Context-Efficient Extraction

Extract specific data from files using CLI tools instead of built-in Read/Grep. Saves 80-95% of context tokens on large files and enables features the built-in tools lack.

Route by Task

| Task | Tool | When to use over built-in | |------|------|--------------------------| | JSON field extraction | jq | File >50 lines, need specific fields | | YAML field extraction | yq | File >50 lines, need specific fields | | Markdown element extraction | mq | Need code blocks, links, headers, tables | | Text search with advanced flags | rg | Need -F, -v, -w, -C, pipe composition |

Fall back to Read when the file is small (<50 lines), the overall structure matters, or edits follow immediately. Fall back to built-in Grep for straightforward pattern matching (handles 95% of search needs).

jq: JSON Extraction

# Specific field
jq -r '.version' package.json
jq -r '.compilerOptions.target' tsconfig.json

# Nested field
jq -r '.dependencies.react' package.json

# All keys at a level
jq -r '.scripts | keys[]' package.json
jq -r '.dependencies | keys[]' package.json

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

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

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

# Pluck from array
jq -r '.data[].name' response.json

# Filter with to_entries
jq -r '.dependencies | to_entries[] | select(.value | startswith("^")) | "\(.key): \(.value)"' package.json

Common files: package.json, tsconfig.json, package-lock.json, .eslintrc.json, API responses.

For detailed patterns (package.json, tsconfig, API responses), load jq reference.

yq: YAML Extraction

# Specific field
yq '.version' pubspec.yaml
yq '.services.web.image' docker-compose.yml

# All keys at a level
yq '.services | keys' docker-compose.yml

# Nested array element
yq '.jobs.build.steps[0].name' .github/workflows/ci.yml

# Filter by condition
yq '.services.[] | select(.ports)' docker-compose.yml

# Multiple fields
yq '.name, .version' pubspec.yaml

# Wildcard across siblings
yq '.services.*.image' docker-compose.yml

# Output as JSON
yq -o=json '.' config.yaml

Common files: docker-compose.yml, .github/workflows/*.yml, kubernetes manifests, Helm charts, pubspec.yaml.

For detailed patterns (Docker Compose, GitHub Actions, Kubernetes), load yq reference.

mq: Markdown Extraction

# Code blocks
mq '.code' README.md
mq '.code("python")' README.md

# Headers
mq '.h' README.md
mq '.h2' README.md

# Links
mq '.link.url' README.md

# Tables
mq '.[][]' README.md

# Lists
mq '.list' README.md

# YAML frontmatter
mq '.yaml.value' file.md

# Frontmatter parsed to JSON
mq '.yaml.value' file.md | yq -o json

# Filter by content
mq '.code | select(contains("import"))' file.md

# JSON output for further processing
mq -F json '.code' README.md | jq '.[0]'

Common files: README.md, CHANGELOG.md, documentation, API docs, specs.

For detailed patterns (selectors, filtering, output formats, frontmatter), load mq reference.

rg: Advanced Text Search

Use rg via Bash when the built-in Grep tool lacks the flag or composition needed.

# Fixed string (no regex interpretation)
rg -F 'console.log(' .

# Word boundaries
rg -w 'function' .

# Invert match
rg -v 'test' -t js .

# Context lines
rg -n -C 2 'pattern' .

# Specific file types
rg -t js 'import' .
rg -t py 'def ' .
rg -t go 'func ' .

# Exclude directories
rg --glob '!node_modules' 'pattern' .

# Count matches per file
rg -c 'TODO' .

# Files only (no content)
rg -l 'pattern' .

# Pipe composition
rg 'pattern' . | head -10
rg -l 'pattern' . | sort -u

For detailed patterns (function defs, imports, file types, pipe composition), load rg reference.

Cross-Tool Pipelines

# Parse markdown frontmatter as structured data
mq '.yaml.value' file.md | yq '.description'

# Markdown to JSON to jq
mq -F json '.link' README.md | jq '.[].url'

# Find files by content, extract structured data
rg -l 'apiVersion' -t yaml | xargs -I {} yq '.kind' {}

# Find markdown files, extract code blocks
fd -e md | xargs -I {} mq '.code("bash")' {}

# YAML to JSON conversion
yq -o=json '.' config.yaml | jq '.services | keys[]'

Core Principle

One command, exact data, minimal context. Built-in tools load everything; these tools load only what matters.