Configuration

The YAML configuration format runs each prompt through a series of example inputs (aka "test case") and checks if they meet requirements (aka "assertions").

Assertions are optional. Many people get value out of reviewing outputs manually, and the web UI helps facilitate this.

Example

Let's imagine we're building an app that does language translation. This config runs each prompt through GPT-3.5 and Gemini, substituting language and input variables:

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
tests:
  - vars:
      language: French
      input: Hello world
  - vars:
      language: German
      input: How's it going?

tip

For more information on setting up a prompt file, see input and output files.

Running promptfoo eval over this config will result in a matrix view that you can use to evaluate GPT vs Gemini.

Use assertions to validate output

Next, let's add an assertion. This automatically rejects any outputs that don't contain JSON:

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
tests:
  - vars:
      language: French
      input: Hello world
    assert:
      - type: contains-json
  - vars:
      language: German
      input: How's it going?

We can create additional tests. Let's add a couple other types of assertions. Use an array of assertions for a single test case to ensure all conditions are met.

In this example, the javascript assertion runs Javascript against the LLM output. The similar assertion checks for semantic similarity using embeddings:

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
tests:
  - vars:
      language: French
      input: Hello world
    assert:
      - type: contains-json
      - type: javascript
        value: output.toLowerCase().includes('bonjour')
  - vars:
      language: German
      input: How's it going?
    assert:
      - type: similar
        value: was geht
        threshold: 0.6   # cosine similarity

tip

To learn more about assertions, see docs on configuring expected outputs.

Import providers from separate files

The providers config property can point to a list of files. For example:

providers:
  - file://path/to/provider1.yaml
  - file://path/to/provider2.json

Where the provider file looks like this:

id: openai:gpt-4o-mini
label: Foo bar
config:
  temperature: 0.9

Import tests from separate files

The tests config property takes a list of paths to files or directories. For example:

prompts: file://prompts.txt
providers: openai:gpt-4o-mini

# Load & runs all test cases matching these filepaths
tests:
  # You can supply an exact filepath
  - file://tests/tests2.yaml

  # Or a glob (wildcard)
  - file://tests/*

  # Mix and match with actual test cases
  - vars:
      var1: foo
      var2: bar

A single string is also valid:

tests: tests/*

Or a list of paths:

tests:
  - 'tests/accuracy'
  - 'tests/creativity'
  - 'tests/hallucination'

tip

We also support CSV datasets from local file and Google Sheets.

Import vars from separate files

The vars property can point to a file or directory. For example:

tests:
  - vars: file://path/to/vars*.yaml

You can also load individual variables from file by using the file:// prefix. For example:

tests:
  - vars:
      var1: some value...
      var2: another value...
      var3: file://path/to/var3.txt

Javascript and Python variable files are supported. For example:

tests:
  - vars:
      context: file://fetch_from_vector_database.py

This is useful when testing vector databases like Pinecone, Chroma, Milvus, etc.

Javascript variables

To dynamically load a variable from a JavaScript file, use the file:// prefix in your YAML configuration, pointing to a JavaScript file that exports a function.

tests:
  - vars:
      context: file://path/to/dynamicVarGenerator.js

dynamicVarGenerator.js receives varName, prompt, and otherVars as arguments, which you can use to query a database or anything else based on test context:

module.exports = function (varName, prompt, otherVars) {
  // Example logic to return a value based on the varName
  if (varName === 'context') {
    return {
      output: `Processed ${otherVars.input} for prompt: ${prompt}`,
    };
  }
  return {
    output: 'default value',
  };

  // Handle potential errors
  // return { error: 'Error message' }
};

This JavaScript file processes input variables and returns a dynamic value based on the provided context.

