

When to Use Eval

Configuration

Code

Input Data

Timeout

Available Libraries

Common Patterns

Real-World Examples

Example 1: Mortgage Qualification Calculator

Example 2: Recommendation Engine

Example 3: Fraud Detection Scoring

Best Practices

Troubleshooting

Security Considerations

Next Steps