diff --git a/server/src/main/kotlin/org/ccoin/models/ApiResponse.kt b/server/src/main/kotlin/org/ccoin/models/ApiResponse.kt
index e69de29..b154d61 100644
--- a/server/src/main/kotlin/org/ccoin/models/ApiResponse.kt
+++ b/server/src/main/kotlin/org/ccoin/models/ApiResponse.kt
@@ -0,0 +1,80 @@
+package org.ccoin.models
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ApiResponse<T>(
+    val success: Boolean,
+    val data: T? = null,
+    val error: String? = null,
+    val timestamp: Long = System.currentTimeMillis()
+)
+
+@Serializable
+data class ErrorResponse(
+    val error: String,
+    val code: String? = null,
+    val details: Map<String, String>? = null,
+    val timestamp: Long = System.currentTimeMillis()
+)
+
+@Serializable
+data class SuccessResponse(
+    val message: String,
+    val timestamp: Long = System.currentTimeMillis()
+)
+
+@Serializable
+data class HealthResponse(
+    val status: String,
+    val version: String,
+    val uptime: Long,
+    val database: DatabaseHealth,
+    val blockchain: BlockchainHealth
+)
+
+@Serializable
+data class DatabaseHealth(
+    val connected: Boolean,
+    val responseTime: Long,
+    val activeConnections: Int,
+    val maxConnections: Int
+)
+
+@Serializable
+data class BlockchainHealth(
+    val latestBlock: Int,
+    val pendingTransactions: Int,
+    val networkHashRate: Double,
+    val averageBlockTime: Long
+)
+
+@Serializable
+data class PaginationRequest(
+    val page: Int = 1,
+    val pageSize: Int = 50,
+    val sortBy: String? = null,
+    val sortOrder: SortOrder = SortOrder.DESC
+)
+
+@Serializable
+data class PaginatedResponse<T>(
+    val data: List<T>,
+    val pagination: PaginationInfo
+)
+
+@Serializable
+data class PaginationInfo(
+    val currentPage: Int,
+    val pageSize: Int,
+    val totalItems: Int,
+    val totalPages: Int,
+    val hasNext: Boolean,
+    val hasPrevious: Boolean
+)
+
+@Serializable
+enum class SortOrder {
+    ASC,
+    DESC
+}
diff --git a/server/src/main/kotlin/org/ccoin/models/Block.kt b/server/src/main/kotlin/org/ccoin/models/Block.kt
index e69de29..a1b8966 100644
--- a/server/src/main/kotlin/org/ccoin/models/Block.kt
+++ b/server/src/main/kotlin/org/ccoin/models/Block.kt
@@ -0,0 +1,53 @@
+package org.ccoin.models
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class StartMiningRequest(
+    val minerAddress: String, // Format: random_word:random_6_digits
+    val difficulty: Int? = null
+)
+
+@Serializable
+data class SubmitMiningRequest(
+    val minerAddress: String,
+    val nonce: Long,
+    val hash: String,
+    val previousHash: String,
+    val timestamp: Long
+)
+
+@Serializable
+data class BlockResponse(
+    val hash: String,
+    val previousHash: String?,
+    val merkleRoot: String,
+    val timestamp: Long,
+    val difficulty: Int,
+    val nonce: Long,
+    val minerAddress: String
+    val reward: Double,
+    val height: Int,
+    val transactionCount: Int,
+    val confirmations: Int = 0
+)
+
+@Serializable
+data class MiningJobResponse(
+   val jobId: String,
+   val target: String,
+   val difficulty: Int,
+   val previousHash: String,
+   val height: Int,
+   val timestamp: Long,
+   val expiresAt: Long
+)
+
+@Serializable
+data class MiningStatsResponse(
+    val minerAddress: String,
+    val totalBlocksMined: Int,
+    val totalRewardEarned: Double,
+    val lastBlockMined: Long?,
+    val currentDifficulty: Int
+)
diff --git a/server/src/main/kotlin/org/ccoin/models/Transaction.kt b/server/src/main/kotlin/org/ccoin/models/Transaction.kt
index e69de29..a2d84a7 100644
--- a/server/src/main/kotlin/org/ccoin/models/Transaction.kt
+++ b/server/src/main/kotlin/org/ccoin/models/Transaction.kt
@@ -0,0 +1,42 @@
+package org.ccoin.models
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class SendTransactionRequest(
+    val fromAddress: String, // Format random_word:random_6_digits
+    val toAddress: String, // Format random_word:random_6_digits
+    val amount: Double,
+    val fee: Double = 0.0,
+    val memo: String? = null
+)
+
+@Serializable
+data class TransactionResponse(
+    val hash: String,
+    val fromAddress: String?,
+    val toAddress: String,
+    val amount: Double,
+    val fee: Double,
+    val memo: String?,
+    val blockHash: String?,
+    val timestamp: Long,
+    val status: TransactionStatus,
+    val confirmations: Int = 0
+)
+
+@Serializable
+data class TransactionHistoryResponse(
+    val transactions: List<TransactionResponse>,
+    val totalCount: Int,
+    val page: Int,
+    val pageSize: Int
+)
+
+@Serializable
+enum class TransactionStatus {
+    PENDING,
+    CONFIRMED,
+    FAILED,
+    CANCELLED
+}
diff --git a/server/src/main/kotlin/org/ccoin/models/Wallet.kt b/server/src/main/kotlin/org/ccoin/models/Wallet.kt
index e69de29..cae2ec2 100644
--- a/server/src/main/kotlin/org/ccoin/models/Wallet.kt
+++ b/server/src/main/kotlin/org/ccoin/models/Wallet.kt
@@ -0,0 +1,28 @@
+package org.ccoin.models
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class CreateWalletRequest(
+    val label: String? = null
+)
+
+@Serializable
+data class WalletResponse(
+    val address: String, // Format random_word:random_6_digits (e.g. "phoenix:123456")
+    val balance: Double,
+    val label: String?,
+    val createdAt: Long,
+    val lastActivity: Long?
+)
+
+@Serializable
+data class BalanceResponse(
+    val address: String,
+    val balance: Double
+)
+
+@Serializable
+data class UpdateWalletRequest(
+    val label: String?
+)