Optimizing Prompts for Text Classification in Amazon Bedrock: From Manual to Automatic Approaches

Text classification is a crucial task in many organizations, allowing businesses to efficiently process and organize textual data at scale. While traditional machine learning approaches required significant data science expertise, large language models (LLMs) now provide a more accessible approach through prompt engineering. In this blog post, we'll explore various strategies to optimize prompts for text classification tasks, including Amazon Bedrock's automated prompt optimization feature.

Business Use Cases for Text Classification

Text classification applies to various business scenarios:

Document Classification: Organizations deal with vast amounts of documents that need to be categorized by type (contracts, invoices, reports), department (legal, finance, marketing), or priority level. Proper classification enables efficient storage, retrieval, and workflow automation.
Customer Support Triage: Customer inquiries arriving via email, chat, or web forms need to be classified by issue type (technical, billing, account access) and urgency to route them to the appropriate support team and prioritize resolution.
Content Moderation: Online platforms must classify user-generated content to identify and filter inappropriate material, detect policy violations, and ensure community guidelines are maintained.
Compliance Monitoring: In regulated industries, communications need to be classified to identify potential compliance risks, such as disclosure of sensitive information or improper financial advice.

Traditional ML vs. Generative AI Approach

Traditionally, implementing text classification required collecting and labeling large datasets, often numbering in the thousands or tens of thousands of examples. The process demanded extensive feature engineering to transform raw text into meaningful numerical representations. Data scientists needed to select and tune appropriate algorithms, requiring deep NLP expertise and specialized knowledge. These projects typically involved significant time investments for model development and validation, often taking weeks or months to move from concept to production.

With generative AI and foundation models, we now have access to a more streamlined approach. We can achieve impressive results through prompt engineering, leveraging the knowledge already embedded in these models. While we still need labeled data for evaluation and fine-tuning, the amount required is substantially less than traditional methods, as foundation models can generalize effectively from fewer examples. Development cycles are dramatically shortened, allowing teams to create working prototypes in hours rather than weeks. Additionally, these solutions can be deployed without extensive ML infrastructure, making advanced text classification accessible to organizations without dedicated data science teams.

The Challenge of High-Quality Classification

Despite the accessibility of LLMs, achieving high-quality text classification results still presents challenges:

Many business classification tasks require domain-specific knowledge beyond general language understanding
Real-world applications often involve many classification labels that aren't always mutually exclusive
Edge cases and ambiguous inputs can lead to inconsistent results
Business requirements may evolve, requiring an adaptive framework

To achieve reliable, high-quality classifications, we need:

A well-defined set of classification labels with clear criteria
Ground truth data with examples representing different scenarios
A robust evaluation framework to measure performance
An iterative approach to prompt optimization

Approaches to Prompt Optimization

Let's explore four approaches to optimize text classification prompts, from manual to fully automated.

1. Hand-Crafted Prompts with Best Practices

The most straightforward approach involves applying established prompt engineering techniques:

1
2
3
4
5
6
7
You are a document classification expert. Classify the following document into EXACTLY ONE of these categories:
- Invoice (contains billing details, amounts, payment terms)
- Contract (contains legal terms, signatures, binding language)
- Report (contains analysis, findings, recommendations)
- Email (contains correspondence between parties)
Respond ONLY with the category name.
Document: [DOCUMENT TEXT]

Best practices include:

Clear, specific instructions
Explicit classification criteria
Few-shot examples for complex cases
Consistent output format requirements
Task-specific context setting

While effective, this approach requires domain knowledge and multiple iterations of testing and refinement.

Further Reading:

Prompt Engineering Guidelines on the Amazon bedrock documentation
Prompting best practices for Amazon Nova understanding models
Amazon Bedrock Prompting GitHub repository

2. Meta-Prompt Approach

A more advanced technique uses "meta-prompts" - prompts that help generate better prompts:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
You are an expert in creating effective prompts for text classification.

I need a prompt that will help an LLM classify customer support tickets into these categories:
[Technical Issue, Billing Question, Account Access, Feature Request]

Some challenging examples include:
[EXAMPLES OF DIFFICULT CASES]

Create an optimized prompt that:
1. Achieves high classification accuracy
2. Handles ambiguous cases consistently
3. Works well across different writing styles
4. Properly distinguishes between similar categories

Your optimized prompt should include instructions and examples.

This approach leverages the LLM's own capabilities to improve prompt quality but still requires manual evaluation and refinement.

Additional Resources:

Anthropic Prompt Generator
Anthropic Meta-prompt notebook

3. Amazon Bedrock Prompt Optimization

Amazon Bedrock now offers an automatic prompt optimization feature that takes the guesswork out of prompt engineering. This service analyzes your prompt and rewrites it to improve inference results for your specific use case.

