> ## 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

# Fee Market Module Reference

The Fee Market module (`x/feemarket`) implements EIP-1559 dynamic fee pricing, enabling base fee adjustment based on block utilization. This provides better fee predictability and network congestion management compared to static gas pricing.

## Module Overview

**Purpose**: Implement EIP-1559 dynamic fee market mechanism for EVM transactions

**Key Functionality**:

* Dynamic base fee calculation based on block gas usage
* EIP-1559 base fee per gas with automatic adjustment
* Priority fee (tip) support for transaction ordering
* Minimum gas price enforcement
* Configurable elasticity for block gas limits
* Fee burning mechanism (base fee is burned)

**Source Code**: [x/feemarket](https://github.com/cosmos/evm/tree/main/x/feemarket)
**Parameter Defaults**: [x/feemarket/types/params.go](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go)

***

## EIP-1559 Overview

EIP-1559 introduces a dynamic fee structure:

**Transaction Fee Components**:

* **Base Fee**: Algorithmically determined fee per gas unit (burned)
* **Priority Fee (Tip)**: Optional additional fee paid to validators
* **Max Fee**: Maximum fee per gas the user is willing to pay

**Fee Calculation**:

```
effective_gas_price = base_fee + priority_fee
total_fee = gas_used * effective_gas_price
```

**Base Fee Adjustment**:

* Block > target gas: Base fee increases (up to 12.5% per block with default settings)
* Block \< target gas: Base fee decreases (down to 12.5% per block)
* Block = target gas: Base fee remains constant

**Benefits**:

* Predictable fees for users (base fee visible before transaction)
* Automatic congestion response (fees rise when busy, fall when quiet)
* MEV reduction (base fee not capturable by validators)
* Better UX (wallets can show reliable fee estimates)

***

## Configuration Methods

The Fee Market module is configured through genesis.json before chain launch. Fee market parameters have defaults and typically don't require modification in local\_node.sh unless testing specific scenarios.

### Method 1: Direct JSON Editing

Edit `~/.evmd/config/genesis.json` directly:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "app_state": {
    "feemarket": {
      "params": {
        "no_base_fee": false,
        "base_fee": "1000000000",
        "base_fee_change_denominator": 8,
        "elasticity_multiplier": 2,
        "enable_height": 0,
        "min_gas_price": "0",
        "min_gas_multiplier": "0.5"
      }
    }
  }
}
```

### Method 2: Using jq Command-Line Tool

Programmatically modify genesis using jq:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
GENESIS="$HOME/.evmd/config/genesis.json"
TMP_GENESIS="$HOME/.evmd/config/tmp_genesis.json"

# Disable EIP-1559 (use fixed gas pricing)
jq '.app_state["feemarket"]["params"]["no_base_fee"]=true' "$GENESIS" >"$TMP_GENESIS" && mv "$TMP_GENESIS" "$GENESIS"

# Set initial base fee (1 gwei)
jq '.app_state["feemarket"]["params"]["base_fee"]="1000000000"' "$GENESIS" >"$TMP_GENESIS" && mv "$TMP_GENESIS" "$GENESIS"

# Adjust base fee change speed (slower adjustment)
jq '.app_state["feemarket"]["params"]["base_fee_change_denominator"]=50' "$GENESIS" >"$TMP_GENESIS" && mv "$TMP_GENESIS" "$GENESIS"

# Set minimum gas price floor (0.5 gwei)
jq '.app_state["feemarket"]["params"]["min_gas_price"]="500000000"' "$GENESIS" >"$TMP_GENESIS" && mv "$TMP_GENESIS" "$GENESIS"
```

### Method 3: Runtime Configuration

Fee market behavior can also be influenced at node startup via app.toml:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# In app.toml - sets node-level minimum (separate from consensus param)
minimum-gas-prices = "1000000000atest"  # 1 gwei minimum
```

**Note**: The `minimum-gas-prices` in app.toml is a node-level filter. Genesis params are consensus-level and apply chain-wide.

***

## Parameters

### no\_base\_fee

**What It Does**: Completely disables the EIP-1559 dynamic base fee mechanism. When true, the chain uses only `min_gas_price` as a fixed minimum fee.

**Type**: `bool`

**Valid Values**:

* `false` - Enable EIP-1559 dynamic base fee (recommended, Ethereum-compatible)
* `true` - Disable EIP-1559, use fixed min\_gas\_price only (pre-London behavior)

**Default**: `false` ([params.go:21](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L21))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - Disable EIP-1559
jq '.app_state["feemarket"]["params"]["no_base_fee"]=true' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "no_base_fee": true
    }
  }
}
```

