A retrieval test suite rests on one assumption nobody writes down: that every label still points at the passage a human actually read. Labels are stored as chunk IDs, and chunk IDs are an artifact of your chunker. Change the chunk size, the splitter or the overlap, and the IDs move while the labels stay where they were. Nothing errors. The metrics keep computing, against ground truth that is partly no longer there.

One command shows you how much:

retrieval-eval drift --judgments judgments.jsonl --corpus corpus.json

  312 judgments · labeled @ fingerprint recursive/512
  live corpus    @ fingerprint recursive/384

  ok  188  VALID          chunk_id still present
  !    47  RE-ANCHORABLE  text moved to a new chunk_id
  !    24  MERGED         text absorbed into a coarser chunk
  !    34  SPLIT          labeled text now spans 2+ chunks
  x    19  ORPHANED       source text or document is gone

  40% of your judgment set no longer matches the live corpus.
  Any metric computed against it is measuring two changes at once.
  71 recoverable automatically · 53 need a human

  next    retrieval-eval drift --fix, to re-anchor the recoverable labels

You changed your chunker. Your recall@5 moved 0.06. You credited the change.

But 40% of your labels no longer point at the text a human actually read. Part of that movement was your test suite decaying, not your retriever improving, and no other evaluation tool will tell you which part.

retrieval-eval separates them, then recovers the labels it can:

retrieval-eval drift --judgments judgments.jsonl --corpus corpus.json --fix
#   fixed   re-anchored 71 label(s) in judgments.jsonl
#   review  53 label(s) still need a human

RE_ANCHORABLE and MERGED are recoverable: the text a human judged is still there, either as its own chunk or inside a bigger one. SPLIT and ORPHANED are left alone on purpose, because guessing at them would fabricate ground truth, which is the exact failure this tool exists to expose.

See it happen in 30 seconds. examples/quickstart runs a corpus whose text never changes, re-chunks it, and watches recall@3 fall from 1.00 to 0.00 while retrieval stays perfect, then brings it back with --fix. Six more runnable scenarios, the integration for eight stacks, and complete CI jobs are in examples/.

Why this matters

A golden set is the most expensive thing in a RAG project. Every label is a person reading a passage and deciding whether it answers a question. Yet it is the one artifact nothing checks. Retrievers get versioned, prompts get diffed, embedding models get benchmarked, and the labels underneath all of them are treated as permanent. They are coordinates into one particular chunking, and every chunking change moves the map.

The damage is quiet, and it points the wrong way. A chunker that genuinely retrieves better can score worse, because its correct answers now live under IDs the labels have never seen. A real improvement and the decay it caused can cancel out and read as no change at all. Either way, the number you gate releases on is measuring two things at once, and nothing tells you how much of each.

Teams that notice end up with three bad options: relabel from scratch, stop trusting the suite, or stop changing the chunker. drift is a fourth. It names exactly which labels moved, recovers every one whose text is provably still there, and sends only the rest to a human. After that, your metrics are measuring your retriever again.

Install

pip install retrieval-eval        # or: uvx retrieval-eval --help

Same name, same commands, same flags, same rendered output, same exit codes in both, so one CI step works for a polyglot team. Node 20.11 or newer, Python 3.10 or newer.

What it does

1. Keeps your labels true when the corpus changes. Every chunk gets an identity derived from its content, not its position (the one idea), so a label remembers what a human read rather than where it used to sit. drift classifies every label as VALID, RE_ANCHORABLE, MERGED, SPLIT or ORPHANED, --fix repairs the two recoverable classes in place, and the command exits non-zero on decay, so a re-chunk cannot ship with a stale suite behind it. Run it before score, in CI, on every chunking change.

2. Measures retrieval, deterministically. precision@k, recall@k, ndcg@k, mrr@k, map@k, hit_rate@k. Every metric carries its cutoff in its name, because a number that means something other than its name is how a report stops being trustworthy. No model call, no API key, no per-run cost, milliseconds per run.

