--- title: "Your coding agent writes the tests and runs them." description: "Connect Cursor, Claude Code or Codex to Momentic's MCP server. Agents write YAML tests into your repo, run them in a real browser, and investigate failures." canonical: "https://momentic.ai/coding-agents" last-updated: "2026-09-13T12:56:02-07:00" --- # Your coding agent writes the tests and runs them. URL: https://momentic.ai/coding-agents platform / coding-agents Momentic ships a local MCP server. Cursor, Claude Code and Codex call it to open a browser, build a test step by step, save the YAML in your repo, and read the failure back. [Try for free](https://app.momentic.ai/signup) [Get a demo](/sales) Cursor · Claude Code · Codex · OpenCode · GitHub Copilot ## Agents at work in real repositories. 117,010 bugs caught before deploy 70M+ Test runs executed 8.9M+ Steps auto-healed 80k+ PRs verified 339k+ Changes verified ## How an agent uses Momentic. The agent registers one local server, reads the skills that tell it how to test, then builds the test in a real browser and leaves the YAML in your repo. 01 ### Register the server Momentic runs as a local MCP server. Claude Code, Codex, and Cursor register it in one line, and mobile agents use the same server. 02 ### Install the skills One command installs the Momentic skills. They tell the agent how to build a test, how to write the affected tests before a change, and how to investigate a failure. 03 ### The agent writes and runs the test It drives a live browser, saves the YAML in your repo, runs it, and reads the result. The test change arrives in a pull request, and CI runs it on the next commit. ## What the MCP server exposes. The agent calls Momentic tools over a local stdio server, follows the skills that tell it how to test, and leaves a YAML file you review. ### Tests built against a live browser The momentic-test tools let an agent open your app, try a step, look at the result, and keep the step only when it works. The agent sees the real page before it saves a step. ### Executable specs before the code With momentic-spec, the agent writes the affected tests before it changes user-visible behavior, so the implementation has something to satisfy. The agent writes the check first, then makes it pass. ### Failure investigation with evidence momentic-maintain finds the runs for a branch, reads the saved classifications and run evidence, and points at the first run where behavior changed. The agent reads the run history before it edits a test. ### Web, iOS and Android momentic-mobile mcp gives an agent the same tools against iOS simulators and Android emulators, with the same YAML format. Same format on all three platforms. ### Runs on your machine The server is local stdio. It reads momentic.config.yaml in your project and uses the MOMENTIC_API_KEY you give the editor. The server talks to the project on your disk. ### The output is a file you review Every test an agent writes is YAML in your repo, so it goes through code review and the CLI runs it in CI. Agent work lands in a pull request. Engineering teams that let agents keep the tests current. Engineers stay in the editor, and the tests still land in the repo with the code change. “Momentic gave us a fast and reliable way to validate Poe.com's AI responses, even when they weren't deterministic.” Momoko F. Head of Product Operations, Quora 30 min daily test execution, down from 7 hours 500+ manual test cases replaced 100% critical tests created in one month [30 min daily test execution, down from 7 hours "Momentic gave us a fast and reliable way to validate Poe.com's AI responses, even when they weren't deterministic." Momoko F. Head of Product Operations, Quora](/customers/quora) [8x increase in release cadence "It's like giving someone your QA checklist and watching them execute it for you!" Sriram S. Engineering Lead, Source Control, Retool](/customers/retool) [80% faster release cycles "With Momentic, we've caught bugs that would have eluded even our most diligent internal tests." Alex C. CTO, GPTZero](/customers/gptzero) [6x faster end-to-end test creation "We've already seen a 30% decrease in production incidents thanks to Momentic's automated testing." Hanna K. Head of QA, CoverGo](/customers/covergo) [85% reduction in production incidents "Momentic gives us reliable end-to-end coverage, so we can focus on features instead of maintaining tests." Alec H. Staff AI Engineer, Mutiny](/customers/mutiny) [Browse all](/customers) ## Available across every platform. The same MCP tools and the same YAML on all three. [01 Web End-to-end browser testing on Chromium and Chrome.](/web-app-testing)[02 iOS Native iOS apps and SwiftUI, on hosted or local simulators.](/ios-testing)[03 Android Reliable Android tests on local or remote emulators in minutes.](/android-testing) ## Coding agents, answered. What is the Momentic MCP server? A local stdio server that exposes Momentic as tools a coding agent can call. The agent can open a browser, create and edit tests, run them, and read run history. Which agents work with it? Cursor, Claude Code, Codex, Devin, OpenCode and GitHub Copilot. Each one registers a stdio server that runs npx momentic mcp. How do I set it up in Claude Code? Run claude mcp add --transport stdio momentic -- npx momentic mcp --config /absolute/path/to/momentic.config.yaml, restart Claude Code, then run /mcp to confirm the server is active. What are Momentic skills? Markdown instructions that tell the agent how to use the tools. momentic-test builds tests, momentic-spec writes the affected tests before a product change, and momentic-maintain investigates failures. Install them with npx skills add momentic-ai/skills. Does the agent need an API key? Yes. Most editors do not inherit your shell environment, so set MOMENTIC_API_KEY in the MCP entry or start the editor from a shell that exports it. Where does the agent save the test? As a YAML file in your repo, next to your code. You review it in a pull request. Can the agent run the test it just wrote? Yes, through the same server, in a real browser. The CLI runs that same file in CI later. Our coding agent already runs our Playwright suite. What changes? Your agent stops maintaining the runner. Momentic re-resolves a moved locator and retries a transient obstruction inside the run, and MCP returns the failing step with its evidence. The [build vs buy calculator](/comparison/momentic-vs-build-your-own) prices the suite your agent keeps. Is that cheaper than having the agent maintain a Playwright suite? Yes. The run repairs transient failures, classifies the cause, and updates the test when it can. Your agent starts at the failing step for a real product failure, so it spends fewer cycles on test maintenance. What does the agent get back when a test fails? The failing step and its evidence: before and after screenshots, a DOM trace, network requests, console output, execution order, and video when recording is on. momentic-maintain also reads branch run history to find where behavior changed. Does the agent remember how our product works? Momentic keeps a Knowledge base of your terminology, your rules for agents, and your known flows, and Memory keeps the decisions from past runs. Every AI step retrieves the relevant entries, so a new session starts with product context. Does this replace the visual editor? No. The editor writes the same YAML, so one suite can hold tests from engineers, agents and the editor. Which CLI version do I need? Momentic CLI 2.54.0 or later. What is the difference between Playwright MCP and Momentic's MCP server? Playwright MCP drives a browser and writes Playwright code, so authoring-time selectors and strings become the test. Momentic previews each step on the live page, saves working steps as YAML, and replays them with step caching and auto-heal. Can an agent run tests and read the results over MCP? Yes. The agent runs a test through the same server, and the momentic-maintain skill reads the run history, the saved classifications and the step evidence for a branch. Does MCP keep our tests in version control? Yes. The agent writes a YAML file into your repo, so a test change arrives in a pull request and CI runs it on the next commit. Can a coding agent run tests in CI over MCP? No, and it does not need to. MCP is a local server for your editor. CI runs npx momentic run, and the exit code gates the merge. Still have additional questions? ## Close the feedback loop. Start for free, or book a demo and we'll run it against your app. [Try for free](https://app.momentic.ai/signup) [Get a demo](/sales)