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siftwise

Run only the tests your change needs, safely.
Self-hosted test selection and failure triage for agent-driven CI.

Quickstart · Architecture · Eval results · Eval methodology · Changelog · Contributing

CI License: Apache-2.0 Python 3.11+ Status: alpha

2,049 / 2,050 real failures caught replaying rdflib's CI (the miss: a flaky test) · /select in ~0.4 s on 18,000 tests · self-hosted, Apache-2.0

siftwise is a self-hosted service for teams whose CI is flooded with pull requests, many of them now written by coding agents. It records every CI test result, picks the tests a change can affect (running the full suite whenever it isn't sure), and tells people and agents whether each failure is a new regression, already broken on main, or flaky. What sets it apart: it runs on your own Postgres with no test instrumentation; it fails open, so a siftwise outage never blocks CI; it ships an MCP server, so coding agents ask which tests to run and why a test failed; and its shadow mode measures, on your own CI, how often a selection would have missed a real failure before you rely on it. Why now: Anthropic reports a 25x increase in CI jobs over six months as agents sped up writing code (Agentic coding is straining CI), and Linear found that as development accelerates, CI becomes a bottleneck, because every PR still has to pass through it (AI coding has made CI a bottleneck).

Status: alpha (0.1.0). Evaluated on four real repos' CI history. APIs and the database schema may change before 1.0.

siftwise select on an rdflib commit: 325 test files import the changed modules, 17921 of 18020 known tests selected, and a pytest command

The sticky PR comment on a shadow run: what siftwise would have run, each failure with its verdict, and the failure the selection would have missed, with its cause.

siftwise PR comment: would have run 197 of 900 tests, two failures with verdicts, and one missed test with its cause, new test

How it works

flowchart LR
    A["CI run, PR or<br/>agent branch"] --> B["siftwise select<br/>(git diff + import graph)"]
    B --> C[("siftwise server<br/>Postgres per-test history")]
    C --> D["test command<br/>+ reasons"]
    D --> E["run tests"]
    E --> F["record JUnit"]
    F --> C
    F --> G["rollup: triage verdicts<br/>+ shadow compare"]
    G --> H["PR comment"]

Full details: ARCHITECTURE.md.

  • Record. CI uploads JUnit XML with the commit, branch, changed files and what the change links to. The server keeps every result and rolls up per-test history.
  • Select. The CLI diffs your branch and builds Go or Python import graphs locally; the server returns the tests the change can affect, each with a reason, or the full suite when the diff, a build file or the history leaves any doubt.
  • Triage. Each failure gets a verdict (new regression, pre-existing on main, flaky, unknown) with a confidence and its evidence, using only history from before the run.
  • Measure. Shadow runs run the full suite and report what the selection would have caught or missed, and why.

Quickstart

From zero to a first selection in about 5 minutes, on a small example project. You need Docker, git and uv. The commands are bash: on Windows, use Git Bash or WSL. CI runs the blocks below on every change (quickstart.yml), with the server image and the CLI built from the checkout.

git clone https://github.com/PramodBasavarajMenasi/siftwise.git
cd siftwise

1. Start the server with Postgres, from the published image (ghcr.io/pramodbasavarajmenasi/siftwise:0.1.0). The API token is a shared secret you choose; it goes in .env, which docker compose reads:

[ -f .env ] || echo "SIFTWISE_API_TOKEN=$(openssl rand -hex 32)" > .env
docker compose up -d --wait             # pulls the image, waits until both services are healthy
curl -fsS http://localhost:8000/healthz # {"status":"ok"}

To run the server from your checkout instead (when you change it), add --build.

2. Install the CLI (the light install, without the server's dependencies) and give it the token:

uv tool install siftwise                # or: pip install siftwise
export SIFTWISE_API_TOKEN=$(sed -n 's/^SIFTWISE_API_TOKEN=//p' .env)

If siftwise isn't found afterwards, run uv tool update-shell once and open a new shell.

