Template Overrides

When a PromptTemplate is configured on an agent, you can update its default variables in-place without re-rendering. Call updatePromptVariables on the agent or template to merge new values — matching keys are overwritten, the rest are kept. The next agent call picks up the new values automatically.

import { createAgent, createPromptTemplate } from "@comma-agents/core";

const agent = createAgent({
  name: "reviewer",
  model: "openai/gpt-4o",
  systemPrompt: createPromptTemplate({
    template: "You are {{ role }}, reviewing {{ language }} code.",
    variables: { role: "a senior engineer" },
  }),
});

// Update variables on the agent — no render() call needed.
agent.updatePromptVariables({ language: "TypeScript" });

// The next call renders with the merged defaults:
// "You are a senior engineer, reviewing TypeScript code."

Updating templates directly

You can also update variables directly on the template — useful when the template is shared across multiple agents or before it is assigned:

const tpl = createPromptTemplate({
  template: "You are {{ role }}.",
  variables: { role: "an assistant" },
});

tpl.updatePromptVariables({ role: "a reviewer" });
await tpl.render(); // "You are a reviewer."

Adding new variables

This is a merge operation, so you can add new variables that did not exist at creation time:

tpl.updatePromptVariables({ name: "World" });
await tpl.render({ role: "a greeter" });
// Uses overridden "role" + newly added "name" from defaults.

How it works

When systemPrompt is a PromptTemplate, the agent stores a reference to it. Calling agent.updatePromptVariables(...) forwards to template.updatePromptVariables(...), which merges into the template's defaults via Object.assign. Since the template is shared by reference, any future call to agent.call() or template.render() uses the updated defaults.

If the agent was created with a static string systemPrompt, calling agent.updatePromptVariables() is a no-op — there is no template to update.

Related

• Prompts & Templates — overview and createPromptTemplate.
• Template Syntax — LiquidJS syntax and custom filters.
• In Description Files — using templates in YAML/JSON agent definitions.