jq: JSON Query Tool

Extract specific fields from JSON files without reading entire contents into context.

When to Use

Use jq when:

• Need specific field(s) from JSON config
• File is large (>50 lines) and only need subset
• Querying nested structures
• Working with package.json, tsconfig.json, lock files, API responses

Just use Read when:

• File is small (<50 lines)
• Need to understand overall structure
• Making edits (need full context anyway)

Common Files

• package.json - dependencies, scripts, version
• tsconfig.json - compiler options
• package-lock.json - locked versions
• *.json API responses
• .eslintrc.json, prettierrc.json - tool configs

Quick Reference

# Get specific field
jq -r '.version' package.json
jq -r '.name' package.json

# Get nested field
jq -r '.dependencies.react' package.json
jq -r '.compilerOptions.target' tsconfig.json

# Get all keys
jq -r '.scripts | keys[]' package.json
jq -r '.dependencies | keys[]' package.json

# Get multiple fields
jq '{name, version}' package.json

# Filter array
jq '.items[] | select(.active == true)' data.json

# Count items
jq '.dependencies | length' package.json

package.json Patterns

# Version
jq -r '.version' package.json

# All scripts
jq '.scripts' package.json

# Specific script
jq -r '.scripts.build' package.json

# All dependencies (names only)
jq -r '.dependencies | keys[]' package.json

# Dependency version
jq -r '.dependencies["lodash"]' package.json

# Dev dependencies
jq -r '.devDependencies | keys[]' package.json

tsconfig.json Patterns

# Target
jq -r '.compilerOptions.target' tsconfig.json

# All compiler options
jq '.compilerOptions' tsconfig.json

# Include paths
jq '.include' tsconfig.json

# Strict mode
jq -r '.compilerOptions.strict' tsconfig.json

API Response Patterns

# Get data array
jq '.data' response.json

# First item
jq '.data[0]' response.json

# Pluck field from all items
jq '.data[].name' response.json

# Filter by condition
jq '.data[] | select(.status == "active")' response.json

# Count results
jq '.data | length' response.json

Core Principle

Extract exactly what's needed in one command. Saves 80-95% context vs reading entire JSON files.