The self-improvingharness for your construction projects

Your supers, PMs and project engineers take photos and use the app. 3PT is a self-improving harness. It learns how each role works, builds the next feature, ships it and scores it. A version that does worse rolls back. Every version is a checkpoint in MongoDB Atlas.

The demo firm is simulated with a fixed seed. The loop, the checkpoints and the policy rollback are real code.

ACME BUILDERSHarness v6
Unit 206 · plumbing · open wall
New for you

Your OAC photo pack, in one tap

Your team built the owner-architect-contractor photo pack by hand every Friday: 28 hours a job. I built it from this week's photos and turned it on.

Example feature from the simulated firm
On the job

Software that learns your jobsite, then ships.

No settings screen and no ticket to IT. Your crew does the job. The harness learns the job and keeps only what helps.

  1. 1 · YOUR CREW WORKSPhotos, searches, owner updates

    Supers shoot MEP rough-in. PMs search for "before drywall". PEs build the turnover package.

  2. 2 · IT NOTICESIt sees the pattern

    The same OAC photo pack every Friday. The same open-wall search on every unit.

  3. 3 · IT SHIPSA new screen, made for you

    It adds a field, a tool or a screen, and turns it on.

    Here is something we built for you.
  4. 4 · IT CHECKSKept or rolled back

    Each version is scored on use. A worse version rolls back by itself.

Every role on the job

Each person gets the screen the harness chose for them.

The harness writes one layout per role and changes it when the role's work changes. These are the layouts in the current version.

SuperintendentUnits closingNeeds youThis weekAsk your photos
Project managerNeeds youTime saversProgressAsk your photos
OwnerProgressAll projectsTime savers
Project engineerNeeds youCloseoutAsk your photosThis week
Safety managerHazardsNeeds youThis week
Self-improving harness · Recursive Harnessing

Every new feature came from how people used it.

Ten versions over seven years of a simulated general contractor. Each card says what the harness noticed on the jobs, then what it shipped. One change made answers worse, so it rolled back.

Simulated firm history (built-in copy)
Oldest first
Under the hood

Plan, Build, Instrument. Then the improver.

The stages run on a frozen copy of the policy: rules, context policy and tool grants. Only the improver writes a new policy, and only from what Instrument found. So each version has a reason you can read.

01 · PLANPick the sprint

Reads the last checkpoint and its measurements. Picks one sprint mode: feature, improvement or fix.

02 · BUILDRun the agent

Runs the coding agent (Claude Code today) with freezePolicy() and a store that refuses rule writes.

03 · INSTRUMENTMeasure it

Runs checks for ten capabilities in trade terms: MEP rough-in, OAC photo pack, closeout walk, turnover package, fall protection. Writes findings.

+ · IMPROVERewrite the harness

Turns findings into policy vn+1, tags git cp/n, and writes policies and checkpoints to Atlas.

Real terminal output · dry run

Every version is a checkpoint. Any checkpoint comes back.

  • Rules are data. Rules, context policy and tool grants live in a versioned policy, not in a prompt.
  • Checkpoints are durable. Git sha, policy version, scores and a retrospective, in MongoDB Atlas.
  • Rollback is one command. The old policy returns as a new version, so history is never lost.
TypeScript monorepo · Turborepo + pnpmHarness API · Cloudflare WorkerApp · Vite on Cloudflare PagesMongoDB Atlas · Sandbox clusterPhoto fields: unit, level, trade, wall, issue
MongoDB Atlas

Long-term memory is the database, not the context window.

Every stateful thing lives in one Atlas cluster. The stages read from it, the improver writes to it, and any version can be run again over the same data.

The harness

What it is, and how it got here.

policiescheckpointsharness_versionsplansfindingsmeasurements

The media

Photos are read once, then tiered.

media_indextranscriptsjobs

The contractor

The simulated GC it learns on: projects, photos, activity, outcomes.

demo_projectsdemo_photosdemo_activitydemo_outcomes
The workload

Built on real construction photos.

Openly licensed site photos and 20 NYC building records from NYC Open Data. Photos are the workload the harness learns on, not the product. It learns which fields matter: unit, level, trade, open or closed wall, issue.

Piling rig and cranes on an excavation site
Site
Aerial view of a steel frame structure
Steel
Scaffolding on a building under construction
Exterior
Workers fitting pipes inside a metal stud wall
Plumbing
An electrician at work in a timber frame
Electrical
Spray foam insulation applied under a floor
Insulation
A large excavation site with cranes and new buildings
Excavation
3 + 1stages, plus the improver that is the only writer
1MongoDB Atlas cluster for policies and checkpoints
20real NYC building records from NYC Open Data
1 dayevery line written at the hackathon, Sept 26, 2026

What is real and what is simulated: the loop, the policies, the checkpoints and the rollback are code in the repo. The firm in the app, with its years of jobs, is a simulation with a fixed seed.

Try it

Jobsite software that gets better every week.