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Needle in a Haystack

Needle in a haystack is an evaluation test measuring a model's ability to retrieve a single specific piece of information ("the needle") hidden inside a very long context ("the haystack"). You insert a target sentence at an arbitrary point in a text of tens of thousands of tokens and ask the model to recover it. Example: inside a long novel you hide "the secret code is ORANGE-7" at 60% of the text, then ask "what is the secret code?". The test checks whether the model finds it regardless of position, revealing blind spots (often tied to the lost-in-the-middle effect).

Definition

Use it to assess a model's or a RAG pipeline's reliability on long contexts before production. A good score gives you confidence the model will not "lose" critical data buried in extended documents.

Related terms

• Lost in the Middle
• Context Window
• Context Stuffing
• Grounding
• RAG (Retrieval Augmented Generation)

More in Prompting

• Prompt
• Prompting
• Role Assignment
• Zero-shot
• Few-shot
• Chain of Thought
• Prompt Engineering
• Output Format

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