explore-data

SKILL.md

/explore-data - Profile and Explore a Dataset

If you see unfamiliar placeholders or need to check which tools are connected, see CONNECTORS.md.

Generate a comprehensive data profile for a table or uploaded file. Understand its shape, quality, and patterns before diving into analysis.

Usage

/explore-data <table_name or file>

Workflow

1. Access the Data

If a data warehouse MCP server is connected:

Resolve the table name (handle schema prefixes, suggest matches if ambiguous)

Query table metadata: column names, types, descriptions if available

Run profiling queries against the live data

If a file is provided (CSV, Excel, Parquet, JSON):

Read the file and load into a working dataset

Infer column types from the data

If neither:

Ask the user to provide a table name (with their warehouse connected) or upload a file

If they describe a table schema, provide guidance on what profiling queries to run

2. Understand Structure

Before analyzing any data, understand its structure:

Table-level questions:

How many rows and columns?

What is the grain (one row per what)?

What is the primary key? Is it unique?

When was the data last updated?

How far back does the data go?

Column classification — categorize each column as one of:

Identifier: Unique keys, foreign keys, entity IDs

Dimension: Categorical attributes for grouping/filtering (status, type, region, category)

Metric: Quantitative values for measurement (revenue, count, duration, score)

Temporal: Dates and timestamps (created_at, updated_at, event_date)

Text: Free-form text fields (description, notes, name)

Boolean: True/false flags

Structural: JSON, arrays, nested structures

3. Generate Data Profile

Run the following profiling checks:

Table-level metrics:

Total row count

Column count and types breakdown

Approximate table size (if available from metadata)

Date range coverage (min/max of date columns)

All columns:

Null count and null rate

Distinct count and cardinality ratio (distinct / total)

Most common values (top 5-10 with frequencies)

Least common values (bottom 5 to spot anomalies)

Numeric columns (metrics):

min, max, mean, median (p50)
standard deviation
percentiles: p1, p5, p25, p75, p95, p99
zero count
negative count (if unexpected)

String columns (dimensions, text):

min length, max length, avg length
empty string count
pattern analysis (do values follow a format?)
case consistency (all upper, all lower, mixed?)
leading/trailing whitespace count

Date/timestamp columns:

min date, max date
null dates
future dates (if unexpected)
distribution by month/week
gaps in time series

Boolean columns:

true count, false count, null count
true rate

Present the profile as a clean summary table, grouped by column type (dimensions, metrics, dates, IDs).

4. Identify Data Quality Issues

Apply the quality assessment framework below. Flag potential problems:

High null rates: Columns with >5% nulls (warn), >20% nulls (alert)

Low cardinality surprises: Columns that should be high-cardinality but aren't (e.g., a "user_id" with only 50 distinct values)

High cardinality surprises: Columns that should be categorical but have too many distinct values

Suspicious values: Negative amounts where only positive expected, future dates in historical data, obviously placeholder values (e.g., "N/A", "TBD", "test", "999999")

Duplicate detection: Check if there's a natural key and whether it has duplicates

Distribution skew: Extremely skewed numeric distributions that could affect averages

Encoding issues: Mixed case in categorical fields, trailing whitespace, inconsistent formats

5. Discover Relationships and Patterns

After profiling individual columns:

Foreign key candidates: ID columns that might link to other tables

Hierarchies: Columns that form natural drill-down paths (country > state > city)

Correlations: Numeric columns that move together

Derived columns: Columns that appear to be computed from others

Redundant columns: Columns with identical or near-identical information

6. Suggest Interesting Dimensions and Metrics

Based on the column profile, recommend:

Best dimension columns for slicing data (categorical columns with reasonable cardinality, 3-50 values)

Key metric columns for measurement (numeric columns with meaningful distributions)

Time columns suitable for trend analysis

Natural groupings or hierarchies apparent in the data

Potential join keys linking to other tables (ID columns, foreign keys)

7. Recommend Follow-Up Analyses

Suggest 3-5 specific analyses the user could run next:

"Trend analysis on [metric] by [time_column] grouped by [dimension]"

"Distribution deep-dive on [skewed_column] to understand outliers"

"Data quality investigation on [problematic_column]"

"Correlation analysis between [metric_a] and [metric_b]"

"Cohort analysis using [date_column] and [status_column]"

Output Format

## Data Profile: [table_name]

### Overview
- Rows: 2,340,891
- Columns: 23 (8 dimensions, 6 metrics, 4 dates, 5 IDs)
- Date range: 2021-03-15 to 2024-01-22

### Column Details
[summary table]

### Data Quality Issues
[flagged issues with severity]

### Recommended Explorations
[numbered list of suggested follow-up analyses]

Quality Assessment Framework

Completeness Score

Rate each column:

