Documenting Smart Contracts with NatSpec

This guide explains how to properly document Solidity smart contracts using NatSpec (Natural Specification) format and generate API documentation automatically.

Overview

The ATS contracts use NatSpec (Ethereum Natural Language Specification Format) for inline documentation. This documentation is automatically extracted and published to the API Documentation section.

NatSpec Basics

NatSpec uses special comment formats that are processed by documentation generators:

• /// - Single-line NatSpec comment
• /** ... */ - Multi-line NatSpec comment

NatSpec Tags

Tag	Purpose	Where to Use
@title	Contract name	Contract definition
@author	Contract author	Contract definition
@notice	User-facing description	Contract, functions, events
@dev	Developer notes	Contract, functions, modifiers
@param	Parameter description	Functions with parameters
@return	Return value description	Functions that return values
@inheritdoc	Inherit documentation	Override functions
@custom:*	Custom tags	Any context-specific info

Documentation Structure

Contract Documentation

Every contract should have a title and notice explaining its purpose:

/**
 * @title BondFacet
 * @author Hedera Hashgraph
 * @notice Manages bond-specific operations including coupon payments and maturity redemption
 * @dev Implements bond lifecycle management using Diamond storage pattern
 * @custom:security-contact security@hedera.com
 */
contract BondFacet is IBond, AccessControlStorageWrapper {
  // Contract implementation
}

Function Documentation

Document all public and external functions with clear descriptions:

/**
 * @notice Pay a coupon to all bond holders based on a snapshot
 * @dev Executes the coupon payment distribution and updates payment history
 * @param security The security token address for which to pay coupons
 * @param couponDate The date identifier for this coupon payment
 * @param paymentTokenAddress The ERC20 token used for payment
 * @param totalAmount The total amount to be distributed
 * @return success True if the payment was successfully initiated
 */
function payCoupon(
  address security,
  uint256 couponDate,
  address paymentTokenAddress,
  uint256 totalAmount
) external override returns (bool success) {
  // Implementation
}

Internal Functions

Internal functions should use @dev for implementation details:

/**
 * @dev Calculates the pro-rata coupon amount for a specific holder
 * @param holderBalance The holder's token balance at snapshot time
 * @param totalSupply The total supply at snapshot time
 * @param totalCoupon The total coupon amount to distribute
 * @return amount The calculated coupon amount for the holder
 */
function _calculateCouponAmount(
  uint256 holderBalance,
  uint256 totalSupply,
  uint256 totalCoupon
) internal pure returns (uint256 amount) {
  // Implementation
}

Events Documentation

Document all events with clear descriptions of when they're emitted:

/**
 * @notice Emitted when a coupon payment is successfully completed
 * @param security The security token address
 * @param couponDate The coupon payment date identifier
 * @param totalAmount The total amount paid
 * @param recipientCount The number of recipients who received payment
 */
event CouponPaid(address indexed security, uint256 indexed couponDate, uint256 totalAmount, uint256 recipientCount);

Modifiers Documentation

Document modifiers explaining their validation logic:

/**
 * @notice Ensures the caller has the BOND_MANAGER role
 * @dev Reverts with AccessDenied if caller lacks the required role
 */
modifier onlyBondManager() {
    require(hasRole(BOND_MANAGER_ROLE, msg.sender), "AccessDenied");
    _;
}

Storage Documentation

Document storage structures and state variables:

/**
 * @notice Bond configuration and state data
 * @dev Stored in Diamond storage pattern to support upgradeability
 * @custom:storage-location erc1967:bondFacet.storage
 */
struct BondStorage {
  /// @notice Mapping of security addresses to their bond configurations
  mapping(address => BondConfig) bondConfigs;
  /// @notice Mapping of security and coupon date to payment records
  mapping(address => mapping(uint256 => CouponPayment)) couponPayments;
  /// @notice The default payment token for coupon distributions
  address defaultPaymentToken;
}

Errors Documentation

Document custom errors with clear descriptions:

/**
 * @notice Thrown when attempting to pay a coupon for an invalid date
 * @param security The security token address
 * @param couponDate The invalid coupon date provided
 */
error InvalidCouponDate(address security, uint256 couponDate);

/**
 * @notice Thrown when insufficient funds are available for payment
 * @param required The amount required for the payment
 * @param available The amount currently available
 */
error InsufficientFunds(uint256 required, uint256 available);

Best Practices

1. Be Clear and Concise

Write documentation for developers who are unfamiliar with the code:

// ❌ Bad - too vague
/// @notice Does stuff with bonds
function processBond() external;

// ✅ Good - specific and clear
/// @notice Matures a bond and releases principal to token holders
/// @dev Transfers the bond's face value to all holders proportionally
function processBond() external;

2. Document the "Why", Not Just the "What"

// ❌ Bad - only describes what
/// @dev Sets the maturity date
function setMaturityDate(uint256 date) external;

// ✅ Good - explains why and constraints
/// @notice Sets the bond maturity date when principal becomes due
/// @dev Can only be called before the bond is issued. Once set, cannot be changed
///      to ensure investor certainty. Maturity date must be in the future.
function setMaturityDate(uint256 date) external;

