# Understanding the cheqd SDK

This guide provides a clear understanding of the cheqd SDK's architecture, modules, and practical use cases to help you choose the right tools for your decentralized identity solutions.

## SDK Architecture Overview

The cheqd SDK is built around four core modules that work together to provide comprehensive identity management and transaction processing capabilities:

{% @mermaid/diagram content="graph TB
A\[cheqd SDK] --> B\[DID Module]
A --> C\[Resource Module]
A --> D\[Fee Abstraction Module]
A --> E\[Feemarket Module]

```
B --> F[Identity Operations]
C --> G[Linked Resources]
D --> H[Multi-Token Fees]
E --> I[Dynamic Pricing]" %}
```

## Module Overview & Use Cases

### 🆔 DID Module

**Purpose**: Complete lifecycle management for Decentralized Identifiers

**Key Features**:

* Create, update, and deactivate DIDs
* Support for multiple verification methods (Ed25519, secp256k1, RSA)
* Key rotation and authentication management
* Integration with fee abstraction and dynamic pricing

**When to Use**:

* Building identity wallets or credential platforms
* Creating enterprise identity systems
* Developing SSI (Self-Sovereign Identity) applications
* Managing organizational identities

**Practical Use Cases**:

* **Digital Identity Wallets**: Create DIDs for users with multiple authentication methods → [See DID Creation Guide](/product/advanced/sdk/did-module/create-did.md)
* **Enterprise Identity**: Manage corporate identities with key rotation capabilities → [See DID Management](https://github.com/cheqd/identity-docs/blob/main/advanced/sdk/did-module/manage-did.md)
* **Multi-Signature Operations**: Set up DIDs with multiple controllers for organizational use → [See Multi-Controller Setup](/product/advanced/sdk/did-module.md#multi-controller-operations)

### 📁 Resource Module

**Purpose**: Create and manage DID-Linked Resources (schemas, credential definitions, revocation lists)

**Key Features**:

* Store schemas, credential definitions, and revocation registries
* Version control and resource linking
* Flexible media type support (JSON, images, documents)
* Resource collection management

**When to Use**:

* Building credential issuance platforms
* Creating verifiable credential ecosystems
* Managing schema registries
* Storing credential-related metadata

**Practical Use Cases**:

* **Credential Schema Management**: Store and version credential schemas for issuers → [See Resource Creation](/product/advanced/sdk/resource-module.md#credential-schemas)
* **Revocation Lists**: Manage credential revocation registries → [See Status Lists](/product/advanced/sdk/resource-module.md#status-lists)
* **Trust Registry Data**: Store trusted issuer lists and governance documents → [See Trust Registries](/product/advanced/sdk/resource-module.md#trust-registries)

### 💱 Fee Abstraction Module

**Purpose**: Pay transaction fees using alternative IBC tokens instead of native CHEQ

**Key Features**:

* Support for USDC, EURe, OSMO, and other IBC tokens
* Automatic rate conversion and fee calculation
* Cross-chain fee payment capabilities
* Integration with all identity operations

**When to Use**:

* Applications requiring stable fee costs
* Cross-chain identity solutions
* Enterprise applications with specific token preferences
* Users wanting to avoid native token volatility

**Practical Use Cases**:

* **Stablecoin Fee Strategy**: Pay fees in USDC for predictable costs → [See USDC Integration](/product/advanced/sdk/fee-abstraction/using-in-transactions.md#usdc-payments)
* **Cross-Chain Applications**: Accept fees in tokens from connected Cosmos chains → [See IBC Token Usage](/product/advanced/sdk/fee-abstraction.md#supported-tokens)
* **Enterprise Fee Management**: Use EUR-backed tokens for regulatory compliance → [See EURe Integration](/product/advanced/sdk/fee-abstraction/using-in-transactions.md#eure-payments)

### 📈 Feemarket Module

**Purpose**: Dynamic fee calculation based on network congestion for Cosmos SDK transactions

**Key Features**:

* Real-time gas price adjustment
* Network congestion-based pricing
* Automatic fee optimization
* Standard Cosmos SDK transaction support

**When to Use**:

* Applications requiring cost optimization
* High-throughput transaction processing
* Standard Cosmos SDK operations (transfers, staking)
* Network efficiency optimization

**Practical Use Cases**:

* **Cost Optimization**: Automatically adjust fees based on network conditions → [See Dynamic Pricing](/product/advanced/sdk/dynamic-fees.md)
* **High-Volume Operations**: Process many transactions efficiently → [See Fee Optimization](https://github.com/cheqd/identity-docs/blob/main/advanced/sdk/feemarket-module/README.md#optimization-strategies)
* **Network Management**: Monitor and respond to congestion → [See Real-Time Pricing](https://github.com/cheqd/identity-docs/blob/main/advanced/sdk/feemarket-module/README.md#dynamic-pricing)

