📑 Table des matières

Prompt debugging : quand l IA ne comprend pas ce que vous voulez

Prompting 🟡 Intermédiaire ⏱️ 13 min de lecture 📅 2026-02-24

You've carefully written your prompt, pressed Enter… and the AI's response is off the mark. Too vague, off-topic, factually incorrect, or poorly formatted. It happens to everyone, even experts. The good news is that prompt debugging is a skill that can be learned. This guide provides a systematic methodology to diagnose and correct the bad responses of Claude and other LLMs.

🔍 Why AI "doesn't understand"

Before correcting, let's understand why things go wrong. LLMs don't actually "understand" your instructions — they predict the most likely continuation. When the result is bad, it's almost always due to one of these causes:

The 7 main causes of bad responses

# Cause Symptom Frequency
1 Ambiguity AI interprets differently than you Very frequent
2 Insufficient context Generic response, out of context Very frequent
3 Contradictory instructions Inconsistent or partial response Frequent
4 Task too complex Response that mixes everything Frequent
5 Hallucination Invented facts Moderate
6 Model bias "Politically correct" or generic response Moderate
7 Knowledge limitation Outdated or non-existent information Occasional

🩺 The 5-step diagnostic method

Step 1: Identify the type of problem

Before modifying your prompt, classify the problem:

The response is...

□ Too vague/generic → CONTEXT problem
□ Off-topic → FOCUS problem
□ Factually incorrect → HALLUCINATION problem
□ Poorly formatted → FORMAT problem
□ Too long/short → CONSTRAINTS problem
□ Good but not exactly what I wanted → PRECISION problem
□ Inconsistent → CONTRADICTORY INSTRUCTIONS problem

Step 2: Read your prompt as a stranger

Read your prompt from the perspective of someone who knows nothing about your context. Every ambiguous term, every implicit assumption is a potential source of error.

 Ambiguous prompt:
"Give me a summary of the report"

Questions a stranger would ask:
- Which report?
- Summary of what length?
- For which audience?
- What level of detail?
- Focus on which sections?

Step 3: Isolate the problematic variable

If your prompt is long, test it piece by piece. Remove sections one by one to identify the one causing the problem.

Original (problematic) prompt:
"You are a marketing expert. Analyze this campaign and propose
improvements. Be creative but stay within budget. 
Also think about SEO impact. Don't forget mobile."

Test 1 — Just the analysis:
"You are a marketing expert. Analyze this campaign: 
strengths, weaknesses, key metrics."

Test 2 — Just the improvements:
"Here's the campaign analysis: [result of test 1]
Propose 5 concrete improvements with estimated budget."

→ If test 1 works but not test 2: the problem 
   is in the improvement request, not in the analysis.

Step 4: Apply the appropriate correction

Depending on the type of problem identified, apply the corresponding correction (see following sections).

Step 5: Document and capitalize

Note what worked and what didn't. Build your "debugging journal" — this is how you'll become an expert.

🔧 Reformulation techniques

Technique 1: Progressive specification

Start with a simple prompt and add precision at each iteration.

# V1  Too vague
"Write an article about cloud computing" Result: generic Wikipedia article

# V2  Add context
"Write an article about cloud computing for 
French SME executives who are non-technical"
→ Result: better but still too theoretical

# V3 — Add structure
"Write an 800-word article about cloud computing.
Audience: French SME executives who are non-technical.
Angle: concrete savings achievable by migrating 
to the cloud. Include 3 quantified case studies."
→ Result: much better but format not ideal

# V4 — Add format ✅
"Write an 800-word article about cloud computing.
Audience: French SME executives who are non-technical.
Angle: concrete savings achievable by migrating 
to the cloud.

Structure:
- Catchy title with a number
- Intro: the problem (exploding IT costs)
- 3 sections: each a real case with before/after quantified
- Conclusion: checklist to get started
- Tone: professional but accessible, no jargon"
→ Result: ✅

Technique 2: Inversion (asking what you DON'T want)

Sometimes, saying what you don't want is more effective than saying what you want.

 "Write a professional email"
 Result often too formal, clichéd

 "Write a professional email.

DO NOT include:
- 'I take the liberty of contacting you'
- 'Feel free to get back to me'  
- 'Best regards' (use 'See you soon' or 'Have a good day')
- Sentences longer than 20 words
- More than 5 lines total

The tone should be direct, human, like a message between 
colleagues who respect each other."

Technique 3: Negative example

Show the model a bad example and ask it to do the opposite.

"Here's a bad follow-up email:

'Dear Sir, I am writing to follow up on my 
previous email which remained unanswered. As I mentioned,
our solution could interest you. I remain at your 
disposal for any further information. Best regards.'

Problems: passive-aggressive, vague, no added value,
language clichés.

Write a better version that:
- Brings new useful information
- Creates urgency naturally
- Is max 4 lines
- Has a clear CTA"

Technique 4: Meta prompt

Ask the AI to help you write a better prompt.

