> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cosmos.network/llms.txt
> Use this file to discover all available pages before exploring further.

# Feemarket

> EIP-1559 modualarized

The feemarket module from [cosmos/evm](https://github.com/cosmos/evm) implements [EIP-1559](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1559.md) dynamic fee pricing for Cosmos SDK chains with EVM compatibility.

<Note>
  This is part of cosmos/evm, not standard Cosmos SDK. For conceptual understanding of EIP-1559, see [EIP-1559 Fee Market](/evm/v0.4.x/documentation/concepts/eip-1559-feemarket).
</Note>

## Parameters

The module contains the following parameters ([types](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/types/params.go), [proto](https://github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/feemarket.proto)):

| Parameter                  | Type    | Default      | Description                                                   |
| -------------------------- | ------- | ------------ | ------------------------------------------------------------- |
| `NoBaseFee`                | bool    | `false`      | Disables EIP-1559 base fee (enables legacy pricing)           |
| `BaseFeeChangeDenominator` | uint32  | `8`          | Controls max base fee change per block (higher = more stable) |
| `ElasticityMultiplier`     | uint32  | `2`          | Determines target block utilization (2 = 50% target)          |
| `EnableHeight`             | int64   | `0`          | Block height to activate fee market (0 = genesis)             |
| `BaseFee`                  | sdk.Dec | `1000000000` | Current base fee (auto-adjusts each block)                    |
| `MinGasPrice`              | sdk.Dec | `0`          | Minimum gas price floor (cannot go below)                     |
| `MinGasMultiplier`         | sdk.Dec | `0.5`        | Minimum gas used multiplier for gas wanted                    |

### Parameter Details

<Expandable title="BaseFeeChangeDenominator">
  Controls fee volatility by limiting the maximum change per block:

  | Value | Max Change/Block | Blocks to 10x | Use Case                        |
  | ----- | ---------------- | ------------- | ------------------------------- |
  | 4     | ±25%             | \~10 blocks   | Testnets, rapid price discovery |
  | **8** | ±12.5%           | \~20 blocks   | Ethereum standard, balanced     |
  | 16    | ±6.25%           | \~40 blocks   | Stable fees, production chains  |
  | 32    | ±3.125%          | \~80 blocks   | Very stable, enterprise chains  |
</Expandable>

<Expandable title="ElasticityMultiplier">
  Sets the target block utilization:

  | Value | Target % | Behavior                      | Recommended For               |
  | ----- | -------- | ----------------------------- | ----------------------------- |
  | 1     | 100%     | Only increases at full blocks | Maximum throughput chains     |
  | **2** | 50%      | Balanced (Ethereum standard)  | General purpose chains        |
  | 4     | 25%      | Aggressive fee increases      | Anti-spam focused chains      |
  | 10    | 10%      | Very aggressive pricing       | High-value transaction chains |
</Expandable>

<Expandable title="MinGasPrice">
  Sets the absolute price floor:

  ```
  BaseFee = max(CalculatedBaseFee, MinGasPrice)
  ```

  This prevents fees from dropping too low during periods of low activity, maintaining spam resistance.
</Expandable>

### Parameter Storage Format

`sdk.Dec` (LegacyDec) values are stored as strings with 18 decimal precision ([cosmos-sdk](https://github.com/cosmos/cosmos-sdk/blob/main/math/dec.go)):

| Human Value | Stored String                  | Formula      |
| ----------- | ------------------------------ | ------------ |
| 1 unit      | "1000000000000000000"          | 1 × 10^18    |
| 0.5 (50%)   | "500000000000000000"           | 0.5 × 10^18  |
| 1 billion   | "1000000000000000000000000000" | 10^9 × 10^18 |

