Introduction

What Geometer does#

An AI agent that issues refunds, sends emails or changes records is easy to test when everything works. The hard cases are the ones where something goes wrong in the middle: a payment service takes the money but its reply never arrives, a request is cut short, or a process crashes after half of a change. Agents often retry when they do not hear back, and a retry is how a customer gets refunded twice or emailed five times.

Geometer runs your agent on your own computer, inside containers, with outside services such as payments or email simulated, so nothing real is charged or sent. It runs the agent normally, then again with something going wrong on purpose, and it checks each run against your business rules.

• Find the problem. Geometer reads your project, works out what your agent can do and which rules apply, and tries the agent with a lost reply, a lost request, a partly applied call, a lost acknowledgement or a crash. When a rule breaks, you get a problem described by what happened to the customer or record, step by step.
• Replay it. Geometer repeats the problem exactly, from a clean start, so you can watch it and trust that it is real.
• Check your fix. After you change your code, Geometer replays the problem on the new code and tries a few nearby cases.
• Keep the check. A fixed problem can become a kept check, stored in your project, so geo ci runs it in your continuous integration from then on and the mistake cannot come back unnoticed.
• Earn authority. The evidence feeds an overview that shows what each action of your agent may do now and what would make it ready for more. A person grants each level, with a limit and a review date.
• Guard. Guard sits between your agent and its tools. It first only watches and records what it would have stopped. Later, if you decide, it stops calls that break your rules and holds large ones until a person approves them.
• Use it where you work. Your coding assistant can run checks and read problems through geo mcp serve, and geo mcp wrap puts a small relay in front of your MCP servers so you can try your agent against a simulated service. See Use Geometer from your coding assistant and Put Geometer in front of your MCP servers.
• Prove and certificates. Prove keeps a record of what Geometer checked and found. A certificate is a signed report of what was checked, what held, what broke and what was not checked, which you can hand to a reviewer.

Who it is for#

• Engineers building agents that act. Agents that move money, change records or contact customers, starting with refunds and payment exceptions. You get problems you can replay and checks that run in CI.
• The people who decide what an agent may do. Product, risk and engineering leads can read the overview, see what was and was not tried, and grant or limit authority without reading code.
• Reviewers and customers. A certificate and the open verifier let someone check a record without trusting Geometer.

The wording in the app and in these docs is meant for both engineers and non-engineers. Geometer reports what it found and what it did not check. A clean result means nothing broke in the runs that were tried, which is not a promise that nothing can.

Three ways to use it#

• The Mac app. A window with the whole workspace, for Apple silicon Macs. See Install.
• The terminal. The geo command on macOS and Linux. geo ci runs your kept checks in CI, and geo open opens the same workspace in your browser. See the command reference.
• The CI image. A Docker image that runs geo ci on Linux CI systems. See Run kept checks in CI.

All three share the same records on your computer. There is no account and no telemetry.

What the alpha is and is not#

This is 0.1.0-alpha.2, the second public alpha (the first, 0.1.0-alpha.1, came out on 24 October 2026). It has been run on Geometer's sample projects, on small agents Geometer wrote for each framework on Works with and on its own open agents, and has so far been used only by its own team. Expect rough edges, and please report what goes wrong.

Where to go next#

• Install GeometerDownload the app or the terminal build and get Docker ready.
• QuickstartCheck your own project, read a problem, fix it and keep the check, or learn on the practice project first.
• ConceptsThe words Geometer uses: rules, situations, problems, replay and kept checks.
• Command referenceEvery command, grouped as geo --help groups them.