3. Record a first run. Copy the example project into a git repo of its own, run its tests with a JUnit report, and upload the report:

demo="$(mktemp -d)/shop" && cp -r examples/quickstart "$demo" && cd "$demo"
git init -q && git add -A && git commit -qm "A shop"
uv run pytest -q --junitxml=junit.xml
siftwise record junit.xml --repo demo/shop --branch main --main

4. Change a file and ask what to run. shop/cart.py changes; only the cart's tests import it:

echo "# reviewed the bulk discount" >> shop/cart.py && git commit -qam "Touch the cart"
siftwise select --repo demo/shop --base HEAD~1 > selected.sh
cat selected.sh                         # pytest tests/test_cart.py
uv run sh selected.sh

The command goes to stdout (so eval "$(siftwise select ...)" works, or a file as here) and a summary to stderr:

siftwise: python imports: 1 test file(s) import changed modules
siftwise: selective (2 of 4 known tests): 2 of 4 known tests selected

A change to shop/prices.py selects both test files instead (the cart imports prices). --json prints the full response with a reason per test. Exit codes: 0 ok, 1 API error, 2 usage error, 3 full suite needed but no command known. docker compose down stops the server (down -v also deletes its data).

On your own project: record each CI run's JUnit report (the GitHub Action does it for you, or siftwise record below), then call siftwise select (or the Action's select step) on a change. In CI, check out with fetch-depth: 0 so the base...head diff works; if it fails, the full suite runs.

Install

Install What you get Size
pip install siftwise the CLI: select, record, triage, report, rollup, and the GitHub Action's steps 9 MB
pip install 'siftwise[server]' plus the API server: siftwise server start and migrate (FastAPI, SQLAlchemy, Postgres driver) 50 MB
pip install 'siftwise[mcp]' plus siftwise mcp, for coding agents 49 MB

For a command-line tool, uv tool install siftwise (or pipx install siftwise) gives it its own environment; add the extras the same way (uv tool install 'siftwise[mcp]'). From a checkout: uv tool install . (or ".[server]", ".[mcp]"). A command whose extra is missing exits 2 and prints the install command. siftwise --version prints the version.

Run the server

With Docker, from the published image:

docker run -d -p 8000:8000 -e SIFTWISE_API_TOKEN=... \
    -e SIFTWISE_DATABASE_URL=postgresql+psycopg://user:password@db-host:5432/siftwise \
    ghcr.io/pramodbasavarajmenasi/siftwise:0.1.0

To build the image from a checkout instead: docker build -t siftwise ., then run siftwise in place of the image name.

  • The image (about 80 MB to pull, 350 MB unpacked) runs siftwise server start as a non-root user: it applies the database migrations, then serves on port 8000. Migrations take a Postgres lock, so several replicas can start at once. A Docker health check calls /healthz.
  • Without Docker: pip install 'siftwise[server]', then siftwise server start --host 0.0.0.0 (siftwise server migrate applies the migrations alone).
  • Reaching it from CI: the quickstart's docker-compose.yml publishes the API on 127.0.0.1 only (port SIFTWISE_PORT, default 8000) and keeps Postgres inside Docker. Put the server behind a reverse proxy with TLS: the token travels in a request header.
  • Upgrading: change the image tag to the new version (the quickstart's docker-compose.yml names it; a newer checkout already has it), then docker compose up -d: the new image migrates the database when it starts. Never go back to an older image: once the database has a migration that image doesn't know, its siftwise server start fails with Can't locate revision ... and the container restarts in a loop. If you build from a checkout (--build), rebuild after every pull for the same reason. A few migrations need a step after them: see the migration notes.