## Configuration

Adjust parameters to achieve specific network behaviors ([params validation](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/types/params.go#L43-L142)):

| **Goal**                | **Parameter**                 | **Adjustment** | **Effect**                               |
| ----------------------- | ----------------------------- | -------------- | ---------------------------------------- |
| Faster fee response     | `base_fee_change_denominator` | 8 → 4          | 2x faster adjustments (±25% vs ±12.5%)   |
| More stable fees        | `base_fee_change_denominator` | 8 → 16         | 2x slower adjustments (±6.25% vs ±12.5%) |
| Earlier fee increases   | `elasticity_multiplier`       | 2 → 4          | Fees rise at 25% vs 50% utilization      |
| Stronger spam deterrent | `min_gas_price`               | Low → High     | Higher transaction cost floor            |

### Configuration Profiles

<CodeGroup>
  ```json Ethereum-Compatible theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  {
    "no_base_fee": false,
    "base_fee_change_denominator": 8,      // ±12.5% max per block
    "elasticity_multiplier": 2,            // 50% target utilization
    "enable_height": 0,                    // Active from genesis
    "base_fee": "1000000000000000000000",  // Starting base fee
    "min_gas_price": "1000000000000000000", // Price floor
    "min_gas_multiplier": "500000000000000000" // 0.5 (anti-manipulation)
  }
  // Behavior: Standard Ethereum, balanced for general use
  // 100k gas tx: ~0.1 tokens at base, up to 10x during congestion
  ```

  ```json High-Volume-Stable theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  {
    "no_base_fee": false,
    "base_fee_change_denominator": 16,     // ±6.25% max per block
    "elasticity_multiplier": 2,            // 50% target utilization
    "enable_height": 0,
    "base_fee": "100000000000000000000",   // Lower starting fee
    "min_gas_price": "10000000000000000",  // Lower floor
    "min_gas_multiplier": "500000000000000000"
  }
  // Behavior: Slow, predictable changes for DeFi/DEX chains
  // 100k gas tx: ~0.01 tokens, gradual increases
  ```

  ```json Aggressive-Anti-Spam theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  {
    "no_base_fee": false,
    "base_fee_change_denominator": 4,      // ±25% max per block
    "elasticity_multiplier": 4,            // 25% target utilization
    "enable_height": 0,
    "base_fee": "10000000000000000000000",  // High starting fee
    "min_gas_price": "10000000000000000000000", // High floor
    "min_gas_multiplier": "1000000000000000000" // 1.0 (strict)
  }
  // Behavior: Rapid adjustments, high minimum for premium chains
  // 100k gas tx: ~1 token minimum, aggressive scaling
  ```
</CodeGroup>

### Scenario Comparisons

<Tabs>
  <Tab title="80% Utilization (Congestion)">
    | Config                    | 5 Blocks | 10 Blocks | 10x Time    |
    | ------------------------- | -------- | --------- | ----------- |
    | **Ethereum** (d=8, e=2)   | +34%     | +79%      | \~20 blocks |
    | **Stable** (d=16, e=2)    | +16%     | +34%      | \~40 blocks |
    | **Aggressive** (d=4, e=4) | +101%    | +304%     | \~8 blocks  |
  </Tab>

  <Tab title="20% Utilization (Recovery)">
    | Config         | 5 Blocks | 10 Blocks | Floor       |
    | -------------- | -------- | --------- | ----------- |
    | **Ethereum**   | -26%     | -45%      | \~15 blocks |
    | **Stable**     | -14%     | -26%      | \~30 blocks |
    | **Aggressive** | -61%     | -85%      | \~6 blocks  |
  </Tab>
</Tabs>

### Decimal Precision Support

The module supports different token decimal configurations:

| Decimals | Conversion Factor | Min Unit Gas | Example       |
| -------- | ----------------- | ------------ | ------------- |
| 6        | 10^12             | 10^-12       | USDC          |
| 8        | 10^10             | 10^-10       | BTC-wrapped   |
| 18       | 1                 | 1            | ETH, most EVM |

## Configuration In Production

Parameters can be updated through governance proposals ([msg server](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/msg_server.go)):

