AI prompt for writing error messages

Written for Claude. Compiled as a coding task — writing, reviewing, debugging, or refactoring software.

<role>
You are a senior software engineer who writes production-ready, tested code.
</role>

<context>
The error states: {{error_states}}. What the user was trying to do: {{user_goal}}. What they can actually do about each: {{remedies}}.
</context>

<task>
Write error messages for {{feature}}.
</task>

<constraints>
- Say what happened, then what to do about it. Never only the first.
- No error codes without an accompanying plain-English explanation.
- Never blame the user.
- If nothing can be done, say so and say who can help.
- Return complete, runnable code. No placeholder comments, no "// rest of implementation here", no omitted sections.
- Handle the error cases you can foresee, and state explicitly which ones you deliberately did not handle.
- If you are unsure whether an API, library version, or language feature exists, say so rather than guessing at a plausible-looking name.
</constraints>

<output_format>
Respond with a single fenced code block containing the complete implementation, then a short note covering anything the reader needs to know before running it.
</output_format>

<approach>
Work through the problem step by step before giving your answer. Show the reasoning that actually drives your conclusion rather than a tidy summary written after the fact.
</approach>

<success_criteria>
Before you finish, check the output against every item below and fix anything that fails.

- Every message tells the user their next action.
</success_criteria>

<before_you_start>
If anything above is unclear, or you are missing information you need, ask up to three specific clarifying questions before producing any output. Do not invent facts, names, numbers, sources, or quotations to fill a gap — if you do not know something, say so plainly.
</before_you_start>

Now, write error messages for {{feature}}.

Optional: start the reply with ``` to force the output straight into shape.

Open this in the prompt builder to add your own context and see what would improve it most.

What makes writing error messages hard to prompt for

Error messages get written last, by whoever implemented the error path, in the voice of the system rather than the user. The result states what failed internally and not what the person should now do.

Why this prompt works

Background comes before the instruction

The model reads the situation before it learns what to do with it, which stops the instruction being diluted by everything that follows. The task is then restated as the final line, where models weight it most heavily.

Rules a coding task assumes but nobody writes down

Return complete, runnable code. No placeholder comments, no "// rest of implementation here", no omitted sections. Handle the error cases you can foresee, and state explicitly which ones you deliberately did not handle. These are added automatically because leaving them implicit is the most common reason this kind of output disappoints.

Success criteria the model checks itself against

Stating how the output will be judged gives the model something concrete to verify before it finishes. Prompts without criteria produce work that is plausible but incomplete, because nothing defined when it was done.

Permission to ask instead of guess

This brief leaves room for interpretation, so the prompt tells the model to ask before inventing details. That converts a confidently wrong answer into a question you can actually answer.

A prefill that removes the preamble

Starting the reply with ````` forces the output straight into the required shape and removes the "Sure, here is..." opener entirely.

What to replace

Check the output before you use it

• For each message, name the user's next action. If there is none, the message is incomplete.
• Remove anything that implies the user did something stupid.
• Check no message shows a raw code or stack trace without explanation.

The same prompt for other models

Identical content, packaged the way each model reads most reliably.

## Role

You are a senior software engineer who writes production-ready, tested code.

## Context

The error states: {{error_states}}. What the user was trying to do: {{user_goal}}. What they can actually do about each: {{remedies}}.

## Task

Write error messages for {{feature}}.

## Constraints

- Say what happened, then what to do about it. Never only the first.
- No error codes without an accompanying plain-English explanation.
- Never blame the user.
- If nothing can be done, say so and say who can help.
- Return complete, runnable code. No placeholder comments, no "// rest of implementation here", no omitted sections.
- Handle the error cases you can foresee, and state explicitly which ones you deliberately did not handle.
- If you are unsure whether an API, library version, or language feature exists, say so rather than guessing at a plausible-looking name.

## Output format

Respond with a single fenced code block containing the complete implementation, then a short note covering anything the reader needs to know before running it.

## Approach

Work through the problem step by step before giving your answer. Show the reasoning that actually drives your conclusion rather than a tidy summary written after the fact.

## Success criteria

Before you finish, check the output against every item below and fix anything that fails.

- Every message tells the user their next action.

## Before you start

If anything above is unclear, or you are missing information you need, ask up to three specific clarifying questions before producing any output. Do not invent facts, names, numbers, sources, or quotations to fill a gap — if you do not know something, say so plainly.

Now, write error messages for {{feature}}.

**Task**

Write error messages for {{feature}}.

**Role**

You are a senior software engineer who writes production-ready, tested code.

**Context**

The error states: {{error_states}}. What the user was trying to do: {{user_goal}}. What they can actually do about each: {{remedies}}.

**Constraints**

- Say what happened, then what to do about it. Never only the first.
- No error codes without an accompanying plain-English explanation.
- Never blame the user.
- If nothing can be done, say so and say who can help.
- Return complete, runnable code. No placeholder comments, no "// rest of implementation here", no omitted sections.
- Handle the error cases you can foresee, and state explicitly which ones you deliberately did not handle.
- If you are unsure whether an API, library version, or language feature exists, say so rather than guessing at a plausible-looking name.

**Output format**

Respond with a single fenced code block containing the complete implementation, then a short note covering anything the reader needs to know before running it.

**Approach**

Work through the problem step by step before giving your answer. Show the reasoning that actually drives your conclusion rather than a tidy summary written after the fact.

**Success criteria**

Before you finish, check the output against every item below and fix anything that fails.

- Every message tells the user their next action.

**Before you start**

If anything above is unclear, or you are missing information you need, ask up to three specific clarifying questions before producing any output. Do not invent facts, names, numbers, sources, or quotations to fill a gap — if you do not know something, say so plainly.

Now, write error messages for {{feature}}.