**Impact**:

**When false (EIP-1559 enabled)**:

* Base fee adjusts dynamically based on block utilization
* Better fee predictability for users
* Automatic congestion management
* Base fee is burned (deflationary pressure)
* Standard Ethereum behavior

**When true (EIP-1559 disabled)**:

* Simple fixed minimum gas price
* Easier to understand for some users
* No dynamic adjustment to congestion
* All fees go to validators (no burning)
* Pre-London Ethereum behavior

**Use Cases**:

* `false` - Recommended for production chains, Ethereum compatibility
* `true` - Simplified fee model for private chains or specific use cases

**Compatibility Note**: Setting to `true` breaks Ethereum EIP-1559 transaction compatibility. Modern wallets expect dynamic fees.

***

### base\_fee

**What It Does**: Sets the initial base fee per gas in wei at genesis. This is the starting point for EIP-1559 base fee algorithm.

**Type**: `string` (decimal number representing wei)

**Valid Values**: Any non-negative decimal value in wei

**Default**: `"1000000000"` (1 gwei, [params.go:13](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L13))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - Set to 10 gwei
jq '.app_state["feemarket"]["params"]["base_fee"]="10000000000"' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "base_fee": "10000000000"
    }
  }
}
```

**Common Values**:

* `"100000000"` (0.1 gwei) - Very low for testnets or L2s
* `"1000000000"` (1 gwei) - Default, good starting point
* `"10000000000"` (10 gwei) - Higher initial fee for expected high demand
* `"100000000000"` (100 gwei) - Very high for mainnet launch with known demand

**Impact**:

* Sets initial transaction costs at chain launch
* Adjusts up/down automatically after genesis based on block utilization
* Should align with expected network usage and token economics
* Too low: May cause congestion at launch
* Too high: May deter early adoption

**Recommendations**:

* **Testnet**: 0.1-1 gwei (low cost for testing)
* **L2/App-specific**: 0.1-1 gwei (optimize for low fees)
* **General Purpose L1**: 1-10 gwei (balanced)
* **High Demand Launch**: 10-100 gwei (prevent spam)

**Validation**: Must be non-negative ([params.go:66-68](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L66-L68))

**Related**: Works with `enable_height` to delay EIP-1559 activation

***

### base\_fee\_change\_denominator

**What It Does**: Controls how quickly the base fee can change per block. Acts as the denominator in the base fee change calculation.

**Type**: `uint32`

**Valid Values**: Any positive integer (cannot be 0)

**Default**: `8` (standard EIP-1559, from go-ethereum params, [params.go:51](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L51))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - Slower adjustment (±2% per block)
jq '.app_state["feemarket"]["params"]["base_fee_change_denominator"]=50' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "base_fee_change_denominator": 8
    }
  }
}
```

**How It Works**:

The maximum base fee change per block is calculated as:

```
max_change_per_block = base_fee / base_fee_change_denominator
```

**Common Values**:

| Value | Max Change/Block | Description                                 |
| ----- | ---------------- | ------------------------------------------- |
| `4`   | ±25%             | Fast adjustment (2x change in \~3 blocks)   |
| `8`   | ±12.5%           | Standard EIP-1559 (2x change in \~6 blocks) |
| `16`  | ±6.25%           | Slower (2x change in \~12 blocks)           |
| `50`  | ±2%              | Very slow (2x change in \~35 blocks)        |
| `100` | ±1%              | Extremely slow (2x change in \~70 blocks)   |

**Impact**:

**Lower Denominator (faster adjustment)**:

* Pros: Responds quickly to sudden traffic spikes, less predictable attack surface
* Cons: More volatile fees, harder to predict costs, potential for rapid increases

**Higher Denominator (slower adjustment)**:

* Pros: More stable fees, better predictability, smoother UX
* Cons: Slower response to congestion, takes longer to reach equilibrium

**Recommendations**:

* **Standard chains**: `8` (matches Ethereum mainnet)
* **High-throughput chains**: `4-8` (faster response to varying load)
* **Stable fee chains**: `16-50` (prioritize predictability)
* **Private networks**: `100+` (minimal fee variation)