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
// MsgUpdateParams structure
// Source: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/tx.proto
{
  "@type": "/cosmos.evm.feemarket.v1.MsgUpdateParams",
  "authority": "cosmos10d07y265gmmuvt4z0w9aw880jnsr700j6zn9kn",
  "params": {
    "no_base_fee": false,
    "base_fee_change_denominator": 16,
    "elasticity_multiplier": 2,
    "enable_height": 100000,
    "base_fee": "1000000000000000000000",
    "min_gas_price": "1000000000000000000",
    "min_gas_multiplier": "500000000000000000"
  }
}
```

Submit with:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Submit governance proposal
# Source: github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/msg_server.go#L17-L39
evmd tx gov submit-proposal update-feemarket-params.json \
  --from <key> \
  --deposit 1000000000stake
```

## Best Practices

### Parameter Selection by Use Case

| **Chain Type**         | **Denominator** | **Elasticity** | **MinGasPrice** | **Why**                                |
| ---------------------- | --------------- | -------------- | --------------- | -------------------------------------- |
| Testing/Development    | 8               | 2              | Zero/Low        | Quick iteration                        |
| Production General     | 8-16            | 2              | Medium          | Balance stability and responsiveness   |
| High-Frequency Trading | 16-32           | 1-2            | Low             | Predictable fees, high throughput      |
| Enterprise/Private     | 32              | 2-3            | High            | Maximum stability, cost predictability |
| Gaming/Micro-tx        | 4-8             | 1              | Very Low        | Fast adjustments, minimal fees         |

### Block Time Correlation

Faster blocks require higher denominators to maintain stability:

```
Recommended Denominator = 8 × (6s / YourBlockTime)
```

Examples:

* 1s blocks → denominator ≥16 (prevents wild swings)
* 6s blocks → denominator = 8 (Ethereum standard)
* 12s blocks → denominator = 4 (can be more responsive)

### Monitoring Key Metrics

| **Metric**       | **Formula**                  | **Healthy** | **Action if Unhealthy** |
| ---------------- | ---------------------------- | ----------- | ----------------------- |
| Fee Volatility   | `σ(fees)/μ(fees)`            | \<20% daily | Increase denominator    |
| Utilization Rate | `gasUsed/maxGas`             | 40-60% avg  | Adjust elasticity       |
| Floor Hit Rate   | `count(fee==min)\/blocks`    | \<10%       | Lower min\_gas\_price   |
| Recovery Speed   | Blocks to return to baseline | 20-40       | Tune denominator        |

### Integration Examples

<CodeGroup>
  ```javascript Wallet-Integration theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Get current base fee from latest block
  const block = await provider.getBlock('latest');
  const baseFee = block.baseFeePerGas;

  // Add buffer for inclusion certainty (20% buffer)
  const maxFeePerGas = baseFee * 120n / 100n;
  const maxPriorityFeePerGas = ethers.parseUnits("2", "gwei");

  // Send EIP-1559 transaction
  const tx = await wallet.sendTransaction({
    type: 2,
    maxFeePerGas,
    maxPriorityFeePerGas,
    to: "0x...",
    value: ethers.parseEther("1.0"),
    gasLimit: 21000
  });
  ```

  ```javascript Fee-Monitoring theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Get current gas price (includes base fee)
  const gasPrice = await provider.send('eth_gasPrice', []);
  console.log('Current gas price:', ethers.formatUnits(gasPrice, 'gwei'), 'gwei');

  // Get fee history
  const feeHistory = await provider.send('eth_feeHistory', [
    '0x10', // last 16 blocks
    'latest',
    [25, 50, 75]
  ]);

  // Process base fees from history
  const baseFees = feeHistory.baseFeePerGas.map(fee =>
    ethers.formatUnits(fee, 'gwei')
  );
  console.log('Base fee history:', baseFees);

  // Check if fees are elevated
  const currentBaseFee = BigInt(feeHistory.baseFeePerGas[feeHistory.baseFeePerGas.length - 1]);
  const threshold = ethers.parseUnits('100', 'gwei');
  const isHighFee = currentBaseFee > threshold;
  ```
</CodeGroup>