Python variables

For Python, the approach is similar. Define a Python script that includes a get_var function to generate your variable's value. The function should accept var_name, prompt, and other_vars.

tests:
  - vars:
      context: file://fetch_dynamic_context.py

fetch_dynamic_context.py:

def get_var(var_name: str, prompt: str, other_vars: Dict[str, str]) -> Dict[str, str]:
    # NOTE: Must return a dictionary with an 'output' key or an 'error' key.
    # Example logic to dynamically generate variable content
    if var_name == 'context':
        return {
            'output': f"Context for {other_vars['input']} in prompt: {prompt}"
        }
    return {'output': 'default context'}

    # Handle potential errors
    # return { 'error': 'Error message' }

Avoiding repetition

Default test cases

Use defaultTest to set properties for all tests.

In this example, we use a llm-rubric assertion to ensure that the LLM does not refer to itself as an AI. This check applies to all test cases:

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
defaultTest:
  assert:
    - type: llm-rubric
      value: does not describe self as an AI, model, or chatbot
tests:
  - vars:
      language: French
      input: Hello world
    assert:
      - type: contains-json
      - type: javascript
        value: output.toLowerCase().includes('bonjour')
  - vars:
      language: German
      input: How's it going?
    assert:
      - type: similar
        value: was geht
        threshold: 0.6

You can also use defaultTest to override the model used for each test. This can be useful for model-graded evals:

defaultTest:
  options:
    provider: openai:gpt-4o-mini-0613

YAML references

promptfoo configurations support JSON schema references, which define reusable blocks.

Use the $ref key to re-use assertions without having to fully define them more than once. Here's an example:

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
tests:
  - vars:
      language: French
      input: Hello world
    assert:
      - $ref: '#/assertionTemplates/startsUpperCase'
  - vars:
      language: German
      input: How's it going?
    assert:
      - $ref: '#/assertionTemplates/noAIreference'
      - $ref: '#/assertionTemplates/startsUpperCase'

assertionTemplates:
    noAIreference:
      type: llm-rubric
      value: does not describe self as an AI, model, or chatbot
    startsUpperCase:
      type: javascript
      value: output[0] === output[0].toUpperCase()

info

tools and functions values in providers config are not dereferenced. This is because they are standalone JSON schemas that may contain their own internal references.

Multiple variables in a single test case

The vars map in the test also supports array values. If values are an array, the test case will run each combination of values.

For example:

prompts: file://prompts.txt
providers:
  - openai:gpt-4o-mini
  - openai:gpt-4
tests:
  - vars:
      language:
        - French
        - German
        - Spanish
      input:
        - 'Hello world'
        - 'Good morning'
        - 'How are you?'
    assert:
      - type: similar
        value: 'Hello world'
        threshold: 0.8

Evaluates each language x input combination:

Vars can also be imported from globbed filepaths. They are automatically expanded into an array. For example:

  - vars:
      language:
        - French
        - German
        - Spanish
      input: file://path/to/inputs/*.txt

Using nunjucks templates

Use Nunjucks templates to exert additional control over your prompt templates, including loops, conditionals, and more.

Manipulating objects

In the above examples, vars values are strings. But vars can be any JSON or YAML entity, including nested objects. You can manipulate these objects in the prompt, which are nunjucks templates:

promptfooconfig.yaml:

tests:
  - vars:
      user_profile:
        name: John Doe
        interests:
          - reading
          - gaming
          - hiking
      recent_activity:
        type: reading
        details:
          title: 'The Great Gatsby'
          author: 'F. Scott Fitzgerald'

prompt.txt:

User Profile:
- Name: {{ user_profile.name }}
- Interests: {{ user_profile.interests | join(', ') }}
- Recent Activity: {{ recent_activity.type }} on "{{ recent_activity.details.title }}" by {{ recent_activity.details.author }}

Based on the above user profile, generate a personalized reading recommendation list that includes books similar to "{{ recent_activity.details.title }}" and aligns with the user's interests.

