Spec-Driven Development | the spec leads every step

Software on the schedule and budget we committed to.

You describe what you need in your own words. We turn it into a spec you read and approve, and a time and budget estimate we stand behind. All the way to a working system in production.

A binding estimate comes after a spec phase, not after one call. Anyone who gives you a number after an hour is guessing.

Call You talk. We record. Spec Two versions. Rule book. Approval + estimate You approve. We commit. Build and test AI agents, supervised. Review Staging. Fixes. Production Hosting. Upkeep. Live docs.
Blue: AI does the workGreen: a person decides

We commit to time and budget

A spec you approve, an estimate we meet, and a system that goes live. One team for the spec, the build and the upkeep.

  • A binding estimate after the spec, not after a call
  • Every change goes through the spec before any code

The development rule book

Hundreds of rules gathered over decades, in chapters such as security, performance and user experience. Every requirement we write is checked against them.

  • The spec covers what you did not know to ask for
  • Two versions: one for you, one for developers

Software houses since 1989

Owners who have run software houses since 1989, development in India since 2004, a presence in Portugal since 2023. Our own products have run at customer sites for years.

  • ISO 27001 certified, working to the OWASP Top 10
  • Experienced developers are accountable for every line

Among our clients

  • Drive Group
  • IKEA
  • Israel Police Funds
  • Rafa Laboratories
  • Daniel Group
  • Margoa Residences
  • Mor Institute
  • Israel Sports Betting Board
  • Student-Room-Flat
  • Hold-Me
Our services

One foundation. Four services.

Each one gives you a spec you approve, an estimate we meet, and code that stays documented.

For organizations

Software for organizations

A new system, a legacy replacement, or AI inside a product you already run.

Software is not your business, but the system is. We build it documented, readable and maintained, so you never depend on one person or one vendor. Security by default: ISO 27001, OWASP Top 10, hardened servers.

  • New systems
  • Legacy replacement
  • AI integration
For founders

From prototype to production

From an idea, or a prototype that got stuck, to a product you can raise money on.

We tell you what to build now, what to postpone and what it will cost, before you spend a cent. Built it in Lovable or Bolt and hit a wall? We take it to production, with security and code any team can pick up.

  • Proof of Concept
  • MVP
  • Prototype to Production
For companies with an in-house dev team

Dev team modernization

Consulting and hands-on rollout of AI-assisted development in the team you already have.

Bought the licenses and watched developers drift back to the old way? We install what runs our own development, the toolkit, the Skills and the development rule book, on your repo, and work alongside the team until it becomes how they work. Early partner program, limited places.

  • Agentic Engineering
  • Spec-Driven Development
  • Team coaching
For business owners

Business automation

Connections between your systems, built like software.

Automation that does not fail silently: a spec, error handling, monitoring, and full ownership of the accounts and workflows. n8n, Make or Zapier, whichever fits, and code where the tool runs out.

  • System integration
  • Monitoring and alerts
  • Full ownership
How it works

Three steps. At each one you know exactly what you get.

1
Free

Call

One hour. You talk, we ask and record. At the end you get what we understood, the questions that will set the scope, and a fixed price for the spec phase.

2
Fixed price

Spec

The meeting recordings become a spec in two versions: one you read and approve, and one for developers that includes what you did not know to ask for. At the end: a binding time and budget estimate.

The spec is yours, even if you decide not to continue with us.

3
On the budget and schedule you approved

Build and delivery

AI agents write and test the code. Experienced developers supervise and are accountable for every line. The spec and the code stay current and documented through delivery, and after it.

In DocsRobot, our own product, an AI system tests the product every night, in Hebrew and English, and files its own bug reports.

Why is the spec paid? Because that is the part where we work for you rather than sell to you. Our commitment applies to the spec you approved. Want to change something midway? The change goes through the same spec, and you see its effect on time and budget before you approve it, not after.
The development rule book

Your spec covers what you did not know to ask for.

Every requirement we write is checked against our development rule book: hundreds of rules gathered over decades, in chapters such as security, performance and user experience. A rule that applies and is not obvious goes into the developer version of the spec. No client asked for these up front. All of them are in every system we build.

How do you test something that happens once a month without waiting a month?

What you get: monthly billing, a weekly report, a yearly reminder. All fully tested before launch, not after the first month has passed.