## Interfaces

### EVM JSON-RPC

The fee market integrates with standard Ethereum JSON-RPC methods ([RPC backend](https://github.com/cosmos/evm/blob/v0.4.1/rpc/backend/chain_info.go)):

<ResponseField name="eth_gasPrice" type="string">
  Returns the current base fee as hex string. In EIP-1559 mode, returns the base fee; in legacy mode, returns the median gas price.

  ```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Request
  {"jsonrpc":"2.0","method":"eth_gasPrice","params":[],"id":1}

  // Response
  {"jsonrpc":"2.0","id":1,"result":"0x3b9aca00"} // 1 gwei in hex
  ```
</ResponseField>

<ResponseField name="eth_maxPriorityFeePerGas" type="string">
  Returns suggested priority fee (tip) per gas. In cosmos/evm with the experimental mempool, transactions are prioritized by effective gas tip (fees), with ties broken by arrival time.

  ```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Request
  {"jsonrpc":"2.0","method":"eth_maxPriorityFeePerGas","params":[],"id":1}

  // Response
  {"jsonrpc":"2.0","id":1,"result":"0x77359400"} // Suggested tip in wei
  ```
</ResponseField>

<ResponseField name="eth_feeHistory" type="object">
  Returns base fee and gas utilization history for a range of blocks.

  <Expandable title="parameters">
    <ParamField body="blockCount" type="number" required>
      Number of blocks to return (hex or decimal)
    </ParamField>

    <ParamField body="newestBlock" type="string" required>
      Latest block to include ("latest", "pending", or block number)
    </ParamField>

    <ParamField body="rewardPercentiles" type="array">
      Array of percentiles for priority fee calculations
    </ParamField>
  </Expandable>

  ```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Request
  {
    "jsonrpc":"2.0",
    "method":"eth_feeHistory",
    "params":["0x5", "latest", [25, 50, 75]],
    "id":1
  }

  // Response
  {
    "jsonrpc":"2.0",
    "id":1,
    "result":{
      "baseFeePerGas": [
        "0x3b9aca00",
        "0x3c9aca00",
        "0x3d9aca00",
        "0x3e9aca00",
        "0x3f9aca00"
      ],
      "gasUsedRatio": [0.5, 0.55, 0.6, 0.48, 0.52],
      "oldestBlock": "0x1234",
      "reward": [
        ["0x0", "0x0", "0x0"],
        ["0x0", "0x0", "0x0"],
        ["0x0", "0x0", "0x0"],
        ["0x0", "0x0", "0x0"],
        ["0x0", "0x0", "0x0"]
      ]
    }
  }
  ```
</ResponseField>

<ResponseField name="eth_getBlockByNumber" type="object">
  Block responses include `baseFeePerGas` field when EIP-1559 is enabled.

  ```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  {
    "jsonrpc":"2.0",
    "id":1,
    "result":{
      "number": "0x1234",
      "hash": "0x...",
      "baseFeePerGas": "0x3b9aca00", // Base fee for this block
      // ... other block fields
    }
  }
  ```
</ResponseField>

#### Transaction Types

The fee market supports both legacy and EIP-1559 transaction types ([types](https://github.com/cosmos/evm/blob/v0.4.1/x/vm/types/tx.go)):

<CodeGroup>
  ```json Legacy-Transaction theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  {
    "type": "0x0",
    "gasPrice": "0x3b9aca00",  // Must be >= current base fee
    "gas": "0x5208",
    "to": "0x...",
    "value": "0x...",
    "data": "0x..."
  }
  ```

  ```json EIP-1559-Transaction theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  {
    "type": "0x2",
    "maxFeePerGas": "0x3b9aca00",      // Maximum total fee willing to pay
    "maxPriorityFeePerGas": "0x77359400", // Tip that affects transaction priority in mempool
    "gas": "0x5208",
    "to": "0x...",
    "value": "0x...",
    "data": "0x..."
  }
  ```
</CodeGroup>