Complete (>99% non-null): Green

Mostly complete (95-99%): Yellow -- investigate the nulls

Incomplete (80-95%): Orange -- understand why and whether it matters

Sparse (<80%): Red -- may not be usable without imputation

Consistency Checks

Look for:

Value format inconsistency: Same concept represented differently ("USA", "US", "United States", "us")

Type inconsistency: Numbers stored as strings, dates in various formats

Referential integrity: Foreign keys that don't match any parent record

Business rule violations: Negative quantities, end dates before start dates, percentages > 100

Cross-column consistency: Status = "completed" but completed_at is null

Accuracy Indicators

Red flags that suggest accuracy issues:

Placeholder values: 0, -1, 999999, "N/A", "TBD", "test", "xxx"

Default values: Suspiciously high frequency of a single value

Stale data: Updated_at shows no recent changes in an active system

Impossible values: Ages > 150, dates in the far future, negative durations

Round number bias: All values ending in 0 or 5 (suggests estimation, not measurement)

Timeliness Assessment

When was the table last updated?

What is the expected update frequency?

Is there a lag between event time and load time?

Are there gaps in the time series?

Pattern Discovery Techniques

Distribution Analysis

For numeric columns, characterize the distribution:

Normal: Mean and median are close, bell-shaped

Skewed right: Long tail of high values (common for revenue, session duration)

Skewed left: Long tail of low values (less common)

Bimodal: Two peaks (suggests two distinct populations)

Power law: Few very large values, many small ones (common for user activity)

Uniform: Roughly equal frequency across range (often synthetic or random)

Temporal Patterns

For time series data, look for:

Trend: Sustained upward or downward movement

Seasonality: Repeating patterns (weekly, monthly, quarterly, annual)

Day-of-week effects: Weekday vs. weekend differences

Holiday effects: Drops or spikes around known holidays

Change points: Sudden shifts in level or trend

Anomalies: Individual data points that break the pattern

Segmentation Discovery

Identify natural segments by:

Finding categorical columns with 3-20 distinct values

Comparing metric distributions across segment values

Looking for segments with significantly different behavior

Testing whether segments are homogeneous or contain sub-segments

Correlation Exploration

Between numeric columns:

Compute correlation matrix for all metric pairs

Flag strong correlations (|r| > 0.7) for investigation

Note: Correlation does not imply causation -- flag this explicitly

Check for non-linear relationships (e.g., quadratic, logarithmic)

Schema Understanding and Documentation

Schema Documentation Template

When documenting a dataset for team use:

## Table: [schema.table_name]

**Description**: [What this table represents]
**Grain**: [One row per...]
**Primary Key**: [column(s)]
**Row Count**: [approximate, with date]
**Update Frequency**: [real-time / hourly / daily / weekly]
**Owner**: [team or person responsible]

### Key Columns

| Column | Type | Description | Example Values | Notes |
|--------|------|-------------|----------------|-------|
| user_id | STRING | Unique user identifier | "usr_abc123" | FK to users.id |
| event_type | STRING | Type of event | "click", "view", "purchase" | 15 distinct values |
| revenue | DECIMAL | Transaction revenue in USD | 29.99, 149.00 | Null for non-purchase events |
| created_at | TIMESTAMP | When the event occurred | 2024-01-15 14:23:01 | Partitioned on this column |

### Relationships
- Joins to `users` on `user_id`
- Joins to `products` on `product_id`
- Parent of `event_details` (1:many on event_id)

### Known Issues
- [List any known data quality issues]
- [Note any gotchas for analysts]

### Common Query Patterns
- [Typical use cases for this table]

Schema Exploration Queries

When connected to a data warehouse, use these patterns to discover schema:

-- List all tables in a schema (PostgreSQL)
SELECT table_name, table_type
FROM information_schema.tables
WHERE table_schema = 'public'
ORDER BY table_name;

-- Column details (PostgreSQL)
SELECT column_name, data_type, is_nullable, column_default
FROM information_schema.columns
WHERE table_name = 'my_table'
ORDER BY ordinal_position;

-- Table sizes (PostgreSQL)
SELECT relname, pg_size_pretty(pg_total_relation_size(relid))
FROM pg_catalog.pg_statio_user_tables
ORDER BY pg_total_relation_size(relid) DESC;

-- Row counts for all tables (general pattern)
-- Run per-table: SELECT COUNT(*) FROM table_name

Lineage and Dependencies

When exploring an unfamiliar data environment:

Start with the "output" tables (what reports or dashboards consume)

Trace upstream: What tables feed into them?

Identify raw/staging/mart layers

Map the transformation chain from raw data to analytical tables

Note where data is enriched, filtered, or aggregated

Tips

For very large tables (100M+ rows), profiling queries use sampling by default -- mention if you need exact counts

If exploring a new dataset for the first time, this command gives you the lay of the land before writing specific queries

The quality flags are heuristic -- not every flag is a real problem, but each is worth a quick look

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