Seed history from past CI runs

Backfill a repo's past GitHub Actions runs (here rdflib, which uploads one JUnit artifact per matrix leg) instead of waiting for new ones. GITHUB_TOKEN needs actions:read and contents:read:

export GITHUB_TOKEN=...
uv run python scripts/backfill.py --repo RDFLib/rdflib --workflow validate.yaml \
    --artifact-pattern '*-pytest-junit-xml' --max-runs 20 --batch

Record results from other CI systems

On GitHub, use the GitHub Action. Elsewhere, upload JUnit XML after each test run:

siftwise record junit.xml --repo acme/shop --branch feature-x --ci-run-id 1234 \
    --base origin/main --started-at "$(date -u +%Y-%m-%dT%H:%M:%SZ)"

Uploads are idempotent per (repo, ci_run_id, run_attempt, variant): a re-upload stores nothing new. For a matrix, give each leg a --variant (e.g. ubuntu-py3.12) and --defer-rollup, then run siftwise rollup --repo acme/shop once after all legs. With --base, record also stores what the change links to, which triage needs to tell whether a later failure was related to this run's change.

Triage from the CLI

siftwise triage reads a run's JUnit reports and its diff, and gives each failing test a verdict:

siftwise triage junit.xml --repo acme/shop --base origin/main --variant ubuntu-py3.12 \
    --ci-run-id 1234 --fail-on new_regression
new_regression  high   tests.test_cart::test_total
    tests/test_cart.py tests changed src/cart.py
pre_existing    high   tests.test_db::test_query
    failing on main on ubuntu-py3.12 since 4f2a9c1 (3 main runs)
flaky           medium tests.test_net::test_fetch
    flaky 1 time in 90 days (1 unrelated fail-then-pass)
siftwise: 3 failing test(s): 1 new regression, 1 pre existing, 1 flaky, 0 unknown

The rules, in order, are in the architecture doc. Only runs before the triaged one count, so triaging an old run gives the answer it would have got live. --json prints the verdicts with their evidence. Exit codes: 0 ok, 1 API error, 2 usage error, 4 a failure got a --fail-on verdict (off by default). 500 failures on rdflib take about 0.25 s.

GitHub Action

Three composite actions in this repo. They install the light CLI from the action's own checkout and never block CI: if the server is unreachable, times out or returns an error, select outputs mode: full and record/rollup log a warning. The only exception is fail-on, which you opt into.

Action When What
actions/select before tests picks tests; outputs mode, command, selected, total, reason, junit-dir (and the shadow outputs); posts one sticky PR comment and a job summary
actions/record after tests, if: always() uploads JUnit with the run ID and attempt, the PR head commit (not the merge commit), branch, variant, start time, changed files and known_flaky; optionally re-runs unknown failures; in a single job, then triages the failures and reports a shadow run
actions/rollup once after a matrix triages the failures of every leg and reports a shadow run, then updates test stats once for all legs

Setup:

  • Secrets: SIFTWISE_URL (your server) and SIFTWISE_TOKEN (its SIFTWISE_API_TOKEN).
  • Permissions: contents: read, actions: read (the run's start time) and pull-requests: write (the comment).
  • Full history: check out with fetch-depth: 0. select fails with a clear message on a shallow clone, the only way it fails.
  • Version: the examples use @main; pin a release tag (@v0.1.0) or a commit SHA for reproducible CI. The actions install the CLI from their own checkout, so the CLI's version always matches the tag.

Never use these actions with pull_request_target. That event runs with secrets on code from the PR, so a fork could read your siftwise token. Use pull_request: on fork PRs, secrets are empty, so select runs the full suite and skips the comment, record skips the upload, and there are no failure verdicts.

