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Fill-in-the-Middle: AI Code Infilling (2D)

An interactive exploration of how AI models generate code snippets by predicting missing parts.

mysimulator teamUpdated June 2026≈ 3 min read▶ Open the simulation

What Fill-in-the-Middle Is

Fill-in-the-Middle (FIM) is a technique used to predict the missing parts of a code snippet. It involves an AI model analyzing the context around the missing section and generating probable completions based on learned patterns from vast datasets.

The FIM method helps in understanding how machine learning models process and generate text, particularly in programming languages, offering insights into their predictive capabilities.

How It Works

In the 2D multi-panel view of FIM, you can observe the source order of a code snippet alongside the model's predicted sequence. The temperature-scaled softmax bar chart per token provides a visual representation of the probabilities assigned by the model to each possible next token.

The perplexity and match-rate trace give quantitative measures of how well the generated tokens align with the original text, offering insights into the model’s accuracy and confidence.

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Why It Matters

Understanding FIM is crucial for evaluating AI models' capabilities in natural language processing (NLP) tasks, especially those involving programming languages. This technique can help in developing more accurate and context-aware code generation tools.

Moreover, observing the model's decision-making process through FIM provides valuable insights into how machine learning algorithms learn from large datasets and make predictions.

Real-World Applications

FIM can be applied in various scenarios where code generation is needed, such as automated debugging, code refactoring, and even the creation of new software components. By understanding how models predict missing parts, developers can improve their tools and practices.

Additionally, FIM aids researchers in fine-tuning models for better performance on specific tasks, ensuring that AI-generated code meets high standards of quality and reliability.

Frequently asked questions

What does the temperature-scaled softmax bar chart represent?

The temperature-scaled softmax bar chart shows the probability distribution over possible next tokens. Lower temperatures make the probabilities more peaked, favoring higher-probability tokens, while higher temperatures spread out the probabilities.

How does top-k truncation affect FIM predictions?

Top-k truncation limits the model to consider only the k most probable next tokens. This can help in reducing ambiguity and focusing on more relevant completions, but it may also limit the diversity of generated code.

What is perplexity in FIM?

Perplexity measures how well a probability distribution or model predicts a sample. In FIM, it quantifies the model's uncertainty about its predictions, with lower values indicating better alignment between the generated and original code.

Why is source order important in FIM?

Source order provides context for the AI model to understand where in a code snippet the missing part should fit. This helps the model generate more coherent and contextually appropriate completions.

Try it live

Everything above runs in your browser — open Fill-in-the-Middle: AI Code Infilling (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Fill-in-the-Middle: AI Code Infilling (2D) simulation

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