### CLI

<CodeGroup>
  ```bash Query-Parameters theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  # Query module parameters
  # Source: github.com/cosmos/evm/blob/v0.4.1/x/feemarket/client/cli/query.go
  evmd query feemarket params
  ```

  ```bash Query-Base-Fee theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  # Query current base fee
  # Source: github.com/cosmos/evm/blob/v0.4.1/x/feemarket/client/cli/query.go
  evmd query feemarket base-fee
  ```

  ```bash Query-Block-Gas theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  # Query block gas wanted
  # Source: github.com/cosmos/evm/blob/v0.4.1/x/feemarket/client/cli/query.go
  evmd query feemarket block-gas
  ```
</CodeGroup>

### gRPC

<CodeGroup>
  ```proto Query-Parameters theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Request all module parameters
  // Proto: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/query.proto
  grpcurl -plaintext localhost:9090 feemarket.Query/Params

  // Response
  {
    "params": {
      "no_base_fee": false,
      "base_fee_change_denominator": 8,
      "elasticity_multiplier": 2,
      "enable_height": 0,
      "base_fee": "1000000000000000000000",
      "min_gas_price": "1000000000000000000",
      "min_gas_multiplier": "500000000000000000"
    }
  }
  ```

  ```proto Query-Base-Fee theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Request current base fee
  // Proto: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/query.proto
  grpcurl -plaintext localhost:9090 feemarket.Query/BaseFee

  // Response
  {
    "base_fee": "1000000000000000000000"
  }
  ```

  ```proto Query-Block-Gas theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // Request block gas wanted
  // Proto: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/query.proto
  grpcurl -plaintext localhost:9090 feemarket.Query/BlockGas

  // Response
  {
    "gas": "5000000"
  }
  ```
</CodeGroup>

### REST

<CodeGroup>
  ```http Query-Parameters theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  # REST endpoint for parameters
  # Proto: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/query.proto
  GET /cosmos/feemarket/v1/params

  // Response
  {
    "params": {
      "no_base_fee": false,
      "base_fee_change_denominator": 8,
      "elasticity_multiplier": 2,
      "enable_height": 0,
      "base_fee": "1000000000000000000000",
      "min_gas_price": "1000000000000000000",
      "min_gas_multiplier": "500000000000000000"
    }
  }
  ```

  ```http Query-Base-Fee theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  # REST endpoint for base fee
  # Proto: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/query.proto
  GET /cosmos/feemarket/v1/base_fee

  // Response
  {
    "base_fee": "1000000000000000000000"
  }
  ```

  ```http Query-Block-Gas theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  # REST endpoint for block gas
  # Proto: github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/query.proto
  GET /cosmos/feemarket/v1/block_gas

  // Response
  {
    "gas": "5000000"
  }
  ```
</CodeGroup>

## Technical Implementation

### State

The module maintains the following state ([genesis proto](https://github.com/cosmos/evm/blob/v0.4.1/proto/cosmos/evm/feemarket/v1/genesis.proto)):

#### State Objects

| State Object   | Description                     | Key              | Value            | Store     |
| -------------- | ------------------------------- | ---------------- | ---------------- | --------- |
| BlockGasWanted | Gas wanted in the current block | `[]byte{1}`      | `[]byte{uint64}` | Transient |
| BaseFee        | Current base fee                | `Params.BaseFee` | `sdk.Dec`        | KV        |
| Params         | Module parameters               | `[]byte{0x00}`   | `Params`         | KV        |

#### Genesis State

```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
type GenesisState struct {
    Params Params
    BaseFee sdk.Dec
}
```