Single job

name: CI
on:
  push:
    branches: [main]
  pull_request:
permissions:
  contents: read
  actions: read
  pull-requests: write
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v7
        with:
          fetch-depth: 0
      - uses: actions/setup-python@v7
        with:
          python-version: "3.12"
      - run: pip install -r requirements.txt   # your install step

      - id: siftwise
        uses: PramodBasavarajMenasi/siftwise/actions/select@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}

      - name: Tests
        env:
          MODE: ${{ steps.siftwise.outputs.mode }}
          COMMAND: ${{ steps.siftwise.outputs.command }}
          JUNIT_DIR: ${{ steps.siftwise.outputs.junit-dir }}
        run: |
          if [ "$MODE" = selective ]; then
            # Shell-quoted by siftwise; each pytest command writes its own report to JUNIT_DIR.
            if [ -n "$COMMAND" ]; then eval "$COMMAND"; else echo "No tests affected."; fi
          else
            pytest --junitxml="$JUNIT_DIR/full.xml"   # your normal full suite
          fi

      - if: always()
        uses: PramodBasavarajMenasi/siftwise/actions/record@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}

Pass the command through env: as above, never as ${{ }} inside run:, so the shell sees it once, quoted. record uploads **/junit*.xml plus everything in the select step's junit-dir (its junit input takes other globs). For Go, write JUnit with gotestsum --junitfile or go-junit-report.

Matrix

Each leg records its own variant and skips the per-upload stats rollup; one rollup job runs after every leg:

jobs:
  test:
    strategy:
      matrix:
        os: [ubuntu-latest, macos-latest]
        python: ["3.11", "3.12"]
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v7
        with:
          fetch-depth: 0
      # ... set up Python and install, as above ...
      - id: siftwise
        uses: PramodBasavarajMenasi/siftwise/actions/select@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}
          comment: ${{ strategy.job-index == 0 }}   # one leg comments, or they race
      # ... the Tests step, as above ...
      - if: always()
        uses: PramodBasavarajMenasi/siftwise/actions/record@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}
          variant: ${{ matrix.os }}-py${{ matrix.python }}

  siftwise-rollup:
    needs: test
    if: always()
    runs-on: ubuntu-latest
    steps:
      - uses: PramodBasavarajMenasi/siftwise/actions/rollup@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}

The rollup job needs no checkout: the server already has what each leg recorded.

Failure verdicts

After the run's last upload (rollup after a matrix, record in a single job: its triage input, auto, true or false), siftwise triages the failing tests from what the uploads stored, including the change links record computed. The sticky PR comment gets a Failures section under the selection:

  • a summary line, e.g. "2 new regressions, 1 unknown, 1 flaky, 1 pre-existing", counting each test once, under its worst verdict over the legs;
  • a table of test, verdict, confidence, legs and one reason: new regressions first, then unknown; flaky and pre-existing collapsed below. all means every recorded leg got that verdict;
  • at most 20 rows per table, then "+N more"; the job summary has the full list (up to 500).

The comment is left alone if the PR got new commits since the run started, and a new push's selection drops the old commit's failures. Raw failure messages are never shown (the comment is public). Outputs: verdicts-available, counts (JSON, per verdict) and report (the summary's Markdown, as a file). How each verdict is decided: triage verdicts.

fail-on

fail-on (on rollup, or record in a single job) fails the step when a failure gets one of the listed verdicts, on any leg:

      - uses: PramodBasavarajMenasi/siftwise/actions/rollup@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}
          fail-on: new_regression,unknown
  • It can only add a failure. A leg whose tests failed is already red. To let siftwise decide, give the test steps continue-on-error: true and make the rollup job the required check.
  • Gate on new_regression,unknown. new_regression alone lets unknown through, and unknown is common (a new test, an unknown diff, an unrelated failure with no flaky history).
  • With fail-on set, unavailable verdicts fail the step too (fail closed): a server that's down or erroring, a timeout, or nothing recorded for the attempt. A real failure can't pass while siftwise is unreachable.
  • Except without a siftwise token: fork PRs get no secrets, so the step warns fail-on skipped: no siftwise token (fork PR?); this run is not gated and passes. Keep another required check on fork PRs. A missing SIFTWISE_TOKEN secret on your own repo looks the same: watch for that warning.
  • A PR can't excuse its own failures with known_flaky: record applies the PR base commit's list (Flaky tests).

Without fail-on (the default), siftwise never fails anything.