These are the metrics that localize a failure. High recall@20 with low recall@5 means retrieval found the answer and ranking buried it, so the reranker is the problem rather than the chunker. A single end-to-end score cannot make that distinction.

retrieval-eval score --judgments judgments.jsonl --run hits.jsonl -k 5 \
  --baseline .retrieval-eval/baseline.json \
  --gate recall@5:-0.02 \
  --gate worst-stratum:recall@5:0.7

3. Refuses to let an average hide a broken query class.

  recall@3 by stratum
  · legal                0.0000  ░░░░░░░░  n=2  worst
  · billing              1.0000  ████████  n=3

  gates
  ok recall@3:0.5
  x  worst-stratum:recall@3:0.7

Overall recall is 0.60 and passes an average gate. Legal queries retrieve nothing. That is why stratum is a field in the format, per_stratum is mandatory in the report, and worst-stratum gating is a first-class gate.

4. Speaks TREC qrels, so thirty years of tooling just works.

retrieval-eval convert --judgments judgments.jsonl --to qrels | trec_eval -m all_trec - run.txt
retrieval-eval convert --qrels beir/scifact/qrels/test.tsv --to judgments > judgments.jsonl

A judgments file is a strict superset of qrels, so trec_eval, ir_measures, pytrec_eval, BEIR and ir_datasets are all one conversion away in either direction.

5. Tells you when a judgment set is unsound, not merely malformed:

  warning [no-human-labels] every label is synthetic. Without human labels you cannot measure
          judge calibration, and synthetic labels quietly become ground truth
  warning [mixed-fingerprints] judgments span 2 corpus fingerprints; run 'drift' first
  warning [thin-stratum] stratum 'legal' has only 2 labels, too few to gate on
  error   [no-positives] no judgment has relevance >= 1, so recall is undefined

The one idea

Give every chunk an identity derived from its content, not its position:

chunk_id = "c1:" + sha256(doc_uri ␟ doc_revision ␟ ordinal ␟ normalize(text) ␟ chunker_fingerprint)[0..16]
#                    128 bits, written as 32 lowercase hex characters

A label then points at text a human read, so after a re-chunk the tool can say exactly which labels survived.

The spec is two JSON Schemas and one hash definition, small enough to implement in an afternoon in any language. If it ever needs a framework, it has failed. It ships inside both packages, so a port never has to start from the GitHub UI.

What this removes

Each row is a situation teams are already in.

Use it as a library

import { drift, score, chunkId, toQrels } from "retrieval-eval";

const result = drift(judgments, corpus);
if (result.summary.invalid_ratio > 0.1) throw new Error("golden set has decayed");

const { metrics } = score(judgments, run, { k: 5 });
metrics["recall@5"].value;

from retrieval_eval import drift, score, chunk_id, to_qrels

result = drift(judgments, corpus)
if result.summary.invalid_ratio > 0.1:
    raise RuntimeError("golden set has decayed")

scored = score(judgments, run, k=5)
scored.metrics["recall@5"].value

In CI

- run: pip install retrieval-eval
- run: retrieval-eval drift --judgments eval/judgments.jsonl --corpus eval/corpus.json
- run: |
    retrieval-eval score \
      --judgments eval/judgments.jsonl --run eval/hits.jsonl -k 5 \
      --baseline eval/baseline.json \
      --gate recall@5:-0.02 --gate worst-stratum:recall@5:0.7 \
      --out report.json

Exit 0 passed, exit 1 a gate failed or labels decayed, exit 2 bad invocation or unreadable input. drift exits non-zero on its own, so it works as a standalone check.

GitLab, CircleCI, Jenkins, Azure Pipelines and pre-commit recipes are in docs/ci.md.

Why this does not already exist

Every evaluation tool scores against a golden set. None of them checks whether the golden set still describes the corpus. RAGAS, DeepEval, promptfoo and the IR toolkits all store a label as a pointer and trust it forever, because no shared format records which corpus revision or which chunker a label was made against. Without that, drift is not merely unreported, it is unmeasurable. The judgment format here adds exactly the fields that make it measurable, and drift is the algorithm that uses them.