The rule: any system with daily, weekly, monthly or yearly processes runs on a simulation clock we control, not on the server clock. In testing we move the clock forward and watch what happens. Without it there is no full acceptance test for a recurring process, only waiting and hoping.

A double click never charges twice.

What you get: no customers charged twice, no duplicate records, no “how did this happen?” calls to support.

The rule: every operation with side effects (creating a record, charging, sending an email, requesting a signature) takes an Idempotency-Key. The server claims the key atomically, stores the request hash with the final response, and returns that same response on every repeat. Same key with a different body: 409. Networks and clients retry; that is not a fault, it is reality. With this rule, a retry turns from a source of bugs into a safety mechanism.

One customer’s data cannot reach another customer. By design.

What you get: isolation at the architecture level, with an automated test that runs on every build. A mechanism, not a promise.

The rule: in a multi-tenant system the tenant identity comes only from the authenticated token, never from an ID sent in the body, a header or the URL. Filtering is enforced in one central place, so a missing filter is structurally impossible. Automated tests with two tenants confirm that A cannot see B through any endpoint. We do not rely on discipline; we build it so the mistake cannot happen.

More sample rules, and how they enter the spec

A commitment we kept

Two months, the budget we quoted, and a system that went live.

When the SaaS vendor we depended on threatened to shut down our system, we had about two months to replace it with one of our own. Assembly listened to what we needed, came back with a clear scope, a delivery date and a budget, and delivered exactly that, on the date and budget they quoted.

That version went live and became the foundation of our digital business. Since then Assembly has effectively been our in-house technology team, with no surprises in our financial planning. If you need a partner who will tell you what is possible, when and for how much, and then do it, I recommend Assembly without hesitation.

Cyril, Managing Partner, Student-Room-Flat
In our own product too. In DocsRobot, the document generator and e-signature system we build and sell, every new module was developed within the budget set for it in advance.
And the ventures that did not make it? We have seen many of them up close. Most did not fail because of the code; the money ran out before the product was ready. That is why every founder project with us starts by deciding what not to build yet.
Clients on working with us

People who worked with us, on what mattered to them.

What sets Assembly apart is that you get local guidance and service, at the quality you expect from an Israeli supplier, while the cost is significantly lower than similar service in Israel. The flexibility to start and pause development helps put the effort where and when it is needed.

Ofer, CEO, Wizenet

Although I worked directly with developers in India for many years, I chose to move our development to Assembly. The service is a different experience altogether: someone who really understands you and does not dodge direct questions, and a company that feels responsible for what it delivers. If you know what you want and need a professional force multiplier, talk to Assembly.

Mani, CEO and Owner, Hold-Me
Questions we hear

Before you call

Why is the spec phase paid, rather than part of the quote?
Because a good spec is work: recorded meetings, analysis, writing in two versions and checking against the rule book. The last system we specified took about thirty hours of meetings. A vendor who gives you a binding number after one call is guessing, and you pay for that guess later. The spec stays yours either way.
What happens when we change a requirement mid-build?
The change goes through the spec. You see what it does to time and budget, and approve it or not, before anyone writes code. Our commitment applies to the spec you approved, which keeps it real even after ten changes.
Is the spec mine if I do not continue with you to development?
Yes. Both the spec and the estimate. You can take them to any other vendor.
Where are the developers, and who is accountable?
Experienced developers in India supervise the AI agents and are accountable for every deliverable. You work with our management in Israel, and responsibility for the project is ours, not someone’s “over there”.
What does the AI actually do, and what does it not do?
It turns call recordings into a spec, prepares technical instructions, writes code and tests, runs the tests and files bug reports. It does not decide what to build, does not approve architecture and does not deliver to the client. At each of those points there is a person, and you can see who.
What about security?
We are ISO 27001 certified. We work to the OWASP Top 10, harden client servers to the relevant standards, and run automated penetration tests on large projects. Part of the rule book deals with security, so it is in the spec rather than added at the end.
The first step

One hour. No commitment.

At the end you will know what we understood, which questions are open, and what the spec will cost. If we think it is not worth building, we will say that too.

We reply within one business day. One hour, free, no commitment. Your details are used only to reply to you, as described in our privacy policy.

Or directly: info [at] assemblyso.com