Flaky tests

Two ways to keep known flakes from reading as regressions, both in record:

      - if: always()
        uses: PramodBasavarajMenasi/siftwise/actions/record@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}
          rerun-unknown: 2         # re-run unknown failures up to twice
          rerun-prefix: uv run     # how pytest runs in your job (e.g. poetry run)
  • known_flaky in .siftwise.toml: a failing listed test not linked to the change is flaky (medium); linked, it's unknown ("re-run to tell"). For a pull request, record applies the base commit's list (known-flaky-source: base, the default), so a PR can't mark its own failures flaky; when the PR changes the list, the comment says "known_flaky changes in this PR apply after merge". known-flaky-source: head applies the PR's own list instead. A push always applies its own.
  • rerun-unknown: N (0 to 3, default 0): after uploading, record triages its own leg, re-runs failures whose verdict is in rerun-verdicts (unknown, or unknown,new_regression) with pytest node IDs, and records each re-run. A test that passes on one is flaky, high; one that fails again keeps its verdict, with a note.
  • Limits: at most rerun-max-tests tests (20) within rerun-timeout-minutes (10) for all rounds. pytest only; tests whose file isn't in the checkout aren't re-run. rerun-prefix is split like a shell would, and the command runs without a shell.
  • Fail open: any problem is a warning and the verdicts stay what they were. Re-runs never turn a red job green; the PR comment and fail-on use the verdicts after them. Outputs: rerun-tests, rerun-passed.

Shadow mode

How often would siftwise's selection have missed a real failure? On a sampled run the full suite runs while siftwise stores what it would have selected; after the run is recorded, the server checks every failure against that selection:

      - id: siftwise
        uses: PramodBasavarajMenasi/siftwise/actions/select@main
        with:
          server-url: ${{ secrets.SIFTWISE_URL }}
          token: ${{ secrets.SIFTWISE_TOKEN }}
          shadow: 10%          # or always; off by default
  • Sampling: off (default), always, or a percentage of CI runs, by a hash of the run ID, so every matrix leg and re-run attempt agrees. Matrix legs can set variant on select (the same value as record's) to store a selection per leg.
  • A shadow run always runs the full suite and records its results as usual; shadow mode never fails or shortens a run.
  • The report: where verdicts are computed, the PR comment and job summary get a line like "Shadow run: would have run 197 of 900 tests (56% time saved) and caught 1 of 2 failures", then each missed test with its cause (see the screenshot above). Time saved is measured on the run's own durations. Failures triage calls flaky are counted apart, never as misses.
  • Not counted, with a warning: a selection the server couldn't store, siftwise unreachable at select time, or a comparison that failed.

Recall over time comes from GET /repos/{repo}/recall?days=30, or siftwise report (example output):

siftwise report --repo acme/shop --days 30
# Recall 98.7% (148 of 150) over 40 shadow runs; selective runs only: 96.0% (48 of 50) over 25

The first figure counts every shadow run, including those where siftwise would have run the full suite anyway, so the report always shows the selective-only figure next to it. Below come the misses by verdict and cause, the measured time saved, the runs not counted, and each miss. --by week prints the same per week:

Week of     Runs  Recall (all)        Selective  Recall (selective)  Caught  Missed  Time saved
2026-09-28    11  100.0% (41 of 41)           7  100.0% (13 of 13)       41       0         38%
2026-10-05    12  98.0% (49 of 50)            8  95.0% (19 of 20)        49       1         41%

Each miss gets a cause, from evidence the server already has:

Cause Evidence
new_test no result for the test before the run
flaky_history flaky before, but not called flaky this time
config_gap a non-code file (data, fixture, golden file) changed in the test's own directory, which no import graph follows; the report suggests a [[depends]] rule for you to review
no_link the change is known and nothing in it links to the test (the report lists what changed)
unknown the run's change links weren't recorded, or the test was linked but not selected (the report warns: possibly a selector bug)

action-e2e.yml runs all three actions against a real server on every push and PR of this repo: verdicts, fail-on, a shadow run with a miss, known_flaky and rerun-unknown.

