A best-practices guide for jscodeshift, a tool that automatically transforms JavaScript and TypeScript source code. It covers how to parse code, find syntax structures, change them, generate output, and test the transformations.

Use it when writing, debugging, reviewing, testing, or speeding up jscodeshift codemods for code migrations.

It helps prevent codemods—automated code migrations—from changing the wrong code or failing on less common cases.

jscodeshift — Skill for Claude Code and Codex by pproenca

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add pproenca/dot-skills --skill jscodeshift

Clone the repo

git clone --depth 1 https://github.com/pproenca/dot-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/pproenca/dot-skills/jscodeshift/github.svg)](https://agentmods.dev/skills/pproenca/dot-skills/jscodeshift)

Your own site

<a href="https://agentmods.dev/skills/pproenca/dot-skills/jscodeshift"><img src="https://agentmods.dev/badge/skills/pproenca/dot-skills/jscodeshift/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/pproenca/dot-skills/jscodeshift"><img src="https://agentmods.dev/badge/skills/pproenca/dot-skills/jscodeshift.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 61 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,574 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

Socket pass 18 Mar 2026
Snyk pass 16 Feb 2026
NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00061	$0.01574
Opus 5	$0.00030	$0.00787
Sonnet 5	$0.00012	$0.00315
Haiku 4.5	$0.00006	$0.00157

Measured 6d ago against content hash 3160ec06601e, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

jscodeshift scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/.experimental/jscodeshift/SKILL.md · 117 lines

How it starts

The opening of the file, as written. The whole thing — 117 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Facebook/Meta jscodeshift Best Practices

Comprehensive best practices guide for jscodeshift codemod development, designed for AI agents and LLMs. Contains 40 rules across 8 categories, prioritized by impact from critical (parser configuration, AST traversal) to incremental (advanced patterns). Each rule includes detailed explanations, real-world examples, and specific impact metrics.

When to Apply

Reference these guidelines when:

Writing new jscodeshift codemods for code migrations
Debugging transform failures or unexpected behavior
Optimizing codemod performance on large codebases
Reviewing codemod code for correctness
Testing codemods for edge cases and regressions

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Parser Configuration	CRITICAL	`parser-`
2	AST Traversal Patterns	CRITICAL	`traverse-`
3	Node Filtering	HIGH	`filter-`
4	AST Transformation	HIGH	`transform-`
5	Code Generation	MEDIUM	`codegen-`
6	Testing Strategies	MEDIUM	`test-`
7	Runner Optimization	LOW-MEDIUM	`runner-`
8	Advanced Patterns	LOW	`advanced-`

Quick Reference

1. Parser Configuration (CRITICAL)

parser-typescript-config - Use correct parser for TypeScript files
parser-flow-annotation - Use Flow parser for Flow-typed code
parser-babel5-compat - Avoid default babel5compat for modern syntax
parser-export-declaration - Export parser from transform module
parser-astexplorer-match - Match AST Explorer parser to jscodeshift parser

2. AST Traversal Patterns (CRITICAL)

traverse-find-specific-type - Use specific node types in find() calls
traverse-two-pass-pattern - Use two-pass pattern for complex transforms
traverse-early-return - Return early when no transformation needed
traverse-find-filter-pattern - Use find() with filter object over filter() chain
traverse-closest-scope - Use closestScope() for scope-aware transforms
traverse-avoid-repeated-find - Avoid repeated find() calls for same node type

Read the full file on GitHub · 117 lines

Files

What ships with it

45 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

6d ago First seen · 117 lines · 61 tokens per session scan A 3160ec06601e

Subscribe to this mod's changes

jscodeshift is a skill published in the GitHub repository pproenca/dot-skills (205 stars, last pushed 24d ago), licensed MIT. It adds 61 tokens to every session and 1,574 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

Languages Testing TypeScript

migrate-to-shoehorn

Migrate test files from as type assertions to @total-typescript/shoehorn. Use when user mentions shoehorn, wants to replace as in tests, or needs partial test data.

mattpocock/skills · 48 tokens

typescript-test-writing

Use this skill when writing or modifying tests in the llxprt-code repository. Covers mandatory TDD, behavioral testing, bun:test conventions and file naming, mock hygiene (no mock theater), and what never to test. Distilled from dev-docs/RULES.md, which remains the source of truth.

vybestack/llxprt-code · 66 tokens

jscodeshift