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reval is a pure Go library for computing standard evaluation metrics used in information retrieval and natural language generation. It has zero external dependencies — only the Go standard library.
The module path is github.com/itsubaki/reval. All exported functions live in the reval package.

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When to use reval

reval is useful when you need to measure the quality of systems that rank or generate text:
  • Search engines — measure how well results match user intent with Precision@K, MAP, and NDCG
  • Recommendation systems — evaluate ranked item lists against known relevant items
  • Text summarizers — compare generated summaries to reference text using ROUGE
  • RAG pipelines — assess retrieval quality and generation quality in a single library

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Metric families

reval provides five metric families:
All ranking metrics accept graded (integer) relevance scores, not just binary labels. This lets you express degrees of relevance rather than a simple relevant/not-relevant judgment.

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Module path

Install and import the library using the module path github.com/itsubaki/reval:
The library requires Go 1.24.5 or later.

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Next steps

Quickstart

Install reval and compute your first metric in minutes.

Precision & MAP

Precision@K, Average Precision, and Mean Average Precision.

ROUGE

ROUGE-1, ROUGE-L, and ROUGE-Lsum for text overlap scoring.

BERTScore

Semantic similarity scoring with dense vector embeddings.