Here's another example. Consider this test case, which lists a handful of user and assistant messages in an OpenAI-compatible format:

tests:
  - vars:
      previous_messages:
        - role: user
          content: hello world
        - role: assistant
          content: how are you?
        - role: user
          content: great, thanks

The corresponding prompt.txt file simply passes through the previous_messages object using the dump filter to convert the object to a JSON string:

{{ previous_messages | dump }}

Running promptfoo eval -p prompt.txt -c path_to.yaml will call the Chat Completion API with the following prompt:

[
  {
    "role": "user",
    "content": "hello world"
  },
  {
    "role": "assistant",
    "content": "how are you?"
  },
  {
    "role": "user",
    "content": "great, thanks"
  }
]

Escaping JSON strings

If the prompt is valid JSON, nunjucks variables are automatically escaped when they are included in strings:

tests:
  - vars:
      system_message: >
        This multiline "system message" with quotes...
        Is automatically escaped in JSON prompts!

{
  "role": "system",
  "content": "{{ system_message }}"
}

You can also manually escape the string using the nunjucks dump filter. This is necessary if your prompt is not valid JSON, for example if you are using nunjucks syntax:

{
  "role": {% if 'admin' in message %} "system" {% else %} "user" {% endif %},
  "content": {{ message | dump }}
}

Variable composition

Variables can reference other variables:

prompts:
  - 'Write a {{item}}'

tests:
  - vars:
      item: 'tweet about {{topic}}'
      topic: 'bananas'

  - vars:
      item: 'instagram about {{topic}}'
      topic: 'theoretical quantum physics in alternate dimensions'

Accessing environment variables

You can access environment variables in your templates using the env global:

tests:
  - vars:
      headline: 'Articles about {{ env.TOPIC }}'

Tools and Functions

promptfoo supports tool use and function calling with OpenAI and Anthropic models, as well as other provider-specific configurations like temperature and number of tokens. For more information on defining functions and tools, see the OpenAI provider docs and the Anthropic provider docs.

Transforming outputs

Transforms can be applied at both the provider level and in test cases. The order of application is:

Provider transforms (always applied first)
Default test transforms (if specified in defaultTest)
Individual test case transforms (overrides defaultTest transform if present)

Note that only one transform is applied at the test case level - either from defaultTest or the individual test case, not both.

The TestCase.options.transform field is a Javascript snippet that modifies the LLM output before it is run through the test assertions.

It is a function that takes a string output and a context object:

transformFn: (output: string, context: {
  prompt: {
    // ID of the prompt, if assigned
    id?: string;
    // Raw prompt as provided in the test case, without {{variable}} substitution.
    raw?: string;
    // Prompt as sent to the LLM API and assertions.
    display?: string;
  };
  vars?: Record<string, any>;
}) => void;

This is useful if you need to somehow transform or clean LLM output before running an eval.

For example:

# ...
tests:
  - vars:
      language: French
      body: Hello world
    options:
      transform: output.toUpperCase()
    # ...

Or multiline:

# ...
tests:
  - vars:
      language: French
      body: Hello world
    options:
      transform: |
        output = output.replace(context.vars.language, 'foo');
        const words = output.split(' ').filter(x => !!x);
        return JSON.stringify(words);
    # ...

It also works in assertions, which is useful for picking values out of JSON:

tests:
  - vars:
      # ...
    assert:
      - type: equals
        value: 'foo'
        transform: output.category # Select the 'category' key from output json

tip

Use defaultTest apply a transform option to every test case in your test suite.

Transforms from separate files

Transform functions can be executed from external JavaScript or Python files. You can optionally specify a function name to use.

For JavaScript:

defaultTest:
  options:
    transform: file://transform.js:customTransform

module.exports = {
  customTransform: (output, context) => {
    // context.vars, context.prompt
    return output.toUpperCase();
  },
};

For Python:

defaultTest:
  options:
    transform: file://transform.py

def get_transform(output, context):
    # context['vars'], context['prompt']
    return output.upper()

If no function name is specified for Python files, it defaults to get_transform. To use a custom Python function, specify it in the file path:

transform: file://transform.py:custom_python_transform

Transforming input variables

You can also transform input variables before they are used in prompts using the transformVars option. This feature is useful when you need to pre-process data or load content from external sources.

