Prompt Templates

Inside prompt: (and system:) you get a small, type-checked template language. Every reference is validated against the agent's typed inputs, with located file:line:col diagnostics.

At a glance

Construct	Example
Interpolation	{inputs.topic}
Environment	{env.API_BASE}
Object fields	{inputs.user.name}
Loops	{#each inputs.items as x, i}{i}. {x}{/each}
Empty fallback	{#each xs as x}…{:else}none{/each}
Destructuring	{#each rows as {title, score}}…{/each}
Conditionals	{#if inputs.verbose}…{:else if inputs.brief}…{:else}…{/if}
Literal braces	{{ and }}

Interpolation

{inputs.<name>} inserts a declared input and {env.<NAME>} inserts an environment variable (process.env.<NAME>, empty string if unset). {{ and }} are literal braces.

Objects render as TOON

When an interpolated value is an object or array, the compiler emits toonValue(...) so it renders as compact TOON in the prompt — not [object Object]. Scalars stay byte-identical to plain ${...}.

Loops

Iterate an array input with {#each inputs.<name> as <item>} … {/each}. Add a 0-based index with {#each … as <item>, <i>}, an empty-list fallback with {:else}, and destructure object elements with {#each rows as {a, b}}.

prompt: |
  Summarize these notes:
  {#each inputs.notes as note, i}
  {i}. {note}
  {:else}
  No notes provided.
  {/each}

Loops compile to .map().join("") in the emitted TypeScript.

Conditionals

Include a section based on a boolean input with {#if inputs.<flag>} … {:else if inputs.<other>} … {:else} … {/if} (a leading ! negates).

prompt: |
  {#if inputs.detailed}
  Write a thorough analysis.
  {:else}
  Keep it brief.
  {/if}

Conditionals compile to nested ternaries — all validated against the typed inputs.

Everything together

agent: brief
model: claude-opus-4-7
description: Summarize sources for an audience, optionally in detail.
inputs[3]{name,type}:
  sources,"{title:string;url:string}[]"
  detailed,boolean
  audience,string
prompt: |
  Write a brief for {inputs.audience}.
  {#each inputs.sources as {title, url}, i}
  {i}. {title} — {url}
  {:else}
  No sources provided.
  {/each}
  {#if inputs.detailed}
  Include a thorough analysis section.
  {:else}
  Keep it to a single paragraph.
  {/if}
outputs[1]{name,type}:
  brief,string

Open this in the playground →