3. Document Edge Cases and Constraints

/**
 * @notice Transfers tokens between accounts with compliance checks
 * @dev Validates the transfer against KYC, freeze, and partition restrictions
 * @param from The sender address (must have sufficient balance)
 * @param to The recipient address (must pass KYC and not be frozen)
 * @param amount The amount to transfer (must be > 0 and <= sender balance)
 * @return success True if transfer was successful
 *
 * Requirements:
 * - `from` must have at least `amount` tokens
 * - `to` must be KYC verified
 * - Neither `from` nor `to` can be frozen
 * - Transfer must comply with all active compliance modules
 */
function transfer(address from, address to, uint256 amount) external returns (bool success);

4. Link Related Functions

/**
 * @notice Creates a snapshot of current token holder balances
 * @dev The snapshot ID can be used in {payCoupon} to execute payments
 * @param security The security token to snapshot
 * @return snapshotId The unique identifier for this snapshot
 * @see payCoupon
 */
function createSnapshot(address security) external returns (uint256 snapshotId);

5. Document Security Considerations

/**
 * @notice Updates the bond's interest rate
 * @dev ⚠️ SECURITY: This is a privileged operation that affects all bond holders
 *      Only BOND_ADMIN role can call this function. Rate changes do not apply
 *      retroactively to already-accrued interest.
 * @param security The bond token address
 * @param newRate The new annual interest rate in basis points (e.g., 500 = 5%)
 * @custom:security Critical - requires BOND_ADMIN role
 * @custom:emits InterestRateUpdated
 */
function updateInterestRate(address security, uint256 newRate) external;

Generating Documentation

Prerequisites

Ensure you're in the contracts directory:

cd packages/ats/contracts

Generate API Documentation

Run the documentation generator:

npm run doc

This command:

1. Extracts NatSpec comments from all contracts
2. Generates markdown files in /docs/references/api/ats-contracts/
3. Organizes documentation by contract hierarchy

Configuration

The documentation generator is configured in hardhat.config.ts:

dodoc: {
  runOnCompile: false,         // Don't auto-generate on every compile
  outputDir: "../../../docs/references/api/ats-contracts",
  freshOutput: true,           // Clear old docs before generating
  include: ["contracts"],      // Include all contracts
  exclude: [
    "contracts/test",          // Exclude test contracts
    "contracts/mocks",         // Exclude mock contracts
    "node_modules"             // Exclude dependencies
  ],
},

Viewing Generated Documentation

After generation, the documentation is available at:

• Local: http://localhost:3000/docs/references/api
• Production: https://hashgraph.github.io/asset-tokenization-studio/docs/references/api

Documentation Workflow

During Development

1. Write the contract with inline NatSpec comments
2. Document as you code - don't leave it for later
3. Review your documentation before submitting PR

Before Committing

1. Generate docs to verify NatSpec is valid:

   npm run doc

2. Check for warnings - fix any NatSpec syntax errors

3. Review generated output in /docs/references/api/

In Pull Requests

• Documentation changes are automatically reviewed
• Generated API docs should be committed with code changes
• CI/CD pipeline will verify documentation builds successfully

Common Patterns in ATS

Facet Pattern Documentation

Document facets with their layer and purpose:

/**
 * @title BondFacet
 * @author Hedera Hashgraph
 * @notice Layer 2 facet implementing bond-specific corporate actions
 * @dev Part of the Diamond pattern - uses BondStorageWrapper for data access
 * @custom:layer Layer 2 - Domain Features
 * @custom:security-contact security@hedera.com
 */
contract BondFacet is IBond, BondStorageWrapper {
  // Implementation
}

Storage Wrapper Documentation

Document storage access patterns:

/**
 * @title BondStorageWrapper
 * @notice Provides type-safe access to bond storage in Diamond pattern
 * @dev Implements the storage access layer for bond data
 * @custom:layer Layer 0 - Storage
 */
abstract contract BondStorageWrapper {
  /**
   * @dev Returns the bond storage pointer
   * @return s Storage pointer to BondStorage struct
   * @custom:storage-location erc1967:bondFacet.storage
   */
  function _bondStorage() internal pure returns (BondStorage storage s);
}

Interface Documentation

Document interfaces with implementation requirements:

/**
 * @title IBond
 * @notice Interface for bond token operations
 * @dev Implementers must support coupon payments and maturity redemption
 */
interface IBond {
  /**
   * @notice Pay a coupon to bond holders
   * @dev Must validate caller permissions and check payment token allowance
   * @param security The bond token address
   * @param amount The total coupon amount
   * @return success True if payment initiated successfully
   */
  function payCoupon(address security, uint256 amount) external returns (bool success);
}

Troubleshooting

Common Issues

Issue: Documentation generator fails

Error: Unable to find contract sources

Solution: Ensure contracts are compiled first:

npm run compile
npm run doc

---

Issue: Missing documentation in generated output

Solution: Check that your NatSpec uses proper syntax:

• Use /// or /** */ format
• Place comments directly above the documented element
• Include required tags (@notice for public functions)

---

Issue: Documentation not showing in Docusaurus

Solution: Rebuild the documentation site:

cd ../../../apps/docs
npm run build

Additional Resources

• NatSpec Format Specification
• Solidity Documentation Best Practices
• Hardhat Dodoc Plugin Documentation

Summary

• ✅ Use NatSpec format for all public interfaces
• ✅ Document functions with @notice, @dev, @param, @return
• ✅ Include security considerations and constraints
• ✅ Generate docs with npm run doc before committing
• ✅ Review generated documentation for clarity

Well-documented contracts make the codebase more maintainable and help developers understand the system architecture and business logic.