Sentiment analysis: definition, methods, and applications

Malak Lahrach
Glossary
- 8 min reading
Published on
January 7, 2026

"Terrible service, I've been waiting for 3 days!" vs. "Thank you very much, problem solved quickly." You can see the difference at a glance. But when you have thousands of messages a day, how can you automatically detect dissatisfied customers?

That's wheresentiment analysis comes in. In this guide, find out what it is, how it works, and how to use it in your customer service department.

Sentiment analysis: definition

Sentiment analysis is an artificial intelligence technique that automatically identifies the emotional tone of a text: positive, negative, or neutral.

It is an application of NLP (Natural Language Processing) that goes beyond simply understanding content to capture the emotion behind it.

Sentiment analysis answers the question: How does this person feel?

Sentiment analysis levels

Binary analysis

The simplest form: positive or negative. Useful for a quick initial sorting.

Ternary analysis

Positive, negative, or neutral. Neutral allows you to distinguish factual messages without any particular emotion.

Analysis with score

A continuous score (e.g., -1 to +1) that measures the intensity of the feeling. "Disappointed" ≠ "Furious."

Multi-emotion analysis

Beyond positive/negative: joy, sadness, anger, surprise, fear... More subtle but more complex to implement.

Analysis by aspect

Identify sentiment on different aspects of the same message: "The product is great (positive) but the delivery was terrible (negative)."

How sentiment analysis works

Lexical approach

A dictionary associates words with sentiment scores. "Excellent" = +2, "Terrible" = -2. The overall score is the sum of the word scores.

Advantages: simple, explainable, no training data required.

Limitations: does not handle context, irony, or negations ("not bad" = positive).

Machine Learning Approach

A model learns from annotated examples (texts + corresponding sentiments).

Advantages: adapts to your context, better management of nuances.

Limitations: requires labeled data for training.

Deep Learning/LLM Approach

Modern language models understand context, irony, and innuendo.

Advantages: high performance, handles complex cases.

Limitations: more resource-intensive.

Sentiment analysis in customer service

1. Ticket prioritization

A ticket with a very negative sentiment must be handled as a priority. Automatic analysis makes it possible to detect emotional emergencies.

2. Real-time alerts

Immediate notification when a VIP customer or public message expresses strong negative sentiment.

3. Intelligent routing

Highly negative messages can be routed to experienced agents or managers.

4. Monitoring overall satisfaction

Track changes in average sentiment over time: are customers becoming more satisfied or dissatisfied?

5. Post-interaction analysis

Assess sentiment at the beginning vs. the end of the conversation: did the agent succeed in improving the customer's mood?

6. Detection of churn risks

A customer with consistently negative feelings is a candidate for leaving. Analysis allows you to intervene before they leave.

Klark integrates sentiment analysis to automatically detect dissatisfied customers and prioritize the most sensitive requests.

The challenges of sentiment analysis

Irony and sarcasm

"Well done, 10 days to deliver a package, that's really great!" The words are positive, but the sentiment is negative. Difficult to detect automatically.

The context

"That's crazy" can be positive (admiring) or negative (dismayed) depending on the context.

Informal language

Abbreviations, emojis, spelling mistakes... The language customers actually use is far removed from academic language.

Multilingualism

Every language has its own expressions and emotional register. A French model does not work as such in English.

Mixed messages

The same message can contain both positive and negative elements. An overall analysis may mask this nuance.

Implement sentiment analysis

1. Define your goal

Real-time prioritization? Comprehensive trend analysis? The use case guides the choice of tool.

2. Choose your approach

  • Ready-to-use API: quick to deploy, works well on generic text
  • Custom model: more work, but tailored to your vocabulary and context

3. Test on your data

Take a sample of tickets, analyze them manually, compare with the model's predictions.

4. Set action thresholds

At what score do you trigger an alert? Specific routing? Escalation?

5. Integrate into your workflows

Sentiment analysis is most valuable when integrated into your tools (CRM, help desk).

6. Measure and adjust

Check the accuracy regularly and adjust if necessary.

Sentiment analysis and KPIs

Sentiment analysis can complement or enrich your traditional indicators:

Classic KPIEmotional enrichment
CSATConfirm/contradict the reported score by analyzing the verbatim
NPSAnalyze the "why" behind the grade
Resolution rateIs the ticket really resolved if the sentiment remains negative?

Mistakes to avoid

Mistake #1: Trusting blindly

No model is perfect. Regularly check classifications on samples.

Mistake #2: Ignoring the business context

"Urgent" is not negative, but may require priority action. Adapt to your context.

Mistake #3: Analyzing without taking action

Detecting dissatisfaction without a response process is useless.

Mistake #4: Replacing CSAT with sentiment

These are complementary metrics, not substitutes. Sentiment is automatic but less reliable than explicit feedback.

Mistake #5: Neglecting privacy

Sentiment analysis processes personal data. Ensure you are GDPR compliant.

Sentiment analysis tools

Generic APIs

  • Google Cloud Natural Language
  • AWS Comprehend
  • Microsoft Azure Text Analytics
  • MonkeyLearn

Integrated into support tools

Zendesk, Freshdesk, and others now include native sentiment analysis.

Specialized solutions

Tools such as Klark analyze sentiment in the specific context of customer service, with greater relevance.

Frequently Asked Questions

Is sentiment analysis reliable?

Good models achieve 80-90% accuracy on plain text. They are less reliable when it comes to irony, sarcasm, or ambiguous messages.

Can we analyze the sentiment of phone calls?

Yes, through transcription (speech-to-text) and then text analysis. Some tools also analyze the tone of voice.

Does sentiment analysis replace surveys?

No, it complements them. Sentiment analysis is automatic and comprehensive, while surveys provide more structured but partial feedback.

Should there be one template per language?

Multilingual models exist and work well, but a model dedicated to your primary language will be more accurate.

Conclusion

Sentiment analysis is a powerful tool for understanding the emotional state of your customers on a large scale. It allows you to prioritize, alert, and act before dissatisfaction turns into attrition.

The keys to effective sentiment analysis:

  • Clearly define your use case
  • Test on your real data
  • Integrate into your existing workflows
  • Define concrete actions by sentiment level
  • Check accuracy regularly

Want to automatically detect your dissatisfied customers? Discover how Klark can help you.

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