scherlok 0.2.2

A detective for your data. Zero-config data quality monitoring.

Scherlok

Your data broke in production. Again.
Scherlok makes sure it doesn't happen next time.

pip install scherlok
scherlok connect postgres://localhost/mydb
scherlok investigate
scherlok watch

Zero config. Zero YAML. Zero rules to write.
Scherlok learns what "normal" looks like, then tells you when something changes.

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The Problem

Every data team has the same nightmare:

A source API silently changes from dollars to cents. Revenue dashboards show wrong numbers for 3 weeks before anyone notices.

A column starts returning NULLs. A table stops updating. Row counts drop 40% on a Tuesday. Nobody knows until the CEO asks why the report looks weird.

Current tools (Great Expectations, Soda, dbt tests) require you to define what "correct" looks like before you can detect what's wrong. Hundreds of rules. Dozens of YAML files. And you still miss things — because you can't write rules for problems you haven't imagined yet.

The Solution

Scherlok takes the opposite approach: learn first, then detect.

scherlok connect postgres://user:pass@host/db   # connect once
scherlok investigate                              # learn your data
scherlok watch                                    # detect anomalies

Three commands. Five minutes. Done.

What It Catches

Anomaly	What Happened	Severity
Volume drop	Row count dropped 40% overnight	CRITICAL
Volume spike	3x more rows than normal	WARNING
Freshness alert	Table hasn't updated in 12h (normally every 2h)	CRITICAL
Schema drift	Column removed or type changed	CRITICAL
NULL surge	NULL rate jumped from 2% to 45%	WARNING
Distribution shift	Column mean shifted 5+ standard deviations	WARNING
Cardinality explosion	Status column went from 5 values to 500	CRITICAL

Every anomaly is auto-scored: INFO, WARNING, or CRITICAL. No thresholds to configure.

How It Works

1. investigate — Learn the patterns

$ scherlok investigate

  Profiling 12 tables...
  ✓ users         — 45,231 rows, 8 columns
  ✓ orders        — 1,203,847 rows, 15 columns
  ✓ products      — 892 rows, 12 columns
  ...
  Done. Profiles saved.

Scherlok profiles every table: row counts, column types, NULL rates, value distributions, freshness cadence, cardinality. Stores everything locally in SQLite.

2. watch — Detect anomalies

$ scherlok watch

  Checking 12 tables against learned profiles...

  🔴 CRITICAL  orders    volume_drop     Row count dropped 52% (1,203,847 → 578,412)
  🟡 WARNING   users     null_increase   Column "email": NULL rate 2.1% → 18.7%
  🔵 INFO      products  distribution    Column "price": mean shifted 3.2σ

  3 anomalies detected. Exit code: 1

3. Alert — Slack, CI/CD, or both

# Slack alerts
scherlok watch --slack https://hooks.slack.com/services/...

# CI/CD gate (fails pipeline on CRITICAL)
scherlok watch --exit-code --fail-on critical

CI/CD Integration

Use Scherlok as a data quality gate:

# GitHub Actions
- name: Data quality check
  run: |
    pip install scherlok
    scherlok connect ${{ secrets.DATABASE_URL }}
    scherlok watch --exit-code --fail-on critical

If Scherlok detects a critical anomaly, the pipeline fails. Bad data never reaches production.

Connectors

# PostgreSQL
scherlok connect postgres://user:pass@host:5432/db

# BigQuery
pip install scherlok[bigquery]
scherlok connect bigquery://project-id/dataset-name

Database	Status
PostgreSQL	Available
BigQuery	Available
Snowflake	Coming soon
MySQL	Coming soon
DuckDB	Planned

Remote Storage

Share profiles across CI runs and team members:

# AWS S3
scherlok config --store s3://my-bucket/scherlok/profiles.db

# Google Cloud Storage
scherlok config --store gs://my-bucket/scherlok/profiles.db

# Azure Blob Storage
scherlok config --store az://my-container/scherlok/profiles.db

Why Not [Other Tool]?

	Great Expectations	Soda	Monte Carlo	Scherlok
Setup time	Hours	30 min	Weeks	5 minutes
Config required	Hundreds of rules	YAML checks	Dashboard setup	None
Anomaly detection	Manual thresholds	Paid feature	Yes	Yes, free
Self-hosted	Yes	Limited	No (SaaS)	Yes
CI/CD gate	Yes	Yes	No	Yes
Price	Free	Freemium	$50-200K/yr	Free, forever

CLI Reference

scherlok connect <url>          Connect to a database
scherlok investigate            Profile all tables (learn patterns)
scherlok watch                  Detect anomalies and alert
scherlok status                 Quick health dashboard
scherlok report                 Detailed profile summary
scherlok history [--days N]     Timeline of past anomalies
scherlok config --store <url>   Set remote storage
scherlok version                Show version

Install

pip install scherlok

# With BigQuery support
pip install scherlok[bigquery]

Requires Python 3.10+.

Contributing

Contributions welcome! See CONTRIBUTING.md.

We're especially looking for:

• New database connectors (Snowflake, MySQL, DuckDB)
• Anomaly detection improvements
• Documentation and examples

License

MIT — Developed by Robson Bayer Müller