**Example Scenarios**:

With `denominator=8`, starting from 10 gwei base fee:

* Block 100% full: Next base fee = 11.25 gwei (+12.5%)
* Block 50% full (target): Next base fee = 10 gwei (unchanged)
* Block 0% full: Next base fee = 8.75 gwei (-12.5%)

With `denominator=50`, same conditions:

* Block 100% full: Next base fee = 10.2 gwei (+2%)
* Block 0% full: Next base fee = 9.8 gwei (-2%)

**Validation**: Cannot be 0 ([params.go:62-64](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L62-L64))

**Related**: Works with `elasticity_multiplier` to determine target gas usage

***

### elasticity\_multiplier

**What It Does**: Defines the maximum block gas limit as a multiple of target gas. Allows blocks to temporarily exceed target during high demand.

**Type**: `uint32`

**Valid Values**: Any positive integer (cannot be 0)

**Default**: `2` (standard EIP-1559, from go-ethereum params, [params.go:52](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L52))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - More elastic (3x target)
jq '.app_state["feemarket"]["params"]["elasticity_multiplier"]=3' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "elasticity_multiplier": 2
    }
  }
}
```

**How It Works**:

```
target_gas = block_gas_limit / elasticity_multiplier
max_block_gas = target_gas * elasticity_multiplier
```

With elasticity\_multiplier = 2:

* If block gas limit is 30M gas
* Target gas per block = 15M gas
* Maximum gas per block = 30M gas (2x target)

**Base Fee Adjustment Logic**:

* Block gas used > target gas → Base fee increases
* Block gas used = target gas → Base fee stays constant
* Block gas used \< target gas → Base fee decreases

**Common Values**:

| Value | Description                           | Use Case                                |
| ----- | ------------------------------------- | --------------------------------------- |
| `1`   | No elasticity (hard limit = target)   | Strictly controlled throughput          |
| `2`   | Standard EIP-1559 (2x burst capacity) | Balanced flexibility (Ethereum mainnet) |
| `3`   | Higher elasticity (3x burst capacity) | High-variance workloads                 |
| `4+`  | Very elastic                          | Extreme burst tolerance                 |

**Impact**:

**Lower Multiplier (1-2)**:

* Pros: More predictable block sizes, easier to provision resources
* Cons: Less burst capacity, may reject transactions during spikes

**Higher Multiplier (3-4+)**:

* Pros: Better handles traffic spikes, fewer transaction rejections
* Cons: More variable block sizes, requires higher validator specs, longer block times

**Example with multiplier=2**:

* Block gas limit: 30M gas
* Target: 15M gas
* If block uses 20M gas (above target): Base fee increases
* If block uses 10M gas (below target): Base fee decreases
* If block uses 15M gas (at target): Base fee unchanged

**Recommendations**:

* **Standard chains**: `2` (matches Ethereum mainnet)
* **High-throughput chains**: `2-3` (handle variable load)
* **Resource-constrained chains**: `1-2` (predictable requirements)
* **Burst-heavy chains**: `3-4` (accommodate spikes)

**Validation**: Cannot be 0 ([params.go:74-76](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L74-L76))

**Related**: Interacts with consensus param `block.max_gas` which sets the absolute maximum

***

### enable\_height

**What It Does**: Block height at which EIP-1559 base fee mechanism activates. Useful for coordinated mainnet upgrades to enable EIP-1559 after launch.

**Type**: `int64`

**Valid Values**: Any non-negative integer

**Default**: `0` (enabled from genesis, [params.go:19](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L19))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - Enable EIP-1559 at block 100000
jq '.app_state["feemarket"]["params"]["enable_height"]=100000' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "enable_height": 0
    }
  }
}
```

**Common Values**:

* `0` - Enable from genesis (recommended for new chains)
* `100000` - Enable at specific future block height
* `-1` or very large number - Effectively disabled (use `no_base_fee` instead)

**Impact**:

**Before enable\_height**:

* Base fee mechanism is inactive
* Falls back to `min_gas_price` behavior
* Transactions use pre-EIP-1559 gas pricing

**At and after enable\_height**:

* Base fee mechanism activates
* Dynamic fee adjustment begins
* Transactions must use EIP-1559 fee structure