How it works:

You submit a prompt you want to optimize and select the model you want to optimize for. Amazon Bedrock then analyzes the prompt components and rewrites the prompt to improve performance. You can also compare the original and optimized prompts side-by-side.

Using Amazon Bedrock Prompt Optimization

In the console:

Write a prompt in an Amazon Bedrock playground or using Prompt management
Select a model for optimization
Click the optimization icon (wand symbol)
Review the analysis and optimized prompt
Choose to use the optimized prompt or keep your original

Via API:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
import boto3

# Set values
TARGET_MODEL_ID = "anthropic.claude-3-sonnet-20240229-v1:0"
PROMPT = "Classify this document as either an invoice, contract, or report: "

client = boto3.client('bedrock-agent-runtime')
response = client.optimize_prompt(
    input={"textPrompt": {"text": PROMPT}},
    targetModelId=TARGET_MODEL_ID
)

# Handle the response stream
for event in response['optimizedPrompt']:
    if 'optimizedPromptEvent' in event:
        print("OPTIMIZED PROMPT:", event['optimizedPromptEvent'])
    else:
        print("ANALYSIS:", event['analyzePromptEvent'])

At the time of writing the feature is in preview.

For further details, see the Amazon Bedrock's documentation.

4. Algorithmic Prompt Optimization

For the most sophisticated approach, we can examine OPRO (arXiv:2309.03409 [cs.LG]), Optimization by PROmpting methodology, which uses LLMs as optimizers in an iterative process.

How OPRO works for prompt optimization

Meta-Prompt Construction: Create a prompt containing:
- Previously tested prompts with their performance scores
- Task description and evaluation criteria
- Example inputs and outputs for the classification task
Solution Generation: The LLM generates multiple candidate prompts
Evaluation: Each prompt is tested on a validation set to measure performance
Feedback Loop: The best-performing prompts and their scores are incorporated into the meta-prompt for the next iteration
Iteration: Steps 2-4 are repeated, with each cycle potentially producing better prompts

Here is an example OPRO meta-prompt template for text classification (code sample below):

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
meta_prompt = f"""
        You are an AI assistant tasked with generating instructions for a text classification task.
        The goal is to classify text into one of these categories: {", ".join(ALLOWED_CATEGORIES)}.
        
        Here are some example texts with their correct categories:
        <examples>
        {generate_examples(dataset, NUM_EXAMPLES)}
        </examples>
        
        Previous instructions and their scores (higher is better):
        <previous_instructions>
        {format_instructions(best_instructions, best_scores)}
        </previous_instructions>
        
        Please generate 3 new instruction sets that could potentially achieve higher accuracy.
        Each instruction-set should be enclosed inside <inst></inst> tags.
        Leverage previous instructions and examples to enrich category descriptions and strive for better classification results.
        """

This approach can dramatically improve classification performance, sometimes outperforming human-designed prompts by significant margins. The technique leverages the LLM's pattern recognition capabilities to explore the prompt space intelligently.

Notes:

Cost: The heavy use of LLMs across iterations for prompt generation and testing has its associated costs, which can be assessed beforehand.
Overfitting: At some point the iterations may stop producing better scoring prompts and the process should be stopped. It is advisable to retain a final test data set with previously unseen examples to help ensure we are not overfitting.

Code Sample

This code sample walks through a simple implementation which leverages Amazon Bedrock LLMs, and applies the methodology to a text classification task for work candidate resume documents.

Implementing Your Text Classification Strategy

For developers looking to implement effective text classification with LLMs, I recommend this workflow:

Start simple: Begin with a basic hand-crafted prompt based on best practices
Leverage automation: Use Amazon Bedrock's prompt optimization to refine your initial prompt
Evaluate thoroughly: Test against a diverse set of inputs to identify edge cases
Iterate systematically: For critical applications, consider implementing an OPRO-like approach for continuous optimization
Monitor performance: Classification needs evolve over time, so establish regular evaluation cycles

Conclusion

Prompt optimization for text classification represents the intersection of art and science in the generative AI era. While traditional approaches required significant data science expertise, foundation models combined with effective prompt engineering now enable powerful classification capabilities with much less overhead.

Amazon Bedrock's prompt optimization feature provides a valuable middle ground between manual engineering and sophisticated algorithmic approaches. By leveraging these tools, developers can create high-performing text classification systems that deliver business value without requiring deep NLP expertise.

Have you tried Amazon Bedrock's prompt optimization feature for your text classification tasks? Share your experiences in the comments below!

Any opinions in this post are those of the individual author and may not reflect the opinions of AWS.

Select your cookie preferences

Site Terms, Privacy, and more.