Coding agents (MCP)

siftwise mcp is an MCP server (stdio) that gives a coding agent three tools. It keeps no state: each call computes the change in the agent's checkout, with the same code as siftwise select, and asks the siftwise server. It never records runs.

Tool The agent calls it Returns
select_tests before running tests after a change mode, the command to run, the selected tests with a reason each
triage_failure when tests fail, before trying to fix them a verdict per failure (from JUnit paths or test IDs), with reasons and evidence
explain when a selection or verdict surprises it one test's recent results, flaky evidence, broken-on-main status, and why it would (not) be selected
  • Uncommitted work counts. The diff runs from the merge base of the base branch and HEAD to the working tree, untracked files included. When the tree is dirty, triage sends no commit, so "passed on this commit before" can't apply.
  • Fails open. If the server is down, errors or no token is set, select_tests says to run the full suite and triage_failure says verdicts are unavailable.
  • Compact output. Each result stays under 8,000 characters. The API token never appears in a result.

Install the CLI with the mcp extra (Install):

uv tool install 'siftwise[mcp]'  # siftwise lands in ~/.local/bin (Windows: %USERPROFILE%\.local\bin)
uv tool update-shell             # once, if that directory isn't on your PATH; then restart the agent
uv tool dir --bin                # prints the directory, for a full path in the configs below

The agent starts the server in its working directory: open the agent in the repository. It reads SIFTWISE_SERVER and SIFTWISE_API_TOKEN, and optionally SIFTWISE_REPO (default: owner/name from the origin remote) and SIFTWISE_BASE_REF (default: the branch origin/HEAD points to, else main). Keep the token out of files you commit: use your user-level config, or environment-variable expansion where the client has it.

Claude Code:

claude mcp add siftwise --env SIFTWISE_SERVER=https://siftwise.example.com \
    --env SIFTWISE_API_TOKEN=your-token -- siftwise mcp

or a project .mcp.json, which expands ${VAR} from your environment:

{
  "mcpServers": {
    "siftwise": {
      "command": "siftwise",
      "args": ["mcp"],
      "env": {
        "SIFTWISE_SERVER": "https://siftwise.example.com",
        "SIFTWISE_API_TOKEN": "${SIFTWISE_API_TOKEN}"
      }
    }
  }
}

Codex (~/.codex/config.toml):

[mcp_servers.siftwise]
command = "siftwise"
args = ["mcp"]
env = { SIFTWISE_SERVER = "https://siftwise.example.com", SIFTWISE_API_TOKEN = "your-token" }

Cursor (~/.cursor/mcp.json for every project, or .cursor/mcp.json in one): the same JSON as .mcp.json above, with the token value written in.

If the agent can't find siftwise (it doesn't see your shell's PATH, common on Windows), give the full path from uv tool dir --bin as the command. In JSON, double the backslashes ("C:\\Users\\you\\.local\\bin\\siftwise.exe"); in TOML, use a single-quoted string.

Then tell the agent when to use it, e.g. in AGENTS.md or CLAUDE.md:

Before running tests, call the siftwise `select_tests` tool and run the command it returns.
When tests fail, call `triage_failure` before fixing anything: fix `new_regression` failures,
re-run `flaky` ones, and leave `pre_existing` ones (already failing on main).

