Testing Tool

Regression Detector

Compare test results between runs to catch regressions before they ship. Identify new failures, fixed tests, and diff API response snapshots.

Install

Get the CLI Tool

Run the regression detector locally as an MCP server, or try it online below.

npx @clinetools/regression
Requires Node.js 18+
  • Compares before/after test results to detect new failures
  • Identifies regressions, fixes, new tests, and removed tests
  • Deep-diffs API response snapshots with path-level detail
  • Severity assessment from none to critical
  • Zero config — just run with npx
Tutorial

How to Use It

Three ways to detect regressions — pick the one that fits your workflow.

1

Try Online

Use the interactive demo below to compare test results — no install needed.

↓ Jump to interactive demo
2

Use via CLI

Run as a local MCP server and connect any MCP-compatible client.

npx @clinetools/regression
3

Add to AI Agent

Add the tool to your MCP settings for instant regression detection from your AI assistant.

"regression": { "command": "npx", "args": ["@clinetools/regression"] }

MCP Client Configuration (Cline)

{
  "mcpServers": {
    "regression": {
      "command": "npx",
      "args": ["@clinetools/regression"]
    }
  }
}

Claude Code Configuration

# In your project's .mcp.json:
{
  "mcpServers": {
    "regression": {
      "command": "npx",
      "args": ["@clinetools/regression"]
    }
  }
}

Example Prompt: Detect Regressions After Refactor

// Prompt to your AI agent:
"Compare the test results from before and after my refactor"

// The agent calls:
detect_regressions({
  before: '[{"name":"auth login","status":"pass"}, ...]',
  after: '[{"name":"auth login","status":"fail","error":"timeout"}, ...]'
})
// Returns detailed regression report with severity
Live Demo

Try It Online

Compare before and after test results to find regressions instantly.

Test Result Comparison

Paste baseline and current test results as JSON arrays

Try a demo:

Paste test results and click Detect Regressions to compare runs.

Details

Learn

Understanding Regressions

Why regressions happen and how to prevent them from reaching production.

Why Regressions Happen

Regressions occur when new code changes break existing functionality. Common causes include refactors that miss edge cases, dependency updates with breaking changes, merge conflicts resolved incorrectly, and shared state mutations. Automated detection catches them before users do.

CI/CD Integration

Run regression detection in your CI pipeline after every test suite execution. Compare against the last passing baseline to instantly flag new failures. Block merges when regressions are detected and require explicit sign-off to proceed.

Snapshot Testing

Capture API response snapshots and compare them between deploys. Detect added, removed, or changed fields with exact path-level detail. Use ignore paths for dynamic fields like timestamps and request IDs that change every run.

Regression Prevention

Write focused unit tests for every bug fix to prevent the same regression twice. Maintain a stable baseline of test results. Use feature flags to isolate changes. Run the full test suite before merging and monitor test stability trends over time.

Never Ship a Regression

Add the Regression Detector to your agent's toolkit and catch test failures before they reach production.

View Plans