## Integration Patterns

### Module Combinations for Common Scenarios

#### 🏢 Enterprise Identity Platform

**Modules**: DID + Resource + Fee Abstraction **Use Case**: Corporate identity management with stable costs

```typescript
// Create enterprise DID with USDC fees
const enterpriseDID = await didModule.createDidDocTx(signInputs, payload, feePayer, usdcFee);

// Store governance documents as resources
const governanceDoc = await resourceModule.createLinkedResourceTx(resourceInputs, payload, feePayer, usdcFee);
```

#### 🎓 Educational Credential System

**Modules**: DID + Resource + Fee Abstraction\
**Use Case**: University credential issuance with predictable fee costs

```typescript
// Create institution DID
const universityDID = await didModule.createDidDocTx(/* institution setup */);

// Create credential schema as resource
const degreeSchema = await resourceModule.createLinkedResourceTx(/* schema setup */);
```

#### 💳 High-Volume Transaction Processing

**Modules**: DID + Feemarket **Use Case**: Efficient transaction processing with dynamic pricing

```typescript
// Get optimal gas price from feemarket
const gasPrice = await feemarketModule.getGasPrice();

// Process transactions with optimized fees
const result = await signer.signAndBroadcast(address, messages, gasPrice);
```

#### 🌐 Cross-Chain Identity Bridge

**Modules**: All Modules **Use Case**: Multi-chain identity with flexible fee payment

```typescript
// Support both fee abstraction and dynamic pricing
const feeStrategy = networkCongestion > threshold ? 
  await feemarketModule.calculateOptimalFee() : 
  await feeAbstractionModule.convertToPreferredToken(baseFee);
```

## Advanced Capabilities

### 🔧 Gas Simulation & Transaction Optimization

For production applications requiring precise cost control and reliable execution:

**Key Features**:

* Pre-transaction gas estimation
* Smart transaction batching
* Built-in retry mechanisms with exponential backoff
* Circuit breaker patterns for resilience

**When to Use**:

* Production applications with SLA requirements
* High-value transactions requiring certainty
* Batch processing operations
* Cost-sensitive applications

**Learn More**: [Gas Simulation & Optimization Guide](/product/advanced/sdk/simulation-gas-optimization.md)

## Quick Decision Matrix

Use this matrix to quickly identify which modules you need:

| Your Requirement              | Recommended Modules              | Key Use Cases                        |
| ----------------------------- | -------------------------------- | ------------------------------------ |
| **Basic Identity Management** | DID Module                       | User accounts, authentication        |
| **Credential Issuance**       | DID + Resource                   | Schemas, credential definitions      |
| **Stable Fee Costs**          | Any Module + Fee Abstraction     | Enterprise apps, predictable budgets |
| **Cost Optimization**         | Any Module + Feemarket           | High-volume apps, efficiency focus   |
| **Cross-Chain Identity**      | DID + Resource + Fee Abstraction | Multi-chain applications             |
| **Production Reliability**    | All Modules + Gas Simulation     | Mission-critical applications        |

## Getting Started

1. **Start Here**: [SDK Setup Guide](https://github.com/cheqd/identity-docs/blob/main/advanced/sdk/sdk-setup.md) - Install and configure the SDK
2. **Choose Your Path**:
   * **Identity First**: Begin with [DID Module](/product/advanced/sdk/did-module.md)
   * **Cost Control**: Start with [Fee Abstraction](/product/advanced/sdk/fee-abstraction.md)
   * **Optimization**: Explore [Gas Simulation](/product/advanced/sdk/simulation-gas-optimization.md)
3. **Advanced Integration**: Combine modules based on your specific requirements

## Module Documentation

* [**DID Module**](/product/advanced/sdk/did-module.md) - Complete DID lifecycle management
* [**Resource Module**](/product/advanced/sdk/resource-module.md) - DID-Linked Resource operations
* [**Fee Abstraction Module**](/product/advanced/sdk/fee-abstraction.md) - Multi-token fee payments
* [**Feemarket Module**](https://github.com/cheqd/identity-docs/blob/main/advanced/sdk/feemarket-module/README.md) - Dynamic fee optimization
* [**Gas Simulation Guide**](/product/advanced/sdk/simulation-gas-optimization.md) - Advanced transaction optimization

Each module includes comprehensive examples, error handling patterns, and production best practices to help you build robust decentralized identity solutions.


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