Configuration

.siftwise.toml at the root of the repo being tested, read by the CLI, the Action and the MCP server:

always_run = ["tests/smoke/**", "tests.test_health::*"]  # test file paths or test IDs
generated = ["build/reports/**"]          # more files your test runs write (see below)
known_flaky = ["tests/test_net.py"]       # triage: unlinked failures are flaky

[[depends]]                               # dependencies no import graph can see
tests = "test/cli/**"                     # test file paths, or <Go package dir>/<TestName>
on = ["**/*.go", "!**/*_test.go"]         # ! excludes
  • Globs: ** spans directories, while * and ? stay within one path segment (tests/* matches tests/test_a.py, not tests/unit/test_b.py). Go test IDs contain their package's import path, so match them with **::TestName or <import path>::*.
  • Generated files never count as changed code, even untracked or committed by mistake: junit*.xml, coverage.xml, .coverage, .coverage.*, htmlcov/, *.log, .pytest_cache/ and __pycache__/, at any depth. generated adds to that list.
  • known_flaky is for triage only (selection still runs listed tests); CI applies a pull request's base list (Flaky tests).
Variable Used by Default
SIFTWISE_API_TOKEN server (required: if unset, every endpoint but /healthz returns 503) and clients none
SIFTWISE_SERVER clients: the CLI's --server, MCP, the Action's steps http://localhost:8000
SIFTWISE_DATABASE_URL server postgresql+psycopg://siftwise:siftwise@localhost:5432/siftwise
SIFTWISE_STATS_WINDOW_DAYS server: per-test stats window (0 = all history) 90
SIFTWISE_MAX_UPLOAD_BYTES server: request body limit 50 MB
GITHUB_TOKEN scripts/backfill.py none

Supported languages:

Language Selection Commands
Python (pytest) foo.py → test_foo.py; test files importing a changed module (static graph incl. parent packages, conftests, plugin strings); changed test files pytest node IDs, whole test files, pytest --doctest-modules for doctests
Go changed package and every package whose tests import it (go list -deps -test) go test ./pkg (whole) or -run '^(TestA|TestB)$'
JS/TS (Jest) foo.ts → foo.test.*, foo.spec.*, __tests__/foo.* (needs file paths in the JUnit) jest <files>
Java (Maven/Gradle) recorded with full history; selection falls back to the full suite —

Results on real repos

Replays of real CI history with no peeking at the future, with the current code except where noted. How they measure, and what they don't prove: eval methodology; full numbers: eval results.

Repo Failures caught Test time skipped
ipfs/kubo (Go, ~4,100 tests), measured with the week-2 code 19 of 19 in failing PRs 30.7% over 20 main commits replayed as PRs; 0% on recent PRs (all dependency/CI bumps)
RDFLib/rdflib (Python, ~18,000 tests) 2,049 of 2,050 in 39 failing PRs; 140 of 141 in selective runs. The miss is a flaky remote-service test 10.4% on the 10 most recent PRs; 0.6% over 19 main commits
quantumlib/Cirq (Python monorepo, 9 packages, ~40,000 tests) not measurable: JUnit only from main, which never failed 37.9% over 132 merged PRs; 79.8% for cirq-google-only PRs, 20.2% for cirq-core
agent-substrate/substrate (Go, ~9,000 tests, 8 days of history) 2,043 of 2,044 in 72 failing PRs; 38 of 39 in selective runs, with declared rules for its e2e and functional suites (26 of 38 without them, week-3 code) 5.1% on PR runs and 13.9% over 40 main commits, with both rules (19.5% / 31.7% without rules, week-3 code)
  • Savings follow package boundaries. In the Cirq monorepo, a change to one integration package skips most of the suite; a change to the core package everything imports skips little. rdflib's __init__.py and plugin registry connect nearly every module to nearly every test, so safe file-level selection still runs ~99% of its suite (its 10.4% comes from lint-only PRs). Bigger savings need codebases with independent parts, or per-test coverage.
  • The misses: substrate's are end-to-end suites that drive a deployed system (no import edge reaches them; a declared dependency catches them at the cost of most of the savings) and flaky tests. rdflib's one miss, test_service_with_bound_solutions, calls a remote SPARQL service and had failed in unrelated runs before: it's flaky, which is what rerun-unknown is for.

