promptfoo/site/docs/providers/echo.md

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Echo

Echo Provider

The Echo Provider is a simple utility provider that returns the input prompt as the output. It's particularly useful for testing, debugging, and validating pre-generated outputs without making any external API calls.

Configuration

To use the Echo Provider, set the provider ID to echo in your configuration file:

providers:
  - echo
  # or
  - id: echo
    label: pass through provider

Response Format

The Echo Provider returns a complete ProviderResponse object with the following fields:

• output: The original input string
• cost: Always 0
• cached: Always false
• tokenUsage: Set to { total: 0, prompt: 0, completion: 0 }
• isRefusal: Always false
• metadata: Any additional metadata provided in the context

Usage

The Echo Provider requires no additional configuration and returns the input after performing any variable substitutions.

Example

providers:
  - echo
  - openai:chat:gpt-4.1-mini

prompts:
  - 'Summarize this: {{text}}'

tests:
  - vars:
      text: 'The quick brown fox jumps over the lazy dog.'
    assert:
      - type: contains
        value: 'quick brown fox'
      - type: similar
        value: '{{text}}'
        threshold: 0.75

In this example, the Echo Provider returns the exact input after variable substitution, while the OpenAI provider generates a summary.

Use Cases and Working with Pre-generated Outputs

The Echo Provider is useful for:

• Debugging and Testing Prompts: Ensure prompts and variable substitutions work correctly before using complex providers.

• Assertion and Pre-generated Output Evaluation: Test assertion logic on known inputs and validate pre-generated outputs without new API calls.

• Testing Transformations: Test how transformations affect the output without the variability of an LLM response.

• Mocking in Test Environments: Use as a drop-in replacement for other providers in test environments when you don't want to make actual API calls.