### Begin Block

At the beginning of each block, the module calculates and sets the new base fee ([source](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/abci.go#L16-L45)):

```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
func (k Keeper) BeginBlock(ctx sdk.Context) error {
    baseFee := k.CalculateBaseFee(ctx)

    // Skip if base fee is nil (not enabled)
    if baseFee.IsNil() {
        return nil
    }

    // Update the base fee in state
    k.SetBaseFee(ctx, baseFee)

    // Emit event with new base fee
    ctx.EventManager().EmitEvent(
        sdk.NewEvent(
            "fee_market",
            sdk.NewAttribute("base_fee", baseFee.String()),
        ),
    )
    return nil
}
```

### End Block

At the end of each block, the module updates the gas wanted for base fee calculation ([source](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/abci.go#L47-L92)):

```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
func (k Keeper) EndBlock(ctx sdk.Context) error {
    gasWanted := k.GetTransientGasWanted(ctx)
    gasUsed := ctx.BlockGasMeter().GasConsumedToLimit()

    // Apply MinGasMultiplier to prevent manipulation
    // gasWanted = max(gasWanted * MinGasMultiplier, gasUsed)
    minGasMultiplier := k.GetParams(ctx).MinGasMultiplier
    limitedGasWanted := NewDec(gasWanted).Mul(minGasMultiplier)
    updatedGasWanted := MaxDec(limitedGasWanted, NewDec(gasUsed)).TruncateInt()

    // Store for next block's base fee calculation
    k.SetBlockGasWanted(ctx, updatedGasWanted)

    ctx.EventManager().EmitEvent(
        sdk.NewEvent(
            "block_gas",
            sdk.NewAttribute("height", fmt.Sprintf("%d", ctx.BlockHeight())),
            sdk.NewAttribute("amount", fmt.Sprintf("%d", updatedGasWanted)),
        ),
    )
    return nil
}
```

### Base Fee Calculation Algorithm

The calculation follows the EIP-1559 specification with Cosmos SDK adaptations ([source](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/eip1559.go#L18-L69), [utils](https://github.com/cosmos/evm/blob/v0.4.1/utils/utils.go#L229-L254)):

<Expandable title="View calculation implementation">
  ```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  func CalcGasBaseFee(gasUsed, gasTarget, baseFeeChangeDenom uint64,
                      baseFee, minUnitGas, minGasPrice LegacyDec) LegacyDec {
      // No change if at target
      if gasUsed == gasTarget {
          return baseFee
      }

      // Calculate adjustment magnitude
      delta := abs(gasUsed - gasTarget)
      adjustment := baseFee.Mul(delta).Quo(gasTarget).Quo(baseFeeChangeDenom)

      if gasUsed > gasTarget {
          // Increase base fee (minimum 1 unit)
          baseFeeDelta := MaxDec(adjustment, minUnitGas)
          return baseFee.Add(baseFeeDelta)
      } else {
          // Decrease base fee (not below minGasPrice)
          return MaxDec(baseFee.Sub(adjustment), minGasPrice)
      }
  }
  ```

  The `minUnitGas` is calculated as `1 / 10^decimals` to ensure minimum increments based on token precision ([source](https://github.com/cosmos/evm/blob/v0.4.1/utils/utils.go#L229-L254)).
</Expandable>

### Keeper

The keeper manages fee market state and calculations ([source](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/keeper.go)):

| Method                                        | Description           | Usage                               |
| --------------------------------------------- | --------------------- | ----------------------------------- |
| `GetBaseFee()` / `SetBaseFee()`               | Current base fee      | Read/update during block processing |
| `GetParams()` / `SetParams()`                 | Module parameters     | Governance updates                  |
| `GetBlockGasWanted()` / `SetBlockGasWanted()` | Gas tracking          | Base fee calculation                |
| `CalculateBaseFee()`                          | Compute next base fee | Called in BeginBlock                |

The module also implements `PostTxProcessing` hooks for EVM transaction processing ([source](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/hooks.go)).