**Use Cases**:

**New Chain (enable\_height=0)**:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "enable_height": 0,
  "base_fee": "1000000000"
}
```

* EIP-1559 active from block 1
* Recommended for new chains

**Coordinated Upgrade (enable\_height=100000)**:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "enable_height": 100000,
  "base_fee": "5000000000"
}
```

* Chain launches with fixed fees
* Switches to dynamic fees at block 100000
* Allows testing before enabling
* All validators must be ready by block 100000

**Recommendations**:

* **New chains**: Set to `0` (enable from start)
* **Existing chains**: Use governance + hard fork to change (cannot be done via enable\_height after launch)
* **Testing**: Use specific block height to test fee market behavior

**Validation**: Cannot be negative ([params.go:70-72](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L70-L72))

**Important**: This parameter is checked at each block. Setting it in genesis affects when the module begins calculating base fees.

***

### min\_gas\_price

**What It Does**: Sets a global minimum gas price floor in native token decimals. Provides an absolute minimum fee even if the dynamic base fee drops lower.

**Type**: `string` (decimal value)

**Valid Values**: Any non-negative decimal value

**Default**: `"0"` (disabled, [params.go:17](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L17))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - Set 0.5 gwei minimum
jq '.app_state["feemarket"]["params"]["min_gas_price"]="500000000"' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "min_gas_price": "500000000"
    }
  }
}
```

**Common Values**:

* `"0"` - No minimum floor (rely on base fee only, default)
* `"1000000000"` - 1 gwei minimum floor
* `"10000000000"` - 10 gwei minimum floor
* `"100000000"` - 0.1 gwei minimum for low-fee chains

**How It Works**:

```
effective_minimum = max(min_gas_price, base_fee * min_gas_multiplier)
if base_fee < effective_minimum:
    use effective_minimum
else:
    use base_fee
```

**Impact**:

**When min\_gas\_price = 0 (default)**:

* Base fee can fall arbitrarily low during quiet periods
* Purely market-driven pricing
* May approach 0 on idle chains
* Standard Ethereum behavior

**When min\_gas\_price > 0**:

* Prevents fees from falling below floor
* Protects against spam during quiet periods
* Creates fixed revenue for validators even at low usage
* May discourage usage if set too high

**Use Cases**:

**Public Chain (min\_gas\_price=0)**:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "min_gas_price": "0",
  "min_gas_multiplier": "0.5"
}
```

* Pure EIP-1559 with no floor
* Fees determined entirely by supply/demand
* Recommended for Ethereum compatibility

**Spam Protection (min\_gas\_price=1000000000)**:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "min_gas_price": "1000000000",
  "min_gas_multiplier": "0"
}
```

* 1 gwei absolute minimum
* Prevents fee races to zero
* Good for chains that want cost floor

**Low-Fee L2 (min\_gas\_price=100000000)**:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "min_gas_price": "100000000",
  "min_gas_multiplier": "0"
}
```

* 0.1 gwei minimum
* Cheap transactions guaranteed
* Suitable for high-throughput chains

**Recommendations**:

* **Ethereum-compatible chains**: `"0"` (no floor)
* **Anti-spam focus**: `"1000000000"` - `"10000000000"` (1-10 gwei)
* **Low-fee chains**: `"100000000"` (0.1 gwei)
* **Private chains**: Higher values to prevent test spam

**Validation**: Must be non-negative ([params.go:89-98](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L89-L98))

**Node-Level Minimum**: Remember that nodes can also set `minimum-gas-prices` in app.toml, which filters transactions locally before consensus.

***

### min\_gas\_multiplier

**What It Does**: Fraction of base fee to use as the effective minimum gas price. Creates a dynamic minimum that scales with base fee.

**Type**: `string` (decimal value between 0 and 1)

**Valid Values**: Decimal between `0` and `1` (inclusive)

**Default**: `"0.5"` (50% of base fee, [params.go:15](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L15))

**Configuration**:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Using jq - Set to 80% of base fee
jq '.app_state["feemarket"]["params"]["min_gas_multiplier"]="0.8"' genesis.json > tmp.json && mv tmp.json genesis.json
```

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "min_gas_multiplier": "0.5"
    }
  }
}
```

**How It Works**:

```
effective_minimum = max(min_gas_price, base_fee * min_gas_multiplier)
```

If base fee is 10 gwei and min\_gas\_multiplier is 0.5:

* Effective minimum = 5 gwei
* Transactions below 5 gwei are rejected
* Even if base fee drops to 8 gwei next block, minimum becomes 4 gwei

