GitLab Duo comparison for behavior checks before a merge request

Catch the fix an agent removes later.

A saved requirement makes a recurring mistake checkable. In this Perch capture from September 20, 2026, the same rule flags a missing guard and passes after the guard is restored.

def refund(order, payment):
    payment.refund(order.total)
    order.status = "refunded"
    return order

def refund(order, payment):
    if order.status == "refunded":
        return order
    payment.refund(order.total)
    order.status = "refunded"
    return order

Source: public order-service checkout.py at the linked commit. The captured standalone file is refund.py. Perch command output and timestamp. This saved-rule demonstration does not measure GitLab Duo Code Review Flow's detection rate.

Perch vs GitLab Duo Code Review Flow: what your team runs.

Perch turns project behavior into focused checks that agents can run before committing. Use these differences to choose the review workflow and billing model your team needs.

GitLab Duo comparison for behavior checks before a merge request

GitLab's managed on-demand review rate can be below Perch's mid-sized estimate. Perch adds a local semantic-rule workflow before the merge request: select a project requirement, check the edited file, and reuse the same rule in CI across Git providers.

Review before committing

GitLab Duo Code Review Flow: GitLab merge-request flow; standalone local review was not verified. GitLab Duo Code Review Flow workflow documentation.

Perch reads the current working file with perch check. For a known requirement, select its rule name and method instead of requesting another broad review. A local CLI describes where the command runs; Perch sends relevant source to hosted TypeSafe models for analysis.

How do saved requirements differ?

GitLab Duo Code Review Flow: Custom review instructions with repository context. GitLab Duo Code Review Flow rule documentation.

Perch stores English ensure rules in perch.yaml or .perch/rules/. Project, file and method scopes determine what is checked. Run the named check after an edit and after the repair; a rule finding can fail the command and a CI gate. Perch rules · Working-file checks.

What does the review bill depend on?

Compare GitLab Duo Code Review Flow's billing unit and Perch's usage estimate

Is the CLI open source and offline?

GitLab Duo Code Review Flow: Commercial agent platform feature. GitLab Duo Code Review Flow product or license source.

Perch’s CLI is MIT-licensed; hosted model inference is a separate paid service included in its published check rate. It does not run the model offline. Unchanged requests can reuse cached answers for free. Fresh judgments can vary, and a passing requirement check does not prove application correctness. Perch MIT license.

When does GitLab Duo Code Review Flow fit the workflow?

GitLab Duo Code Review Flow uses cross-file merge-request context. Its on-demand review rate can be below Perch’s mid-sized estimate; Perch’s distinction here is the local, separately selected requirement check.

Estimate the review bill

Perch and GitLab Duo Code Review Flow: pricing, allowances and workload calculator

Make the agent check its next edit.

npm install -g @lakeday/perch

perch rules add refund-once \
  --where refund.py --each method \
  --ensure "Refunded orders cannot be refunded again."

perch check refund.py::refund --rules refund-once

Use perch scan for repository code at Git HEAD and changed-code CI checks for pull requests. New model judgments can vary. Repeatability comes from cached answers for unchanged requests; a pass does not prove application correctness.