### Events

The module emits the following events ([types](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/types/events.go)):

#### Fee Market Block Fees

| Attribute Key | Attribute Value           |
| ------------- | ------------------------- |
| height        | Current block height      |
| base\_fee     | New base fee              |
| gas\_wanted   | Total gas wanted in block |
| gas\_used     | Total gas used in block   |

Example:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "type": "fee_market_block_fees",
  "attributes": [
    {"key": "height", "value": "12345"},
    {"key": "base_fee", "value": "1000000000"},
    {"key": "gas_wanted", "value": "5000000"},
    {"key": "gas_used", "value": "4800000"}
  ]
}
```

### AnteHandlers

The module integrates with EVM transactions through the `EVMMonoDecorator`, which performs all fee-related validations in a single pass ([source](https://github.com/cosmos/evm/blob/v0.4.1/ante/evm/mono_decorator.go#L50-L252)):

#### EVMMonoDecorator

The primary ante handler that validates and processes EVM transaction fees ([mono\_decorator.go](https://github.com/cosmos/evm/blob/v0.4.1/ante/evm/mono_decorator.go)):

<Expandable title="Key validation steps">
  ```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  // 1. Check mempool minimum fee (for pre-London transactions)
  if ctx.IsCheckTx() && !simulate && !isLondon {
      requiredFee := mempoolMinGasPrice.Mul(gasLimit)
      if fee.LT(requiredFee) {
          return ErrInsufficientFee
      }
  }

  // 2. Calculate effective fee for EIP-1559 transactions
  if ethTx.Type() >= DynamicFeeTxType && baseFee != nil {
      feeAmt = ethMsg.GetEffectiveFee(baseFee)
      fee = NewDecFromBigInt(feeAmt)
  }

  // 3. Check global minimum gas price
  if globalMinGasPrice.IsPositive() {
      requiredFee := globalMinGasPrice.Mul(gasLimit)
      if fee.LT(requiredFee) {
          return ErrInsufficientFee
      }
  }

  // 4. Track gas wanted for base fee calculation
  if isLondon && baseFeeEnabled {
      feeMarketKeeper.AddTransientGasWanted(ctx, gasWanted)
  }
  ```
</Expandable>

#### Fee Validation Functions

##### CheckMempoolFee

Validates transaction fees against the local mempool minimum ([source](https://github.com/cosmos/evm/blob/v0.4.1/ante/evm/02_mempool_fee.go#L13-L29)):

<Expandable title="Implementation details">
  ```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  func CheckMempoolFee(fee, mempoolMinGasPrice, gasLimit LegacyDec, isLondon bool) error {
      // Skip for London-enabled chains (EIP-1559 handles this)
      if isLondon {
          return nil
      }

      requiredFee := mempoolMinGasPrice.Mul(gasLimit)
      if fee.LT(requiredFee) {
          return ErrInsufficientFee
      }
      return nil
  }
  ```

  **Note**: This check is bypassed for London-enabled chains since EIP-1559 base fee mechanism handles minimum pricing.
</Expandable>

##### CheckGlobalFee

Enforces the chain-wide minimum gas price set via governance ([source](https://github.com/cosmos/evm/blob/v0.4.1/ante/evm/03_global_fee.go#L20-L36)):

<Expandable title="Implementation details">
  ```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  func CheckGlobalFee(fee, globalMinGasPrice, gasLimit LegacyDec) error {
      if globalMinGasPrice.IsZero() {
          return nil
      }

