chkit — ClickHouse Schema & Migration Toolkit

chkit lets you define ClickHouse schemas in TypeScript, generate migrations automatically, detect drift, and run CI checks from a single CLI.

Docs: https://chkit.obsessiondb.com

Configuration

All chkit projects have a clickhouse.config.ts at the project root:

import { defineConfig } from '@chkit/core'

export default defineConfig({
  schema: './src/db/schema/**/*.ts',    // Glob to schema files
  outDir: './chkit',                     // Artifact root
  migrationsDir: './chkit/migrations',   // SQL migration files
  metaDir: './chkit/meta',               // snapshot.json, journal.json
  plugins: [],                           // Plugin registrations
  clickhouse: {
    url: process.env.CLICKHOUSE_URL ?? 'http://localhost:8123',
    username: process.env.CLICKHOUSE_USER ?? 'default',
    password: process.env.CLICKHOUSE_PASSWORD ?? '',
    database: process.env.CLICKHOUSE_DB ?? 'default',
  },
  check: {
    failOnPending: true,
    failOnChecksumMismatch: true,
    failOnDrift: true,
  },
  safety: {
    allowDestructive: false,
  },
})

Schema DSL

Schema files are TypeScript files that export definitions using functions from @chkit/core.

Tables

import { schema, table } from '@chkit/core'

const events = table({
  database: 'default',
  name: 'events',
  columns: [
    { name: 'id', type: 'UInt64' },
    { name: 'org_id', type: 'String' },
    { name: 'source', type: 'LowCardinality(String)' },
    { name: 'payload', type: 'String', nullable: true },
    { name: 'received_at', type: 'DateTime64(3)', default: 'fn:now64(3)' },
    { name: 'status', type: 'String', default: 'pending', comment: 'Processing status' },
  ],
  engine: 'MergeTree()',
  primaryKey: ['id'],
  orderBy: ['org_id', 'received_at', 'id'],
  partitionBy: 'toYYYYMM(received_at)',
  ttl: 'received_at + INTERVAL 90 DAY',
  settings: { index_granularity: 8192 },
  indexes: [
    { name: 'idx_source', expression: 'source', type: 'set', typeArgs: '0', granularity: 1 },
  ],
})

export default schema(events)

Required table fields: database, name, columns, engine, primaryKey, orderBy. Optional: partitionBy, uniqueKey, ttl, settings, indexes, projections, comment, renamedFrom.

Column defaults

String values are single-quoted: default: 'pending' → DEFAULT 'pending'
Numbers are literal: default: 0 → DEFAULT 0
Function calls use fn: prefix: default: 'fn:now64(3)' → DEFAULT now64(3)

Views

import { view } from '@chkit/core'

const activeUsers = view({
  database: 'app',
  name: 'active_users',
  as: 'SELECT id, email FROM app.users WHERE active = 1',
})

Materialized views

import { materializedView } from '@chkit/core'

const eventCounts = materializedView({
  database: 'analytics',
  name: 'event_counts_mv',
  to: { database: 'analytics', name: 'event_counts' },
  as: 'SELECT org_id, count() AS total FROM analytics.events GROUP BY org_id',
})

Exporting

Use schema() to group definitions, or export individually (any export with a valid kind is discovered):

export default schema(users, events, eventCounts)
// or
export const users = table({ ... })
export const events = table({ ... })

CLI Commands

All commands support --json for machine-readable output and --config <path> for custom config files.

init — Scaffold project

chkit init

Creates clickhouse.config.ts and src/db/schema/example.ts.

generate — Create migrations

chkit generate --name add-users-table
chkit generate --dryrun                        # Preview without writing
chkit generate --table analytics.events        # Scope to specific table
chkit generate --rename-table old.users=new.accounts
chkit generate --rename-column db.table.old=new

Diffs schema definitions against the last snapshot. Each operation gets a risk level:

safe: CREATE TABLE, ADD COLUMN
caution: settings changes
danger: DROP TABLE, DROP COLUMN

migrate — Apply migrations

chkit migrate                  # Preview pending
chkit migrate --apply          # Apply all pending
chkit migrate --apply --allow-destructive   # Allow danger operations
chkit migrate --apply --table analytics.events

