Dynamic Variables

Use , , and other dynamic variables in prompts and workflows

Dynamic variables resolve at runtime — inject today’s date, timestamps, or custom values into agent prompts without hardcoding.

from praisonaiagents import Agent

agent = Agent(
    name="Researcher",
    instructions="You research news. Today is {{today}}.",
)
agent.start("Find AI news for {{today}}")

The user sends a prompt with {{today}} or custom placeholders; resolvers inject live values before the model runs.

How It Works

Quick Start

1. Use built-in variables in a prompt

   from praisonaiagents import Agent
   
   agent = Agent(
       name="Researcher",
       instructions="You research news. Today is {{today}}.",
   )
   
   agent.start("Find AI news for {{today}}")
   # Resolves to: "Find AI news for June 23, 2026"
   
2. Register a custom provider

   from praisonaiagents import Agent
   from praisonaiagents.utils import register_variable_provider
   
   register_variable_provider("author", lambda: "PraisonAI Team")
   
   agent = Agent(name="Writer", instructions="Articles by {{author}}")
   agent.start("Write a summary for {{today}}")
   

Built-in Variables

Variable	Example Output	Description
{{today}}	June 23, 2026	Human-readable date
{{date}}	2026-06-23	ISO date format
{{now}}	2026-06-23T11:00:00	ISO datetime
{{timestamp}}	1737280800	Unix timestamp
{{uuid}}	a1b2c3d4-…	Random UUID
{{year}}	2026	Current year
{{month}}	June	Current month name

Variables resolve in Agent.start(), Agent.run(), and workflow execution.

Common Patterns

Workflow YAML

framework: praisonai
topic: "Research AI developments for {{today}}"

roles:
  researcher:
    role: AI Researcher
    goal: "Find news for {{month}} {{year}}"
    tasks:
      research:
        description: "Research {{topic}}"
        expected_output: "Summary with sources"

Direct substitution

from praisonaiagents.utils import substitute_variables

text = substitute_variables("Hello {{today}}", {"topic": "AI"})

Dynamic variables are lazy-loaded — no performance impact when unused.

Best Practices

Prefer {{today}} over hardcoded dates

Prompts with {{today}} stay accurate across sessions without manual updates.

Register custom providers once at startup

Call register_variable_provider() before creating agents that reference custom variables.

Combine with static template variables

Pass static values via substitute_variables(text, {"topic": "AI"}) alongside built-in dynamic ones.

Use in workflow YAML

Workflow task descriptions and goals support the same {{today}}, {{year}}, and custom providers.

Related

Templates

System and prompt templates

Workflows

YAML workflows with variable substitution