**Common Values**:

| Value   | Meaning                     | Use Case                     |
| ------- | --------------------------- | ---------------------------- |
| `"0"`   | No multiplier-based minimum | Rely only on `min_gas_price` |
| `"0.5"` | 50% of base fee (default)   | Balanced protection          |
| `"0.8"` | 80% of base fee             | Stricter minimum             |
| `"1.0"` | 100% of base fee            | Force exact base fee payment |

**Impact**:

**Lower Multiplier (0-0.5)**:

* Allows transactions with lower gas prices relative to base fee
* More forgiving for users during fee spikes
* May allow some low-fee spam
* Better for adoption

**Higher Multiplier (0.5-1.0)**:

* Stricter minimum gas price requirements
* Better spam protection
* May frustrate users who try to pay slightly below base fee
* Forces full EIP-1559 fee payment

**Examples**:

**Default (min\_gas\_multiplier=0.5)**:

* Base fee = 10 gwei → Minimum = 5 gwei
* Base fee = 100 gwei → Minimum = 50 gwei
* Scales with congestion, always accepts at least 50% of base fee

**Strict (min\_gas\_multiplier=1.0)**:

* Base fee = 10 gwei → Minimum = 10 gwei
* Forces exact base fee payment
* No transactions accepted below current base fee

**Permissive (min\_gas\_multiplier=0)**:

* Minimum determined only by `min_gas_price`
* If `min_gas_price=0`, can accept very low fees
* High spam risk

**Recommendations**:

* **Standard chains**: `"0.5"` (default, good balance)
* **High-value chains**: `"0.8"` - `"1.0"` (strict enforcement)
* **Spam-prone chains**: `"0.8"` - `"1.0"` (better protection)
* **Low-fee L2s**: `"0"` - `"0.3"` (maximize accessibility)

**Validation**: Must be between 0 and 1 inclusive ([params.go:101-114](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go#L101-L114))

**Interaction**: Works together with `min_gas_price`. The effective minimum is the maximum of both values.

***

## Complete Configuration Examples

### Standard EIP-1559 Configuration (Recommended)

Based on Ethereum mainnet defaults:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "no_base_fee": false,
      "base_fee": "1000000000",
      "base_fee_change_denominator": 8,
      "elasticity_multiplier": 2,
      "enable_height": 0,
      "min_gas_price": "0",
      "min_gas_multiplier": "0.5"
    }
  }
}
```

Using jq:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
GENESIS="$HOME/.evmd/config/genesis.json"
TMP="$HOME/.evmd/config/tmp_genesis.json"

jq '.app_state["feemarket"]["params"]["no_base_fee"]=false' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
jq '.app_state["feemarket"]["params"]["base_fee"]="1000000000"' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
jq '.app_state["feemarket"]["params"]["base_fee_change_denominator"]=8' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
jq '.app_state["feemarket"]["params"]["elasticity_multiplier"]=2' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
jq '.app_state["feemarket"]["params"]["enable_height"]=0' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
jq '.app_state["feemarket"]["params"]["min_gas_price"]="0"' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
jq '.app_state["feemarket"]["params"]["min_gas_multiplier"]="0.5"' "$GENESIS" >"$TMP" && mv "$TMP" "$GENESIS"
```

### Low-Fee L2 Configuration

Optimized for low transaction costs:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "no_base_fee": false,
      "base_fee": "100000000",
      "base_fee_change_denominator": 16,
      "elasticity_multiplier": 3,
      "enable_height": 0,
      "min_gas_price": "100000000",
      "min_gas_multiplier": "0.3"
    }
  }
}
```

### Fixed Fee Configuration (Disabled EIP-1559)

Simple fixed pricing model:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "no_base_fee": true,
      "base_fee": "0",
      "base_fee_change_denominator": 8,
      "elasticity_multiplier": 2,
      "enable_height": 0,
      "min_gas_price": "1000000000",
      "min_gas_multiplier": "0"
    }
  }
}
```

### High-Stability Configuration

Minimal fee volatility:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
  "feemarket": {
    "params": {
      "no_base_fee": false,
      "base_fee": "10000000000",
      "base_fee_change_denominator": 50,
      "elasticity_multiplier": 2,
      "enable_height": 0,
      "min_gas_price": "5000000000",
      "min_gas_multiplier": "0.8"
    }
  }
}
```

***

## Runtime Configuration (app.toml)

In addition to genesis parameters, individual nodes can set minimum gas prices in app.toml:

