Agent skill

jq

Use when processing JSON or YAML data from the command line. Covers jq for JSON and yq for YAML — filtering, transforming, and extracting data from structured outputs of APIs, config files, and CLI tools. USE FOR: jq, yq, JSON processing, YAML processing, CLI data transformation, filtering JSON, extracting fields, JSON to CSV, JSON arrays, jq expressions, yq expressions DO NOT USE FOR: general text processing (use grep/sed/awk via bash), XML processing, full programming (use Python or Node.js for complex transformations)

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Install this agent skill to your Project

npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/jq

Metadata

Additional technical details for this skill

author
Tyler-R-Kendrick
displayName
jq & Data Processing

SKILL.md

jq & Data Processing

Overview

jq is "sed for JSON" — a lightweight command-line processor for JSON data. Combined with curl, it's the standard way to interact with REST APIs from the terminal. yq extends the same idea to YAML.

Installation

Platform jq yq
Windows choco install jq / winget install jqlang.jq choco install yq
macOS brew install jq brew install yq
Linux apt install jq snap install yq

jq Basics

Identity (pretty-print)

bash
echo '{"name":"Alice","age":30}' | jq '.'

Field access

bash
echo '{"name":"Alice","address":{"city":"NYC"}}' | jq '.name'
# "Alice"

echo '{"name":"Alice","address":{"city":"NYC"}}' | jq '.address.city'
# "NYC"

Array indexing

bash
echo '[10,20,30,40,50]' | jq '.[0]'     # 10
echo '[10,20,30,40,50]' | jq '.[-1]'    # 50
echo '[10,20,30,40,50]' | jq '.[2:5]'   # [30,40,50]

Array iteration

bash
echo '[{"name":"Alice"},{"name":"Bob"}]' | jq '.[]'

Pipe

bash
curl -s https://api.example.com/data | jq '.users[] | .name'

Select / filter

bash
echo '[{"name":"Alice","age":35},{"name":"Bob","age":25}]' | jq '.[] | select(.age > 30)'

Map

bash
echo '[{"name":"Alice"},{"name":"Bob"}]' | jq '[.[] | .name]'
# ["Alice", "Bob"]

Keys, length, type

bash
echo '{"a":1,"b":2}' | jq 'keys'       # ["a","b"]
echo '[1,2,3]' | jq 'length'            # 3
echo '"hello"' | jq 'type'              # "string"

Construct objects

bash
echo '{"first":"Alice","contact":{"email":"[email protected]"}}' | jq '{name: .first, email: .contact.email}'

String interpolation

bash
echo '{"name":"Alice","email":"[email protected]"}' | jq '"\(.name) - \(.email)"'
# "Alice - [email protected]"

Common jq Recipes

Extract specific fields

bash
jq '.[] | {name, email}' users.json

Filter by value

bash
jq '[.[] | select(.status == "active")]' users.json

Count items

bash
jq '.users | length' data.json

Sort by field

bash
jq '.users | sort_by(.age)' data.json

Group by field

bash
jq '.users | group_by(.department)' data.json

Flatten arrays

bash
jq '[.[][]]' nested.json

JSON to CSV

bash
jq -r '.[] | [.name, .email, .age] | @csv' users.json

Unique values

bash
jq '[.[].category] | unique' items.json

Merge objects

bash
jq -s '.[0] * .[1]' defaults.json overrides.json

Conditional

bash
echo '{"age":21}' | jq 'if .age > 18 then "adult" else "minor" end'

yq Basics

Read a field

bash
yq '.metadata.name' deployment.yaml

Update a field

bash
yq '.spec.replicas = 3' -i deployment.yaml

Convert YAML to JSON

bash
yq -o json deployment.yaml

Convert JSON to YAML

bash
yq -P data.json

Merge YAML files

bash
yq eval-all '. as $item ireduce({}; . * $item)' base.yaml override.yaml

Combining with curl

bash
curl -s https://api.github.com/repos/torvalds/linux | jq '{name: .name, stars: .stargazers_count, language: .language}'

Output:

json
{
  "name": "linux",
  "stars": 178000,
  "language": "C"
}

Best Practices

  • Use jq for any JSON manipulation in shell scripts — it is purpose-built and reliable
  • Pipe curl -s to jq for API work — this is the standard pattern for CLI-based API interaction
  • Use yq for editing Kubernetes manifests, Helm values, and CI config files in place
  • Prefer jq over grep/awk for JSON — regex on JSON is fragile and error-prone
  • Use -r for raw string output in scripts to avoid quoted strings in downstream processing
  • Learn select() and map() — they handle the vast majority of filtering and transformation tasks

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