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Fine-Tuning Data Preparation

Data volume guidelines, quality checklists, and the complete preparation pipeline for fine-tuning datasets.

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Production10 min readFirst readWhen to Fine-Tune: The Decision Framework

After this section you can

  • Estimate how many examples a task needs from how far it moves the model
  • Run a dataset through quality gates and catch leakage, template skew and label noise before training
  • Generate synthetic data and filter it with a signal independent of the generator
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Fine-Tuning Data Preparation

A fine-tuned model becomes whatever its examples are, mistakes included. How much data each task needs, the gates every example must pass, and how to format, select and generate it.

Key idea

Fine-tuning is imitation at scale. A thousand clean, varied, correctly labelled examples teach the task. Ten thousand scraped, duplicated, 5%-mislabelled ones teach the mistakes too, faithfully. Time spent on data buys more quality than any hyperparameter.

Five stages from raw examples to a versioned dataset, with gates that reject before training
EVERY EXAMPLE PASSES EVERY GATE, OR IT DOES NOT TRAIN 1 · Collect production logs, experts, seeded synthetic 2 · Clean fix labels, strip PII and secrets 3 · Dedup exact and near-duplicates, eval overlap 4 · Format one chat template, JSONL messages 5 · Split + version train / val / test, hash + dataset card Reject bin: keep it and read it duplicates · PII and keys · wrong or inconsistent labels truncated examples · anything overlapping the eval set A shrinking dataset is the pipeline working. Discarding a fifth to a half of raw data is common.

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