How the Forge ZSH Theme Displays Cost Information: Environment Variable Configuration

The Forge ZSH theme displays session cost in your terminal's right prompt by multiplying raw USD costs by the FORGE_CURRENCY_CONVERSION_RATE and prefixing the result with the FORGE_CURRENCY_SYMBOL, both controlled through environment variables in the antinomyhq/forgecode repository.

The Forge ZSH theme provides real-time cost visibility for AI-powered coding sessions by rendering token usage and associated costs directly in your terminal's right prompt. This functionality is implemented in the ZshRPrompt struct within the antinomyhq/forgecode codebase, which conditionally formats cost information only when active sessions have non-zero token counts and associated cost data from the provider.

How Cost Information Appears in the Right Prompt

The right prompt (RPROMPT) integration resides in crates/forge_main/src/zsh/rprompt.rs, where the ZshRPrompt struct handles all formatting logic. When a session has a non-zero token count, the prompt displays three elements: an agent icon with name, the token count, and the session cost.

The ZshRPrompt Struct

The ZshRPrompt struct is defined in crates/forge_main/src/zsh/rprompt.rs and manages the visual presentation of session metadata. It stores the currency_symbol as a String and the conversion_ratio as a decimal value that transforms the raw cost before display.

Conditional Cost Rendering Logic

Cost information appears only when both conditions are met: the session contains tokens (active is true) and the cost field contains a value. The rendering logic at lines 100-107 of rprompt.rs implements this check:

// crates/forge_main/src/zsh/rprompt.rs (lines 100-107)
if let Some(cost) = self.cost && active {
    let converted_cost = cost * self.conversion_ratio;
    let cost_str = format!("{}{:.2}", self.currency_symbol, converted_cost);
    write!(f, " {}", cost_str.zsh().fg(ZshColor::GREEN).bold())?;
}

This code multiplies the raw cost by the conversion_ratio, formats the result to two decimal places with the currency_symbol prefix, and applies green bold styling before appending it to the prompt.

Environment Variables That Control Currency Display

Two specific environment variables control how costs are presented in the ZSH theme. These values populate the ForgeConfig struct defined in crates/forge_config/src/config.rs (lines 269-279) and are accessed by ZshRPrompt::from_config at lines 39-45 of rprompt.rs.

FORGE_CURRENCY_SYMBOL

The FORGE_CURRENCY_SYMBOL environment variable sets the currency_symbol field in the configuration, defaulting to "$" when unset. This symbol prefixes the converted cost value in the right prompt display.

FORGE_CURRENCY_CONVERSION_RATE

The FORGE_CURRENCY_CONVERSION_RATE environment variable controls the currency_conversion_rate field, defaulting to 1.0. This decimal multiplier converts the raw USD cost (as returned by the API) to your preferred currency denomination before formatting.

The from_config method in ZshRPrompt demonstrates how these configuration values bridge the global configuration and the display layer:

// crates/forge_main/src/zsh/rprompt.rs (lines 39-45)
pub fn from_config(config: &ForgeConfig) -> Self {
    Self::default()
        .currency_symbol(config.currency_symbol.clone())
        .conversion_ratio(config.currency_conversion_rate.value())
}

Practical Configuration Examples

The following examples demonstrate how to configure the Forge ZSH theme for different currency displays using environment variables.

Default USD Display

With no environment variables set, the theme defaults to USD with a conversion rate of 1.0:

# Default configuration

forge commit

# RPROMPT displays:   FORGE 1.5k $0.01  gpt-4

The $0.01 indicates the raw USD cost multiplied by 1.0 and prefixed with the default $ symbol.

Displaying Costs in Indian Rupees

To display costs in INR with an appropriate conversion rate:

export FORGE_CURRENCY_SYMBOL="₹"
export FORGE_CURRENCY_CONVERSION_RATE=83.5

forge commit

# RPROMPT displays:   FORGE 1.5k ₹0.83  gpt-4

A raw cost of $0.01 becomes ₹0.83 after multiplication by 83.5 and rounding to two decimal places.

Disabling Nerd Fonts While Preserving Currency

The currency display operates independently of Nerd Font icons. Disabling Nerd Fonts affects agent and model icons but leaves cost formatting intact:

export NERD_FONT=0
export FORGE_CURRENCY_SYMBOL="€"
export FORGE_CURRENCY_CONVERSION_RATE=0.92

forge commit

# RPROMPT displays:  FORGE 1.5k €0.01 gpt-4

Sessions Without Cost Data

When the provider does not return cost information, the currency section is omitted entirely while other elements remain:

forge command-with-no-cost

# RPROMPT displays:   FORGE 2.3k   gpt-4

# Note the absence of the currency segment

Summary

• The Forge ZSH theme displays session costs in the right prompt via the ZshRPrompt struct in crates/forge_main/src/zsh/rprompt.rs.
• Cost display requires both an active session (non-zero tokens) and a populated cost field from the provider.
• FORGE_CURRENCY_SYMBOL controls the currency prefix (default: "$").
• FORGE_CURRENCY_CONVERSION_RATE multiplies the raw USD cost before display (default: 1.0).
• The conversion formula cost * conversion_ratio produces the final displayed value, formatted to two decimal places with green bold styling.
• Currency display is independent of Nerd Font settings (NERD_FONT or USE_NERD_FONT).

Frequently Asked Questions

How do I change the currency symbol in the Forge ZSH theme?

Set the FORGE_CURRENCY_SYMBOL environment variable to your desired symbol (e.g., export FORGE_CURRENCY_SYMBOL="€"). This overrides the default "$" value and applies immediately to new prompt renderings without requiring shell restarts.

Why is my cost showing as $0.00 even though I set a conversion rate?

The conversion rate multiplies the raw USD cost; if the base cost is very small (e.g., $0.0001), multiplying by typical conversion rates may still result in a value below 0.005, which rounds to 0.00 when formatted to two decimal places. Ensure your provider returns granular cost data or adjust expectations for very low-cost operations.

Does disabling Nerd Fonts affect the currency display?

No. The NERD_FONT and USE_NERD_FONT environment variables only control agent and model icons. The currency symbol from FORGE_CURRENCY_SYMBOL and cost formatting remain fully functional regardless of Nerd Font settings.

Where does the raw cost value originate before conversion?

The raw cost comes from the active conversation session data populated by the Forge engine when processing LLM requests. The ZshRPrompt struct receives this value through its cost field, then applies the conversion ratio and symbol formatting before displaying it in your terminal's right prompt.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}