Triage (a verdict per failure, scored against what happened next; details):

  • The worst error, a regression called flaky: 0 on rdflib. On substrate, 5 of 406 labelled regressions, all on tests with earlier same-commit flakes; 4 are likely label noise from merge diffs.
  • The prediction tests held up: new_regression 319 of 319 labelled substrate failures (and 10 of 11 rdflib fix episodes with a known diff), and medium-confidence pre_existing 759 of 759, each called after a single failing main run.
  • Flaky precision is mostly by construction: almost every flaky verdict is a pass of the same commit seen before the failure, which is also the flaky label's evidence.

Performance (rdflib history; results identical before and after; details): triage of a 22-variant CI run 1,032 → 220 ms (180 → 12 queries, no longer growing with variants); the selection inside /select 605 → 237 ms; ingesting a 9,891-result upload about 2.2 → 1.25 s.

How it compares

From each project's public docs as of October 2026; corrections welcome.

Open source Self-hosted Languages How it selects Agent/MCP support
siftwise Yes (Apache-2.0) Yes Python, Go, JS/TS file mapping, Go/Python import graphs, failure history MCP server (select, triage, explain)
CloudBees Smart Tests No Not stated Many (runner integrations incl. Python, Go, Java, JS) LLM analysis of changes + test history Not documented
Datadog Test Impact Analysis No No (Datadog SaaS) JS/TS, Java, Python, Go, Swift and more per-test code coverage Not documented
Develocity Predictive Test Selection No Yes (Develocity server) Gradle and Maven builds predictive model from past builds Not documented
pytest-testmon Yes (MIT) Local plugin, no server Python (pytest) per-test code coverage No

Coverage-based tools see dynamic dependencies that static graphs miss, but they need instrumented runs. siftwise uses no instrumentation; when its graphs can't see a dependency, the fallbacks and .siftwise.toml cover it.

Security and limits

Found a vulnerability? Report it privately, as SECURITY.md describes, not in a public issue.

  • One token per server, with full access. SIFTWISE_API_TOKEN is a single shared secret: every client (CI, the CLI, the MCP server) uses it, and it can read and write the history of every repo on the server. There are no per-repo, read-only or per-user tokens. Run a separate server for repos whose owners shouldn't see each other's history, and rotate the token by changing it on the server and in each secret.
  • Keep the token out of fork PRs. Use pull_request, never pull_request_target: a fork's code must never run with the token.
  • Protect your workflows. The base-branch known_flaky rule assumes the workflow itself is protected. A PR that edits .github/workflows/ can change any gate, so protect workflows with CODEOWNERS or a ruleset.
  • What the server stores: test IDs, outcomes, durations, failure messages (truncated to 4 KB), changed file paths, branch names and commit SHAs. Failure messages can contain whatever your tests print, so treat the database as you treat CI logs. Public PR comments show test IDs, verdicts and siftwise's own reasons, never raw failure messages.
  • Stats cover the window only. Per-test stats use the last SIFTWISE_STATS_WINDOW_DAYS (90) days before the repo's newest run; older raw results stay, but no longer feed stats.
  • Limits to know: merge-queue (merge_group), scheduled and manual runs always run the full suite (no diff base); the Action is tested on Linux runners only; Java tests are recorded but always run in full; rerun-unknown re-runs pytest only.

Roadmap

  • Done: recording and history, test selection with import graphs and safe fallbacks, the GitHub Action, failure triage with verdicts in the PR comment and fail-on, the MCP server, the triage eval, shadow mode with siftwise report, miss causes, flaky handling (known_flaky, rerun-unknown), performance (batched triage, faster select and ingest), packaging (a light CLI, a server image, the quickstart) and the v0.1.0 release on PyPI and GHCR (changelog).
  • Next: a demo and the launch write-up; an arm64 server image.
  • After launch: live dogfooding: shadow mode on siftwise's own CI with a hosted server, with published live recall numbers.

Contributing

Issues and pull requests are welcome: see CONTRIBUTING.md for the dev setup, the checks and the PR checklist, and ARCHITECTURE.md for how the pieces fit. Everyone taking part follows the Code of Conduct.

License

Apache-2.0

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