The transformVars function should return an object with the transformed variable names and values. These transformed variables are added to the vars object and can override existing keys. For example:

prompts:
  - 'Summarize the following text in {{topic_length}} words: {{file_content}}'

defaultTest:
  options:
    transformVars: |
      return {
        uppercase_topic: vars.topic.toUpperCase(),
        topic_length: vars.topic.length,
        file_content: fs.readFileSync(vars.file_path, 'utf-8')
      };

tests:
  - vars:
      topic: 'climate change'
      file_path: './data/climate_article.txt'
    assert:
      - type: contains
        value: '{{uppercase_topic}}'

Transform functions can also be specified within individual test cases.

tests:
  - vars:
      url: 'https://example.com/image.png'
    options:
      transformVars: |
        return { ...vars, image_markdown: `![image](${vars.url})` }

Input transforms from separate files

For more complex transformations, you can use external files for transformVars:

defaultTest:
  options:
    transformVars: file://transformVars.js:customTransformVars

const fs = require('fs');

module.exports = {
  customTransformVars: (vars, context) => {
    try {
      return {
        uppercase_topic: vars.topic.toUpperCase(),
        topic_length: vars.topic.length,
        file_content: fs.readFileSync(vars.file_path, 'utf-8'),
      };
    } catch (error) {
      console.error('Error in transformVars:', error);
      return {
        error: 'Failed to transform variables',
      };
    }
  },
};

You can also define transforms in python.

defaultTest:
  options:
    transformVars: file://transform_vars.py

import os

def get_transform(vars, context):
    with open(vars['file_path'], 'r') as file:
        file_content = file.read()

    return {
        'uppercase_topic': vars['topic'].upper(),
        'topic_length': len(vars['topic']),
        'file_content': file_content,
        'word_count': len(file_content.split())
    }

Config structure and organization

For detailed information on the config structure, see Configuration Reference.

If you have multiple sets of tests, it helps to split them into multiple config files. Use the --config or -c parameter to run each individual config:

promptfoo eval -c usecase1.yaml

and

promptfoo eval -c usecase2.yaml

You can run multiple configs at the same time, which will combine them into a single eval. For example:

promptfoo eval -c my_configs/*

promptfoo eval -c config1.yaml -c config2.yaml -c config3.yaml

Loading tests from CSV

YAML is nice, but some organizations maintain their LLM tests in spreadsheets for ease of collaboration. promptfoo supports a special CSV file format.

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
tests: file://tests.csv

promptfoo also has built-in ability to pull test cases from a Google Sheet. The easiest way to get started is to set the sheet visible to "anyone with the link". For example:

prompts:
  - file://prompt1.txt
  - file://prompt2.txt
providers:
  - openai:gpt-4o-mini
  - vertex:gemini-pro
tests: https://docs.google.com/spreadsheets/d/1eqFnv1vzkPvS7zG-mYsqNDwOzvSaiIAsKB3zKg9H18c/edit?usp=sharing

Here's a full example.

See Google Sheets integration for details on how to set up promptfoo to access a private spreadsheet.

Example​

Use assertions to validate output​

Import providers from separate files​

Import tests from separate files​

Import vars from separate files​

Javascript variables​

Python variables​

Avoiding repetition​

Default test cases​

YAML references​

Multiple variables in a single test case​

Using nunjucks templates​

Manipulating objects​

Escaping JSON strings​

Variable composition​

Accessing environment variables​

Tools and Functions​

Transforming outputs​

Transforms from separate files​

Transforming input variables​

Input transforms from separate files​

Config structure and organization​

Loading tests from CSV​