      requiredFee := globalMinGasPrice.Mul(gasLimit)
      if fee.LT(requiredFee) {
          return ErrInsufficientFee
      }
      return nil
  }
  ```

  For EIP-1559 transactions, if the effective price falls below `MinGasPrice`, users must increase the priority fee (tip) until the effective price meets the minimum.

  In cosmos/evm's experimental mempool, transactions are ordered by effective gas tip (calculated as `min(maxPriorityFeePerGas, maxFeePerGas - baseFee)`), with higher tips getting priority. When tips are equal, transactions are ordered by arrival time ([source](https://github.com/cosmos/evm/blob/v0.4.1/mempool/miner/ordering.go#L63-L71)).
</Expandable>

##### CheckGasWanted

Tracks cumulative gas wanted for base fee calculation ([source](https://github.com/cosmos/evm/blob/v0.4.1/ante/evm/10_gas_wanted.go#L48-L82)):

<Expandable title="Implementation details">
  ```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
  func CheckGasWanted(ctx Context, feeMarketKeeper FeeMarketKeeper, tx Tx, isLondon bool) error {
      if !isLondon || !feeMarketKeeper.GetBaseFeeEnabled(ctx) {
          return nil
      }

      gasWanted := tx.GetGas()
      blockGasLimit := BlockGasLimit(ctx)

      // Reject if tx exceeds block limit
      if gasWanted > blockGasLimit {
          return ErrOutOfGas
      }

      // Add to cumulative gas wanted for base fee adjustment
      feeMarketKeeper.AddTransientGasWanted(ctx, gasWanted)
      return nil
  }
  ```

  This cumulative gas wanted is used at the end of the block to calculate the next block's base fee.
</Expandable>

## Module Distinctions

### cosmos/evm vs Standard Cosmos SDK

This fee market module from [cosmos/evm](https://github.com/cosmos/evm/tree/v0.4.1/x/feemarket) differs from standard Cosmos SDK fee handling:

| **Aspect**            | **Standard Cosmos SDK**                     | **cosmos/evm Feemarket**                  |
| --------------------- | ------------------------------------------- | ----------------------------------------- |
| **Fee Model**         | Static, validator-configured min gas prices | Dynamic EIP-1559 base fee                 |
| **Price Discovery**   | Manual adjustment by validators             | Automatic based on utilization            |
| **Transaction Types** | Cosmos SDK Tx only                          | Both Cosmos & Ethereum txs                |
| **Decimal Handling**  | Chain-specific precision                    | 18-decimal EVM compatibility              |
| **State Storage**     | Not tracked                                 | Base fee in state, gas in transient store |
| **Consensus Impact**  | No consensus on fees                        | Base fee part of consensus                |

### Key Integration Points

The module integrates with EVM through:

* **AnteHandlers**: Custom decorators for EVM transaction validation ([source](https://github.com/cosmos/evm/blob/v0.4.1/ante/evm/))
* **Hooks**: PostTxProcessing for EVM state updates ([source](https://github.com/cosmos/evm/blob/v0.4.1/x/feemarket/keeper/hooks.go))
* **RPC**: Ethereum JSON-RPC methods for fee queries ([source](https://github.com/cosmos/evm/blob/v0.4.1/rpc/backend/chain_info.go))

## References

### Source Code

* [cosmos/evm Fee Market Module](https://github.com/cosmos/evm/tree/v0.4.1/x/feemarket) - Main module implementation
* [AnteHandlers](https://github.com/cosmos/evm/tree/v0.4.1/ante/evm) - EVM transaction validation
* [Proto Definitions](https://github.com/cosmos/evm/tree/v0.4.1/proto/cosmos/evm/feemarket/v1) - API and state structures
* [RPC Implementation](https://github.com/cosmos/evm/tree/v0.4.1/rpc/backend) - Ethereum JSON-RPC support

### Specifications

* [EIP-1559 Specification](https://eips.ethereum.org/EIPS/eip-1559) - Original Ethereum proposal
* [Cosmos SDK Docs](https://docs.cosmos.network) - Base framework documentation

### Tools & Libraries

* [Ethereum Gas Tracker](https://etherscan.io/gastracker) - Real-time Ethereum gas prices
* [Web3.js EIP-1559 Support](https://web3js.readthedocs.io/en/v1.7.0/web3-eth.html#id81) - JavaScript integration
* [Ethers.js Fee Data](https://docs.ethers.io/v5/api/providers/provider/#Provider-getFeeData) - TypeScript/JavaScript library