Implementation:Apache Druid Json Completion Engine

Knowledge Sources	Apache_Druid
Domains	Web_Console, Editor_Autocomplete
Last Updated	2026-02-10 10:00 GMT

Overview

Provides a rule-based JSON autocompletion engine for context-aware suggestions in JSON editors.

Description

The JSON Completion Engine module defines interfaces for completion rules and items, and exposes a function to resolve completions based on the current cursor path within a JSON document. Each rule specifies a path pattern (string or regex), an optional condition function evaluated against the current object context, and a list of completion items. The path system converts array indices to bracket notation (e.g., `$.aggregations[].type`) for pattern matching.

Usage

Used in the web console's JSON spec editors (e.g., ingestion spec editor) to provide intelligent autocompletion suggestions when editing Druid configuration JSON documents.

Code Reference

Source Location

• Repository: Apache Druid
• File: web-console/src/utils/json-completion.ts
• Lines: 1-84

Signature

export interface JsonCompletionRule {
  path: string | RegExp;
  isObject?: boolean;
  condition?: (currentObject: any) => boolean;
  completions: JsonCompletionItem[];
}

export interface JsonCompletionItem {
  value: string;
  documentation?: string;
}

export function getCompletionsForPath(
  rules: readonly JsonCompletionRule[],
  path: string[],
  isKey: boolean,
  currentObject: any,
): JsonCompletionItem[];

Import

import { getCompletionsForPath, JsonCompletionRule, JsonCompletionItem } from './utils/json-completion';

I/O Contract

Inputs

Name	Type	Required	Description
rules	readonly JsonCompletionRule[]	Yes	Array of completion rules defining paths and their available completions
path	string[]	Yes	The current cursor path as an array of JSON keys (e.g., ['aggregations', '0', 'type'])
isKey	boolean	Yes	Whether the cursor is at a key position (true) or value position (false)
currentObject	any	Yes	The current JSON object context for evaluating rule conditions

Outputs

Name	Type	Description
(return)	JsonCompletionItem[]	Array of matching completion items with value and optional documentation

Usage Examples

Define rules and get completions

import { getCompletionsForPath, JsonCompletionRule } from './utils/json-completion';

const rules: JsonCompletionRule[] = [
  {
    path: '$.aggregations.[].type',
    completions: [
      { value: 'count', documentation: 'Counts the number of rows' },
      { value: 'longSum', documentation: 'Sums a long column' },
    ],
  },
];

const items = getCompletionsForPath(
  rules,
  ['aggregations', '0', 'type'],
  false,
  { type: '' },
);
// Returns: [{ value: 'count', ... }, { value: 'longSum', ... }]

Related Pages

• Environment:Apache_Druid_Web_Console_Development