Duplicate code agent with jscpd

Why a CLI

A model reading a diff can’t know that the 30 lines it just read already exist three folders away. jscpd can: it scans the checkout and reports every clone with both locations. This agent runs it, keeps the clones the pull request introduced, and posts each one with jscpd’s own output as evidence. The example is a TypeScript billing service. Adjust paths and thresholds to your repository.

Step 1 — Create the agent

In Code review → What to review → Custom agents, click New agent → Templates → Blank. On its page, fill in Instructions:

Name

Duplicate code

Instructions

Find code this pull request adds or changes that duplicates code already in the repository.

Run jscpd on the directories the pull request changes, then read both copies of each clone it reports.

Report a clone only when:
- one of its copies is in a file this pull request changes, and
- both copies do the same thing (same logic, not just similar boilerplate), and
- the duplicated block is at least 10 lines.

Ignore tests, fixtures, migrations, generated code, imports and type declarations.

For each finding, name both locations and say what to extract or reuse: an existing function when one copy already is one, or a new shared helper otherwise.

Step 2 — Set the files

Under Files & knowledge:

Field	Value
Files	`src/**`
Except	`*/.test.ts`, `*/.spec.ts`, `/__fixtures__/`, `/generated/`, `src/db/migrations/**`

Step 3 — Add the CLI

Under Tools → CLIs, click Add CLI:

Field	Value
Name	`jscpd`
Binary	`jscpd`
Install	`npm i -g jscpd@5.4.1`
Allowed command prefixes	`jscpd --reporters console`
Allowed domains	(empty: jscpd needs no network)
Runs project code	Off: jscpd reads files, it doesn’t execute them
Secrets	(none)

Usage:

jscpd finds copy-pasted code across the repository.

Call it with the console reporter, the thresholds, and the directories the pull request changes:

--reporters console --min-lines 10 --min-tokens 70 --ignore **/*.test.ts,**/generated/** src/billing src/invoices

There is no shell: do not quote arguments. Each clone prints both copies as `path [startLine:col - endLine:col]`.
Read both copies before reporting a clone.

Step 4 — Comments

Under Comments & model:

Field	Value	Why
Format	Inline comments	Each clone lands on the copied lines.
Minimum severity	Team minimum
Max comments per pull request	`5`	A large copy-paste can produce many clones; the most severe are kept.
Suggested fix	Never	The fix is a refactor across files, not a line change.
How it writes	`Two sentences: where the other copy is, and what to reuse or extract.`

Click Save.

Step 5 — Try it

Paste the link of a pull request that copies a function, and click Run agent. Check:

Tool calls shows the jscpd call and its output.
Each kept finding’s Comment ends with an Evidence block quoting the jscpd lines that name the file:

**Evidence** (`jscpd`):
> - src/billing/invoice.ts [12:1 - 41:2] (29 lines, 212 tokens)
> src/billing/credit-note.ts [8:1 - 37:2]

If Warnings says the CLI could not be installed, check the install command. CLIs need the E2B sandbox; without it the agent runs without jscpd. Turn the agent on when the findings are the ones you want.

Checklist

Install pinned to an exact version
Allowed prefix starts with a flag, not just the binary
Tests and generated code in Except and in the jscpd --ignore
Max comments per pull request set
Tried on a pull request with a known copy

For every field, see Skills, docs and tools.

Custom Plugins

Custom Context Playbooks

Recipes

Custom Agents

LLM Provider Setup

Duplicate code agent with jscpd

Why a CLI

Step 1 — Create the agent

Step 2 — Set the files

Step 3 — Add the CLI

Step 4 — Comments

Step 5 — Try it

Checklist

​Why a CLI

​Step 1 — Create the agent

​Step 2 — Set the files

​Step 3 — Add the CLI

​Step 4 — Comments

​Step 5 — Try it

​Checklist

Why a CLI

Step 1 — Create the agent

Step 2 — Set the files

Step 3 — Add the CLI

Step 4 — Comments

Step 5 — Try it

Checklist