Reference Cards in System Prompts: A Reusable Template

Many of our system prompts follow a "reference card" pattern: a small, structured block at the top that anchors the model to a known set of facts. This post is the template.

The template

## Reference\n- Source: <URL>\n- Version: <YYYY-MM-DD>\n- Format: TOON (fallback: JSON)\n\n<toon table here>\n

Why these fields

• Source: anchors the model to a maintainer. Models deprioritize anonymous facts.
• Version: scopes the snapshot. If the model has stale knowledge, this gives it a hint.
• Format: helps you debug. If a model struggles with TOON, the note tells you to try JSON.

Common variants

• Add a Use line that says what the model should do with the card. Useful for ambiguous references.
• Add a Do not line for negative constraints ("do not invent codes not in this table").

What it costs

Three short lines, ~40 tokens. For most agents, the cheapest quality boost available.