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Overview

Messages are the building blocks of PromptL prompts. They define the flow of conversations between the user, the assistant, and other entities like tools. Each message is associated with a role that determines its purpose in the conversation.

PromptL supports the following message roles:

• System: Sets the context and rules for the assistant.
• User: Represents user input in the conversation.
• Assistant: Captures assistant responses or provides context for the LLM’s output.
• Tool: Represents interactions with external tools or APIs.

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Roles

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System Messages

System messages provide high-level instructions and context for the assistant.

<system>
  You are a personal finance advisor. Provide actionable insights in a friendly tone.
</system>

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User Messages

User messages simulate user input in the conversation.

<user>
  How can I save more money each month?
</user>

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Assistant Messages

Assistant messages represent LLM responses or “fake” previous outputs to guide the conversation.

<user>
  What's your name?
</user>

<assistant>
  I’m BudgetBot, your personal finance assistant. How can I help you today?
</assistant>

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Tool Messages

Tool messages represent the output of external tools or APIs called by the assistant during the conversation. They require a unique id attribute to match the tool call.

<assistant>
  <tool-call id="123" name="get-weather" arguments={{ { location: "Barcelona" } }} />
</assistant>

<tool id="123">
  It's 17ºC in Barcelona.
</tool>

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Tags

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The <message> Tag

Messages can be defined using the <message> tag with a role attribute:

<message role="system">
  This is a system message.
</message>

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Shortcut Tags

For convenience, you can use specific tags for each role:

• <system>: Equivalent to <message role="system">.
• <user>: Equivalent to <message role="user">.
• <assistant>: Equivalent to <message role="assistant">.
• <tool>: Equivalent to <message role="tool">.

<system>
  You are a friendly chatbot.
</system>
<user>
  What’s the weather today in Barcelona?
</user>
<assistant>
  Let me check for you!
  <tool-call id="123" name="get-weather" arguments={{ { location: "Barcelona" } }} />
</assistant>
<tool id="123">
  23ºC, sunny.
</tool>

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Content Types

Messages can contain different types of content. By default, all plain text is considered text content, but you can specify other types using the <content> tag or its shorthand equivalents.

• Text (default): <content type="text"> or <content-text>.
• Image: <content type="image"> or <content-image>. Add the image URL or base64-encoded string – depending on your provider’s requirements – as the content inside the tag.
• File: <content type="file"> or <content-file>. Add the file URL or base64-encoded string – depending on your provider’s requirements – as the content inside the tag. Requires a MIME type mime attribute to specify the file type.
• Tool Call: <content type="tool-call"> or <tool-call>. Represents a tool invocation with attributes like id, name, and arguments (optional). Only allowed inside assistant messages.

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Examples

<user>
  Take a look at this image:
  <content-image>[image url]</content-image>

  And this PDF:
  <content-file mime="application/pdf">[file url]</content-file>
</user>

<assistant>
  <tool-call id="123" name="get-weather" arguments={{ { location: "Barcelona" } }} />
</assistant>

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Best Practices

• Use System Messages for Context: Define clear rules for the assistant to guide its behavior.
• Leverage User Messages for Dynamic Input: Use uncontrolled user variables inside user messages to define a clear difference authority between the user and the system rules.

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Advanced Examples

Here’s how multiple message roles and content types can work together:

<system>
  You are a helpful assistant for travel planning.
</system>

<user>
  Find me a good restaurant in {{ city }}.
</user>

<assistant>
  Let me check for you.
  <tool-call id="456" name="find-restaurant" arguments={{ { location: city } }} />
</assistant>

<tool id="456">
  The best-rated restaurant in {{ city }} is Gourmet Central.
</tool>