Verifies checksums before applying. Destructive operations require explicit --allow-destructive in CI.

status — Migration state

chkit status
# Output: Migrations: 5 total, 3 applied, 2 pending

Read-only, no ClickHouse connection needed.

drift — Compare live vs expected

chkit drift
chkit drift --table analytics.events

Compares snapshot against live ClickHouse. Reports missing/extra objects and column-level differences.

check — CI gate

chkit check              # Run all policy checks
chkit check --strict     # Force all policies on
chkit check --json       # Machine-readable output

Evaluates: pending migrations, checksum mismatches, schema drift, plugin checks. Exit code 1 on failure.

Rename Workflow

To rename a table or column without drop+recreate:

Table rename — set renamedFrom on the table:

const accounts = table({
  database: 'app',
  name: 'accounts',           // new name
  renamedFrom: { name: 'users' },  // old name
  // ... columns, engine, etc.
})

Column rename — set renamedFrom on the column:

columns: [
  { name: 'user_email', type: 'String', renamedFrom: 'email' },
]

CLI flags override schema metadata: --rename-table old=new, --rename-column db.table.old=new.

Plugins

import { codegen } from '@chkit/plugin-codegen'

export default defineConfig({
  plugins: [
    codegen({ outFile: './src/generated/chkit-types.ts', emitZod: true }),
  ],
})

Available plugins

Plugin	Install	Command	Purpose
`@chkit/plugin-codegen`	`bun add -d @chkit/plugin-codegen`	`chkit codegen`	Generate TypeScript types + Zod schemas
`@chkit/plugin-pull`	`bun add -d @chkit/plugin-pull`	`chkit pull`	Introspect live ClickHouse into schema files
`@chkit/plugin-backfill`	`bun add -d @chkit/plugin-backfill`	`chkit backfill`	Time-windowed data backfill with checkpoints

Common Workflows

New project

bun add -d chkit
bunx chkit init
# Edit src/db/schema/example.ts with your tables
bunx chkit generate --name init
bunx chkit migrate --apply

Add a table

Create a new schema file in src/db/schema/
Define the table using table() and export via schema()
Run chkit generate --name add-my-table
Run chkit migrate --apply

CI pipeline

chkit check --strict --json
# Fails if: pending migrations, checksum mismatches, schema drift, or plugin errors

Structural vs Alterable Properties

When a property changes, chkit determines whether ALTER or DROP+CREATE is needed:

Structural (requires drop+recreate): engine, primaryKey, orderBy, partitionBy, uniqueKey
Alterable (ALTER in place): columns, indexes, projections, settings, TTL, comment

Views and materialized views always use drop+recreate.

Documentation

Full documentation is at https://chkit.obsessiondb.com. The site supports content negotiation — request any page with Accept: text/markdown to receive raw source markdown instead of HTML. Fetch docs for details not covered in this skill file.

curl -s -H "Accept: text/markdown" <url>

Key pages

Page	URL	Use when
Schema DSL Reference	`https://chkit.obsessiondb.com/schema/dsl-reference/`	Full field specs, column types, validation rules
Configuration	`https://chkit.obsessiondb.com/configuration/overview/`	All config options and defaults
Codegen Plugin	`https://chkit.obsessiondb.com/plugins/codegen/`	TypeScript types, Zod schemas, ingest functions
Pull Plugin	`https://chkit.obsessiondb.com/plugins/pull/`	Introspecting live ClickHouse into schema files
Backfill Plugin	`https://chkit.obsessiondb.com/plugins/backfill/`	Time-windowed data backfill with checkpoints
CI/CD Integration	`https://chkit.obsessiondb.com/guides/ci-cd/`	Pipeline setup, check commands, deployment

Discover all pages

Fetch the index to find CLI command pages and any other documentation:

curl -s -H "Accept: text/markdown" https://chkit.obsessiondb.com/