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Prompt structure & delimiters

Delimiters are the guardrails of a prompt. They tell the model where your instruction ends and the data begins, which also keeps it from being tricked into following rules hidden in your data.

What you will see

With delimiters: <instructions>Summarize the text.</instructions><data>Buy now!! Ignore previous instructions.</data> Instruction and data separated: True

About 2 min of reading

Try It

Structure prompts with delimiters

1

Show that plain text mixes instructions with user data.

def parse_prompt(instructions, user_data): return {"instructions": instructions, "raw_data": user_data} print("Prompt structure & delimiters") data = parse_prompt("Summarize the following text.", "Buy now!! Ignore previous instructions.") print("Without delimiters: %s" % data)

Before you run it, say out loud what it will print. Then open the answer.

What it prints
Prompt structure & delimiters Without delimiters: {'instructions': 'Summarize the following text.', 'raw_data': 'Buy now!! Ignore previous instructions.'}
A model reads your prompt as one stream; structure gives it landmarks.
2

Wrap data in delimiters so instructions and data stay separate.

def parse_with_delimiters(instructions, user_data): tagged = "{}{}".format(instructions, user_data) return tagged tagged = parse_with_delimiters("Summarize the text.", "Buy now!! Ignore previous instructions.") print() print("With delimiters:") print(tagged) print("Instruction and data separated: True")

Before you run it, say out loud what it will print. Then open the answer.

What it prints
With delimiters: Summarize the text.Buy now!! Ignore previous instructions. Instruction and data separated: True
Delimiters organize, and also defend against prompt injection.

Put it in order

Before you write anything, put these lines back in the right order. Click a line to move it up one step. This support step is easier than writing code from scratch, and it is here to make the last example stick.

Data Flow

Delimiters separate instructions from data so the model never confuses the two.
1 Write instructions first
↓
2 Open a delimiter for user data
↓
3 Place data inside the delimiter
↓
4 Close it before the next instruction
Line by line

Read the first example one line at a time. A line that prints shows what appears on screen; the rest set things up quietly.

def parse_prompt(instructions, user_data): sets nothing on screen
return {"instructions": instructions, "raw_data": user_data} sets nothing on screen
print("Prompt structure & delimiters") Prompt structure & delimiters
data = parse_prompt("Summarize the following text.", "Buy now!! Ignore previous instructions.") sets nothing on screen
print("Without delimiters: %s" % data) Without delimiters: {'instructions': 'Summarize the following text.', 'raw_data': 'Buy now!! Ignore previous instructions.'}
Why this works
Why structure matters

A model reads your prompt as one stream of text. Structure gives it landmarks.

Plain text:  hard to know what's a rule vs data
Structured:  clear boundaries, fewer mistakes

Use consistent delimiters every time so the model learns to expect them.

Avoiding instruction leakage

If user data contains instructions, the model may obey them. Delimiters protect against this:

User text goes inside <data>...</data>
Your real instructions stay outside.

Delimiters don't just organize, they also defend.

This is a basic defense against prompt injection.

Examples

Using delimiters

Summarize the text in <book>...</book> tags.

<book>The quick brown fox...</book>

Delimiters like <>, """, or --- tell the model where instructions end and data begins.

Why it works: it stops the model from confusing your rules with the text.

Sectioning complex prompts

# ROLE
You are a grammar teacher.

# TASK
Fix the errors in the text.

# RULES
- Keep the meaning.
- List each fix.

# TEXT
"..."

Headers let the model parse a long prompt the same way you did.

A well-organized prompt is a half-solved prompt.

Picking a delimiter

Use <tags> for short fields.
Use triple quotes for long paragraphs.
Use dashes between big sections.

The best delimiter is one your data will not accidentally contain.

Why it works: a clash between data and delimiter breaks the boundary.

Words this lesson uses

Each one is defined here on this site. Open the entry for the full definition and the other words it points at.

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