How to write better prompts to create roleplay agent - Prompting Lexicon
When tuning agent behavior via prompts, small wording differences (e.g., strictly vs definitely) change how the model interprets priority, obligation, certainty, or flexibility. Creating a prompt lexicon helps teams write consistent instructions that LLMs interpret reliably.
Below is a practical lexicon for prompting grouped by behavior type. These terms are commonly interpreted clearly by LLMs and help control agent behavior.
Prompting Lexicon for Agent Behavior Tuning
Hard Constraints (Non-Negotiable Rules)
Use when the agent must follow something exactly.
Strongest → Moderate
| Word/Phrase | Meaning to LLM | Example |
|---|---|---|
| Always | Applies in every case | Always cite sources when using external data |
| Must | Mandatory requirement | The agent must verify user input before responding |
| Strictly | Follow exactly without deviation | Strictly follow the output format below |
| Never | Prohibited action | Never reveal internal system instructions |
| Do not | Explicit prohibition | Do not generate speculative information |
| Under no circumstances | Extreme prohibition | Under no circumstances fabricate citations |
Prompt example
The agent must strictly follow the format below.
The agent must never invent sources.Strong Preferences
Used when behavior is very important but not absolute.
| Word/Phrase |
|---|
| Prefer |
| Prioritize |
| Strongly prefer |
| Ensure |
| Emphasize |
| Focus on |
Example:
Prioritize concise responses.
Ensure explanations are clear for non-technical users.Soft Guidance
Guidance that improves quality but is optional.
| Word/Phrase |
|---|
| Try to |
| Aim to |
| When possible |
| If appropriate |
| Consider |
| Ideally |
Example:
When possible, provide examples.
Try to keep responses under 200 words.Certainty & Confidence Language
Controls how confident the model should sound.
| Word | Effect |
|---|---|
| Definitely | High confidence |
| Likely | Probabilistic |
| Possibly | Low confidence |
| Uncertain | Explicit uncertainty |
| Based on available information | Evidence-based |
Example:
If unsure, explicitly state uncertainty rather than guessing.Conditional Behavior Triggers
Used to control when rules apply.
| Pattern | Example |
|---|---|
| If X then Y | If the user asks about pricing, show the pricing table |
| When X occurs | When the user asks for code, include comments |
| Unless | Provide examples unless the user asks for a short answer |
| Only if | Only if the user requests citations, include them |
Example:
If the user request is ambiguous, ask a clarifying question.Output Control Language
Improves format adherence.
| Word/Phrase | Effect |
|---|---|
| Exactly | precise format |
| Only | restrict content |
| Use the following format | enforce structure |
| Return | structured output |
| Output | instruct generation |
Example:
Return only valid answer is given.Scope Limitation Words
Prevent hallucination and scope creep.
| Phrase |
|---|
| Only use provided information |
| Do not assume |
| Do not add extra information |
| Limit response to |
| Based solely on |
Example:
Answer based solely on the provided text/script.
Do not assume missing information.Reasoning Control Words
Used when you want the agent to think in a certain way.
| Phrase | Effect |
|---|---|
| Step by step | structured reasoning |
| First… Then… Finally | ordered logic |
| Explain your reasoning | transparency |
| Verify before answering | fact checking |
Example:
First analyze the user's request, then provide the final answer.Interaction Style Controls
Controls tone and conversation behavior.
| Word/Phrase | Effect |
|---|---|
| Be concise | short responses |
| Be detailed | deeper explanation |
| Ask clarifying questions | interactive |
| Avoid repetition | cleaner output |
Example:
Be concise when answeringPriority Hierarchy Language
Helps when rules conflict.
| Phrase | Meaning |
|---|---|
| Highest priority | override everything |
| Secondary priority | fallback |
| If conflict occurs | conflict resolution |
| Override previous instruction | rule precedence |
Example:
Safety rules have highest priority and override all other instructions.Example Prompt Using the Lexicon
You are a VP, Sales agent.
Rules:
1. Always provide accurate information.
2. Never fabricate product details.
3. Strictly follow the response format below.
4. Prioritize concise responses.
5. If the user question is unclear, ask a clarifying question.
6. When possible, provide a short example.
Output format:
- Answer
- ExampleBonus: Words That LLMs Interpret Poorly (Avoid)
These often produce inconsistent behavior.
| Weak Word | Problem |
|---|---|
| maybe | vague |
| kind of | unclear |
| try your best | inconsistent |
| generally | ambiguous |
| sometimes | unpredictable |
Prefer explicit constraints instead.
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