```toml theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# app.toml
[json-rpc]
# Node will reject transactions below this price
minimum-gas-prices = "1000000000atest"  # 1 gwei in atest token

# Minimum priority fee for mempool ordering
evm-timeout = "5s"
evm-max-tx-gas-wanted = 0
```

**Important Distinction**:

* **Genesis params** (feemarket module): Consensus-level, enforced by all validators
* **app.toml params**: Node-level filter, can vary per node

Node-level `minimum-gas-prices` must be >= consensus-level minimum or the node will fail to produce valid blocks.

***

## Monitoring and Adjusting

### Query Current Base Fee

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Query current base fee
evmd query feemarket base-fee

# Query all fee market params
evmd query feemarket params
```

### Via JSON-RPC

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Get current base fee via eth_gasPrice
curl -X POST http://localhost:8545 -H "Content-Type: application/json" \
  --data '{"jsonrpc":"2.0","method":"eth_gasPrice","params":[],"id":1}'

# Get specific block's base fee
curl -X POST http://localhost:8545 -H "Content-Type: application/json" \
  --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest",false],"id":1}' \
  | jq '.result.baseFeePerGas'
```

### Governance Updates

Fee market parameters can be updated via governance proposals after launch:

```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
# Example: Update base_fee_change_denominator to 50 (slower adjustment)
evmd tx gov submit-proposal param-change proposal.json --from validator --chain-id mychain-1

# proposal.json
{
  "title": "Slow Down Base Fee Adjustment",
  "description": "Reduce base fee volatility by setting denominator to 50",
  "changes": [
    {
      "subspace": "feemarket",
      "key": "BaseFeeChangeDenominator",
      "value": "50"
    }
  ],
  "deposit": "10000000atest"
}
```

***

## Common Issues and Solutions

### Issue: Transactions Fail with "Gas Price Too Low"

**Cause**: Transaction gas price \< effective minimum (base\_fee or min\_gas\_price)

**Solution**:

* Check current base fee: `evmd query feemarket base-fee`
* Ensure wallet uses EIP-1559 transaction type
* Set `maxFeePerGas` >= current base fee + desired priority fee
* Check node's `minimum-gas-prices` in app.toml

### Issue: Base Fee Too Volatile

**Cause**: `base_fee_change_denominator` too low (fast adjustment)

**Solution**:

* Increase `base_fee_change_denominator` (e.g., from 8 to 50)
* Requires governance proposal to change after launch
* Plan for this in genesis if predictable fees are critical

### Issue: Network Congestion Not Responding

**Cause**: `base_fee_change_denominator` too high (slow adjustment)

**Solution**:

* Decrease `base_fee_change_denominator` for faster response
* Increase `elasticity_multiplier` to allow bigger blocks during spikes
* Requires governance proposal after launch

### Issue: Fees Never Decrease

**Cause**: Blocks consistently above target gas

**Solution**:

* Check if `elasticity_multiplier` is appropriate for traffic pattern
* Consider increasing block gas limit in consensus params
* Evaluate if chain throughput needs scaling

***

## Related Documentation

* [Building Your Chain Guide](/evm/v0.5.0/documentation/getting-started/build-a-chain/overview) - Main configuration walkthrough
* [Chain Customization Checklist](/evm/v0.5.0/documentation/getting-started/build-a-chain/quick-start) - Complete parameter checklist
* [VM Module](/evm/v0.5.0/documentation/cosmos-sdk/modules/vm) - EVM configuration
* [Token Configuration Guide](/evm/v0.5.0/documentation/getting-started/build-a-chain/quick-start) - Token economics setup
* [EIP-1559 Specification](https://eips.ethereum.org/EIPS/eip-1559) - Original Ethereum proposal

***

## Source Code References

* **Module Implementation**: [x/feemarket](https://github.com/cosmos/evm/tree/main/x/feemarket)
* **Parameter Types**: [x/feemarket/types/params.go](https://github.com/cosmos/evm/blob/main/x/feemarket/types/params.go)
* **Keeper Logic**: [x/feemarket/keeper](https://github.com/cosmos/evm/tree/main/x/feemarket/keeper)
* **Genesis Setup**: [local\_node.sh](https://github.com/cosmos/evm/blob/main/local_node.sh) (feemarket uses defaults)