agentmods.dev

go-codemod

A guide for implementing and testing Go codemods used by the gh aw fix command. Codemods are small automated code transformations, in this case focused on YAML front matter.

In plain words
What is it for?
Use it when adding or updating a codemod, including its registry entry, metadata, precondition checks, transformation, and tests.
Why use it?
It defines the pipeline rules and safety checks needed so migrations apply only when appropriate and leave unrelated input unchanged.

Skill for Claude CodeCodex

5.0k 2d ago A scan 19 tokens original MIT
View the source file github/gh-aw
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.

agentmods
npx agentmods add skills/github/gh-aw/go-codemod
Any agent
npx skills add github/gh-aw --skill go-codemod
Clone the repo
git clone --depth 1 https://github.com/github/gh-aw

Made for: Claude Code, Codex.

Per session 19 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 906 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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.

ModelPer sessionOnce invoked
Fable 5 $0.00019 $0.00906
Opus 5 $0.00010 $0.00453
Sonnet 5 $0.00004 $0.00181
Haiku 4.5 $0.00002 $0.00091

Measured 2d ago against content hash 92ce93c1530d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

go-codemod 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 2d 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.

.github/skills/go-codemod/SKILL.md · 92 lines

How it starts

The opening of the file, as written. The whole thing — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Go Codemod Implementation Guide

Use this skill when adding or updating codemods used by gh aw fix.

Understand the fix pipeline first

  1. Review pkg/cli/fix_command.go to understand execution flow:
    • codemods are loaded once via GetAllCodemods()
    • each codemod is applied in registry order
    • frontmatter is re-parsed before each codemod
    • codemods must return (newContent, applied, error) and be safe for no-op input
  2. Review the codemod registry in pkg/cli/fix_codemods.go.
  3. Review helper utilities in pkg/cli/yaml_frontmatter_utils.go and reusable codemod helper constructors in pkg/cli/codemod_factory.go.

Implementation steps

  1. Create a new codemod file in pkg/cli/ named codemod_<feature>.go.
  2. Add a package logger with logger.New("cli:codemod_<feature>").
  3. Implement get<Feature>Codemod() Codemod and populate all metadata fields:
    • ID (stable, unique)
    • Name (human-readable)
    • Description (clear migration behavior)
    • IntroducedIn (release version)
  4. In Apply:
    • check frontmatter preconditions first
    • return unchanged content and applied=false when migration is not needed
    • transform only frontmatter using applyFrontmatterLineTransform from pkg/cli/yaml_frontmatter_utils.go
    • preserve comments/formatting/markdown body
    • avoid lossy rewrites and avoid touching unrelated keys
  5. Prefer existing helpers before writing custom parsing logic:
    • findAndReplaceInLine
    • removeFieldFromBlock
    • removeParentBlockIfTrulyEmpty
    • newFieldRemovalCodemod
    • newMoveTopLevelKeyToOnBlockCodemod
  6. If the codemod depends on external data or side effects, inject dependencies through a ...WithDeps constructor so tests can mock behavior.
  7. Register the codemod in pkg/cli/fix_codemods.go within GetAllCodemods().

Testing requirements

Create pkg/cli/codemod_<feature>_test.go and cover:

  1. Metadata correctness (ID, Name, Description, IntroducedIn, Apply != nil).
  2. Happy path migration with expected output.
  3. No-op behavior when deprecated input is absent.
  4. Idempotence behavior (already-migrated input remains unchanged).
  5. Preservation guarantees:
    • inline comments
    • indentation
    • markdown body after frontmatter
  6. Edge cases specific to the codemod (nested fields, mixed forms, ordering constraints, strict-mode checks, etc.).
  7. Dependency-injection behavior if ...WithDeps exists (success and fallback/error paths).

Read the full file on GitHub · 92 lines

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.

  1. 2d ago First seen · 92 lines · 19 tokens per session scan A 92ce93c1530d

Subscribe to this mod's changes

go-codemod is a skill published in the GitHub repository github/gh-aw (5,050 stars, last pushed 2d ago), licensed MIT. It adds 19 tokens to every session and 906 once invoked, about $0.0001 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 2026-08-30.

DevOps and cloudLanguagesTestingactionscaiciclaude-codecodexgh-extension
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