The metrics had a smaller gap of their own. Python has pytrec_eval, ir_measures and BEIR. On npm the package names you would reach for first, ndcg, ir-measures, trec-eval and qrels, are unpublished, and what does exist is thin: node-dcg computes DCG alone and was last published in 2023, trec-eval-wrapper shells out to the trec_eval C binary rather than implementing anything and was last published in 2022, and the recent entries are coupled to something else, an MCP server or a recommender engine's own core package.

So there are two gaps, in order of importance: nothing in either ecosystem treats judgment drift as a measurable condition, and no maintained, standalone, dependency-free IR evaluation library exists for JavaScript. The evidence, including the two claims this research falsified against its own earlier draft, is in research/.

(Registry state checked 2026-09-22. If this has changed, the claim is wrong and belongs in an issue. Accuracy about our own positioning is part of the point.)

It is not a replacement for judged evaluation

Retrieval quality is a large share of end-to-end RAG quality, not all of it. The rest is how well the model uses what it retrieved. This covers the retrieval half rigorously and deliberately does not claim to certify a RAG system.

Use it alongside RAGAS, DeepEval, promptfoo, Phoenix or Braintrust rather than instead of them. It makes their golden sets portable and durable, which is why interoperability is the strategy rather than a feature.

For the judged half, the report format carries the honesty those metrics need, and summarize() computes it: n, stdev and a confidence interval from repeated samples of the same judge, plus a third verdict, INDETERMINATE. LLM judges are non-deterministic even at temperature 0, so a ci-lower gate on a single sample says "I do not know" rather than guessing.

report.metrics["faithfulness"] = summarize([0.8, 1.0, 0.6, 0.9, 0.7])
#  value 0.8000, stdev 0.1581, 95% interval [0.6037, 0.9963]
#  the mean clears a 0.8 floor; the interval says you cannot tell yet

examples/judged-metrics runs that end to end in both languages.

Why zero dependencies

Both packages use only their standard library: sha256 and JSON. A measurement tool that drags in a dependency tree becomes a thing you skip installing in CI. It also keeps the spec implementable anywhere, which is the point of a spec.

Status

0.1.0, alpha. The formats and the metric mathematics are what we intend to keep. The CLI surface may still move. The c1: and t1: hash prefixes exist so identity can be versioned without breaking existing judgment files.

What is already load-bearing, and enforced on every commit:

• Parity. Both implementations run the same spec/fixtures through both CLIs and must agree on the numbers, the rendered output, the help text and the exit codes. Not two test suites that each pass, one job that runs both and diffs the result.
• Determinism. Same inputs, same output, every run. No network, no model, no clock in the numbers. Across the two implementations: rendered output and judgments files are byte-identical, and --json agrees as data rather than as bytes, because JSON writes a whole number as 1 in JavaScript and 1.0 in Python. Compare reports by parsing them, not by checksum.
• A quickstart that is executed, not described. CI runs the README's own first-run path on a clean checkout on Linux and macOS, and asserts the demo still demonstrates its claim.

Repo layout

spec/                        the contract: 2 schemas, 1 hash definition, shared fixtures
  fixtures/                  conformance cases BOTH implementations must pass
packages/retrieval-eval/     TypeScript (tsup · vitest · biome)
python/retrieval-eval/       Python     (hatchling · pytest · ruff · mypy --strict)
docs/                        CLI reference, CI recipes, interop, troubleshooting
examples/                    runnable scenarios, stack integrations, pipeline jobs
  frameworks/                LangChain, LlamaIndex, Haystack, Chroma, Qdrant, pgvector, RAGAS, DeepEval
  pipelines/                 Jenkins, GitHub Actions, GitLab, Azure, CircleCI, pre-commit
research/                    the evidence behind the design

Python and TypeScript are peers, not ports. Both read the same spec/fixtures and must agree to the twelfth decimal, which is what makes "parity by spec" a claim rather than a slogan.

Docs

License

Apache-2.0