"I want to get [DESIRED RESULT] but my prompts 
give poor results. Here's my current prompt:

[YOUR PROMPT]

And here's the type of response I get:
[EXAMPLE OF BAD RESPONSE]

What I really want:
[DESCRIPTION OF IDEAL RESULT]

Rewrite my prompt to get better results.
Explain what you changed and why."

Technique 5: Prompt chaining

If a single prompt gives poor results, break the task into several steps.

 Single prompt for everything:
"Analyze this dataset, identify trends, 
propose actions and write a 2-page report"

✅ Prompt chain:
Prompt 1: "Analyze this dataset. List the 5 
most important observations with numbers."

Prompt 2: "Based on these observations: [result 1]
Identify the 3 main trends and their causes."

Prompt 3: "Based on these trends: [result 2]
Propose 5 concrete actions with estimated impact and priority."

Prompt 4: "Summarize the following elements into a structured 
2-page report: [results 1+2+3]"

OpenClaw automates this chaining process, making prompt debugging much easier as you can identify exactly which step is problematic.

🎯 Solving specific problems

Problem: Too generic responses

Diagnosis: Lack of context and specificity

BEFORE:
"Give me some marketing advice"

AFTER:
"You advise a French B2B SaaS startup (accounting tool, 
18 months old, 50 clients, ARR 80K€, 
2 people in marketing, budget 3K€/month).

Give 5 marketing actions to do this month, sorted by 
impact/effort. For each action: what, how, target KPI."

Problem: Hallucinations (invented facts)

Diagnosis: The model invents when it doesn't know

Possible corrections:
1. Add: "If you're not sure of a fact, say so 
   explicitly. Prefer saying 'I don't know' rather than inventing."

2. Ask for sources: "For each factual statement,
   indicate if it's a verified fact, an estimate, or a 
   guess."

3. Limit the scope: "Base your response ONLY on the 
   information I provide. Don't supplement with external 
   knowledge."

4. Cross-check: test the same prompt on 
   [OpenRouter](/out?id=6) with multiple models. If responses diverge on a fact, it's probably invented.

Problem: Incorrect output format

Diagnosis: Insufficient or ambiguous format instructions

BEFORE: 
"Present the results in a table"
 The model creates a poorly structured table

AFTER:
"Present the results in a Markdown table with 
exactly these columns:
| Criterion | Score (/10) | Comment (1 sentence) | Priority |

Sort by decreasing score. Add a 'AVERAGE' row 
at the end. Use emojis for priority: 
🔴 high, 🟡 medium, 🟢 low."

Problem: Inappropriate tone

Diagnosis: The model doesn't capture the desired register

Technique: Provide a sample of your tone

"Write in THIS tone (example of my style):

'Let's be honest: 90% of SaaS landing pages 
look the same. Same hero, same 'Trusted by 1000+ companies',
same blue CTA. And that's exactly why yours 
doesn't convert.'

Now write an introductory paragraph about 
SaaS pricing mistakes in the same style."

Problem: Response that ignores constraints

Diagnosis: Too many constraints buried in the text

BEFORE (constraints buried) :
"Write a 500-word article about SEO, in French,
with concrete examples, for beginners, with an 
accessible tone, no technical jargon, and include a 
comparative table of tools."

AFTER (structured constraints) :
"Write an article about SEO.

MANDATORY CONSTRAINTS:
- Length: 500 words (±50)
- Language: French
- Audience: complete beginners
- Tone: accessible, conversational
- Jargon: forbidden (explain each technical term)

REQUIRED CONTENT:
- 3 concrete examples
- 1 comparative table of tools (3-5 tools)
- 1 actionable checklist in conclusion"

📊 Quick diagnostic matrix

Symptom Probable cause Correction
Too generic Missing context Add who, what, for whom, constraints
Off-topic Ambiguous prompt Reformulate + add "DO NOT talk about..."
Too long No length constraint Specify: "in X words/phrases/points"
Too short Not enough details requested Add "develop each point with..."
Poorly formatted Format not specified Provide exact template to follow
Hallucination No safeguard "Say when you're not sure"
Inconsistent Contradictory instructions Reread and remove contradictions
Wrong tone Tone not exemplified Provide sample of desired tone
Incomplete Task too broad Break down into sub-tasks (prompt chaining)

🔄 Iterative debugging workflow

Here's the complete process that pros follow:

1. SEND initial prompt
     
2. EVALUATE response (0-10)
     
   Score  8 ?   Done, save prompt
      No
3. DIAGNOSE (what type of problem?)
     
4. HYPOTHESIS (what's the probable cause?)
     
5. CORRECTION (apply appropriate technique)
     
6. RE-TEST (same question, modified prompt)
     
   Back to step 2

Maximum 5 iterations. If after 5 attempts the result 
isn't satisfactory:
 Change approach completely
 Break down task
 Test another model via OpenRouter

🛠️ Tools for debugging

Testing on multiple models

Use OpenRouter to submit the same prompt to different models. If Claude gives a good response but GPT-4 doesn't (or vice versa), the problem comes from the prompt, not the model.

| Model | Strength | Weakness |
|--