MergeSafe comparison for scope and custom behavior rules

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 MergeSafe's detection rate.

Perch vs MergeSafe: 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.

MergeSafe comparison for scope and custom behavior rules

MergeSafe Budget reviews cost less than Perch's mid-sized PR estimate. Choose Perch for independently selectable semantic requirements, uncommitted-file checks and a wider parsed-method scan scope. The value is making a project-specific correction repeatable in the agent's edit loop.

Review before committing

MergeSafe: GitHub app, API and agent-fix workflows; standalone CLI was not verified. MergeSafe 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?

MergeSafe: Reply-taught rules and repository allowlists. MergeSafe 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 MergeSafe's billing unit and Perch's usage estimate

Is the CLI open source and offline?

MergeSafe: Commercial review service. MergeSafe 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 MergeSafe fit the workflow?

MergeSafe Budget can cost less than Perch’s mid-sized example. Its review-size limits, optional experts and large-change multiplier make scope and required analysis more useful comparisons than a universal cheapest claim.

Estimate the review bill

Perch and MergeSafe: 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.