DRY Refactoring With jscpd

What it does

When your agent uses it

• Cleaning up duplicated code that jscpd reported
• Choosing where to start from a duplication hotspot summary
• Merging near-identical functions that differ only in names or values
• Extracting repeated blocks into shared functions or modules

Example prompts

• “Run jscpd on src and refactor the exact duplicates first.”
• “Which files have the highest duplication percentage? Start with those hotspots.”
• “These two functions are near-identical except for the endpoint; parameterize them.”
• “Extract the repeated validation block into a shared function.”

Requirements

• Node.js, to run jscpd through npx

Workflow steps

9 steps, taken from the first numbered list in SKILL.md.

1. 1Run jscpd with --reporters ai on the target path (add --summary on larger codebases to pick a starting point: files with high dup% and…
2. 2Parse each clone line to identify the two duplicated locations (file + line range) and its kind: no suffix is an exact copy, (renamed)…
3. 3Read both code fragments from the source files
4. 4Understand what the duplicated code does, and for renamed and similar clones list exactly what differs between the two sides
5. 5Triage renamed and similar clones before touching them. Skip the pair, and say so, when any of these holds: the two sides do different…
6. 6Design a refactoring: extract a shared function, class, module, or constant; the kind decides the strategy (below)
7. 7Apply the refactoring — update both locations and all other usages
8. 8Re-run jscpd with the same flags to confirm the clone is eliminated and the dup% of the touched files went down; a clone that was…
9. 9Repeat for remaining clones, highest-impact first: exact clones, then renamed, then similar. Report the skipped candidates separately from…

What it can do on your machine

Read from SKILL.md and the folder at commit 14bc176. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • npx

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md. Its commands use npx, which can reach the network depending on how they are called.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

DRY Refactoring With jscpd loads about 2.1k tokens when it runs. Until then it costs about 65 tokens; SKILL.md has 1,020 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~65

When it runs · the whole SKILL.md, loaded when a task matches

~2.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from kucherenko/jscpd at commit 14bc176, republished under its MIT licence (© kucherenko). 1,020 words, ~2,112 tokens.

name

dry-refactoring

description

Guided workflow to eliminate copy-paste duplication detected by jscpd. Refactor exact, renamed and near-miss clones using extract function, parameterize, module, constant, or base class strategies, starting from the hotspots the summary ranks.

npx jscpd --reporters ai <path>

npx jscpd --reporters ai --cross-formats "js-ts" <path>

npx jscpd --reporters ai --summary <path>

# Type-2: renamed copies (other variable names, other constants), reported as "(renamed)".
# Raise --min-tokens: with identifiers ignored, a short block is mostly placeholders.
npx jscpd --reporters ai --ignore-identifiers --min-tokens 70 <path>

# Type-3: near-miss copies (one or two edited lines, or JS/TS/Python functions with the same structure),
# reported as "[~0.91 gap]" and "[~0.85 ast]". Widen only if the tight run finds nothing.
npx jscpd --reporters ai --max-gap-lines 1 --similarity <path>

// Before: same block in two places
// After: shared function called from both places

// Move shared logic to a shared utility file and import it

// Before: computeCartTotal(items) and computeBasketTotal(entries), same body, other names;
//         limits-dev.js and limits-prod.js, same shape, other numbers
// After: one function whose parameters are the identifiers that differed,
//        or one function reading the values that differed from a config object

// Before: saveUser and saveAccount, identical except one inserted validation line
// After: one saveRecord(record, { validate }) with the inserted line behind the option,
//        or the inserted line moved to the caller before the shared call

// Before: buildInvoice(order, customer, taxRate) and buildCreditNote(refund, account, vatRate):
//         same loop, same rounding, one extra guard and one extra log call in the second
// After: buildDocument(source, party, rate, { filter, onBuilt }) used by both

© kucherenko, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/dry-refactoring of kucherenko/jscpd.

Open the folder on GitHubat commit 14bc176