Dmytro Shevchenko

Code review with a blocker/major/minor severity rubric

Get an AI code review that sorts every finding into blocker, major, minor or nit, gives a triggering input for each and ends with a merge verdict.

At a glance

Best for: Solo developers without a reviewer, or teams wanting a first-pass review that separates real bugs from style opinions.
Tested on: Claude · Opus 5.5
You fill in: contextstackcode
You get: BLOCKER 1: any user can modify any cart (line 2) findById(req.params.id) never checks ownership. A logged-in user who posts to /cart/ /coupon… (full result below)

Prompt

Review this code as the senior reviewer on my team.

Context: {{context}}
Stack: {{stack}}
Code:
{{code}}

Classify every finding with this rubric:

• BLOCKER: wrong results, data loss, security hole, or a crash on a realistic input

• MAJOR: a bug on an edge case, missing error handling that will page someone, or a performance problem at our scale

• MINOR: readability, naming, small duplication

• NIT: pure preference. At most 3 of these.

For each finding give: severity, line reference, what goes wrong with a concrete input or sequence of events that triggers it, and the suggested change as code.

Rules:

• Order findings by severity.

• Don't comment on anything a linter or formatter would catch.

• Don't pad. If there are no blockers, say so plainly.

• If a finding depends on something you can't see (middleware, schema, config), say what you're assuming.

End with a one-line verdict (approve / approve with changes / request changes) and the single most important thing to fix first.

Fill in

{{context}}: What the code is for, scale, and anything a reviewer on your team would knowe.g. Checkout API for a D2C store, ~2k orders/day, MongoDB via Mongoose
{{stack}}: Language, framework and versionse.g. Node 22, Express 5, Mongoose 8
{{code}}: The code to review, pasted in fulle.g. The POST /cart/:id/coupon route handler

Example input

context: Checkout API for a D2C store, about 2,000 orders a day, MongoDB via Mongoose. Carts belong to logged-in users; auth middleware sets req.user.
stack: Node 22, Express 5, Mongoose 8
code:
```js
router.post("/cart/:id/coupon", requireAuth, async (req, res) => {
  const cart = await Cart.findById(req.params.id)
  const coupon = await Coupon.findOne({ code: req.body.code })

  if (coupon.expiresAt < Date.now()) {
    return res.status(400).json({ error: "Coupon expired" })
  }
  if (coupon.usedCount >= coupon.maxUses) {
    return res.status(400).json({ error: "Coupon fully redeemed" })
  }

  cart.discount = cart.subtotal * coupon.percent / 100
  cart.total = cart.subtotal - cart.discount
  coupon.usedCount++

  await coupon.save()
  await cart.save()
  res.json(cart)
})
```

1.3k0

Generated Outputs (1)

3 hours ago

Claude

Opus 5.5

3 hours ago

Generated Output

BLOCKER 1: any user can modify any cart (line 2)
findById(req.params.id) never checks ownership. A logged-in user who posts to /cart//coupon changes that cart's total, and the response returns the whole cart document.
`js
const cart = await Cart.findOne({ _id: req.params.id, user: req.user.id })
if (!cart) return res.status(404).json({ error: "Cart not found" })
`

BLOCKER 2: unknown coupon code crashes the handler (line 3–5)
{ "code": "TYPO10" } makes coupon null, and coupon.expiresAt throws a TypeError, which surfaces as a 500. Add if (!coupon) return res.status(400).json({ error: "Invalid coupon" }).

BLOCKER 3: maxUses can be exceeded under concurrency (lines 8–15)
Read, check, increment and save aren't atomic. When a coupon with 1 use left is shared in a WhatsApp group, ten simultaneous requests all read usedCount = 99 and all pass. Do the check and increment in one operation:
`js
const coupon = await Coupon.findOneAndUpdate(
{ code, expiresAt: { $gt: new Date() }, $expr: { $lt: ["$usedCount", "$maxUses"] } },
{ $inc: { usedCount: 1 } },
{ new: true }
)
`

MAJOR 1: uses are consumed on apply, not on purchase (line 15)
Applying the same coupon twice to one cart burns two uses, and abandoned carts burn uses forever. Record the coupon on the cart and increment usedCount when the order is placed, using the atomic update above.

MAJOR 2: coupon saved before cart (lines 17–18)
If cart.save() fails validation, the use is spent and the customer gets nothing. Once MAJOR 1 is fixed this goes away. Otherwise, wrap both in a transaction.

MAJOR 3: float money (line 12)
1299 * 15 / 100 = 194.85 is fine, but with paise stored as decimals you'll get values like 0.30000000000000004. Store amounts in minor units (integers) and Math.round the discount.

MINOR: codes are case- and whitespace-sensitive
" save10" fails. Normalize with String(req.body.code ?? "").trim().toUpperCase(), and store codes uppercase.

I'm assuming requireAuth rejects anonymous users and that Cart has a user field. If carts are keyed differently, adjust BLOCKER 1's filter.

Verdict: request changes. Fix the ownership check first. It's exploitable today by any logged-in customer.

Why it works

The rubric with definitions does the heavy lifting. "Blocker" means wrong results, data loss, security or a realistic crash, so the model can't inflate a naming issue or bury an IDOR under style notes. Requiring a concrete input that triggers each finding filters out vague warnings: each finding needs a real exploit or failure path. Capping nits at 3 and banning linter-level comments keeps the review short. The "say what you're assuming" line matters for route handlers, where auth and schema live elsewhere. The one-line verdict gives you a decision, not just a list.

When not to use it

Don't use it for large diffs spread across many files. The model only sees what you paste, so cross-file bugs slip through. A repo-aware agent or a proper PR review tool is better there. It's also no substitute for a human reviewer on security-critical code (auth, payments) that is about to ship. Treat it as the first pass, not the sign-off.

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