# Anatomy of a Model Request — Prompt & Context Engineering

Source: https://www.skillbyai.com/en/prompt-context-engineering/f-anatomy

> Name the parts so you can budget and test them separately.

## Six building blocks

A typical request has: (1) **system instructions** (role, rules, format); (2) **tool definitions** (names, descriptions, parameter schemas, which also cost tokens); (3) **examples** (few-shot demonstrations); (4) **conversation history**; (5) **retrieved or injected content** (documents, database rows, tool results); and (6) the **current user request**. Each block has a different owner, change rate and trust level: instructions are yours and stable, documents change per request, user input and tool output are **untrusted**. Treat them as separate components with their own budget, versioning and tests.

## The blocks at a glance

Owner, change rate and trust per block.

```text
block              owner        changes          trust
system rules       you          per release      trusted
tool definitions   you          per release      trusted
examples           you          per release / per request (selected)   trusted
history            users+model  every turn       mixed
documents/results  data, tools  every request    UNTRUSTED content
user request       user         every request    UNTRUSTED
```

## Count tool schemas too

Twenty verbose tool definitions can take thousands of tokens on every call; include only the tools the current step needs.

**Quiz:** Which block should be treated as untrusted?

- [ ] Your fixed examples
- [ ] Your own reviewed system rules
- [ ] Your tool definitions
- [x] Retrieved documents and tool results

*Answer:* Retrieved documents and tool results. Content from outside your code may contain anything, including instructions.