CertusQS
CertusQS is a SaaS platform for the UK contractor's monthly commercial cycle, built around the contract Bill of Quantities as a single data spine. Contractor QS teams spend four to five days each month reconciling valuations, variations and payment applications across disconnected spreadsheets, risking missed Construction Act deadlines and unauditable figures.
Client
CertusQS
Category
Commercial SaaS · UK Contractor Valuations
Platforms shipped
3 platforms
Status
V1 test build · 2026
The Challenge
CertusQS is a SaaS platform for the UK contractor's monthly commercial cycle, built around the contract Bill of Quantities as a single data spine. Contractor QS teams spend four to five days each month reconciling valuations, variations and payment applications across disconnected spreadsheets, risking missed Construction Act deadlines and unauditable figures. The project required a deep understanding of the domain and a meticulous approach to user experience design. We needed to build something that was not only visually stunning but also incredibly fast and reliable at scale.
Our Solution
CertusQS locks the BoQ at contract execution and routes every change through auditable variations, computes all money server-side in int64 pence, and schedules statutory payment notices from the contract terms rather than manual dates. An AI-assisted BoQ import reads a contract bill of quantities straight from the supplied document into structured, priced line items — so a new project starts without hand-keying hundreds of rows. A guided valuation build-up, a variation register and generated Applications for Payment share one evidence-backed audit trail, on a Next.js frontend over a Go/Gin API. Currently a V1 test build.
Key Results
int64 pence
Money precision
Auto from contract
Statutory deadlines
Go + Next.js
Architecture
V1 test build
Status
AI Integration
CertusQS uses AI to make importing messy, real-world Bill of Quantities spreadsheets reliable — without ever letting the model produce a number. The AI only interprets how each spreadsheet should be read; a deterministic parser then does the arithmetic, taking every figure straight from the original cell, so the contract sum stays traceable to the source file.
Built with
Vercel AI Gateway · Anthropic Claude (Sonnet) · Go backend (no SDK)
Exactly how AI is used
- Analyse — the model reads a bounded sample of the uploaded spreadsheet and proposes how to read it: which row is the header, which columns are quantity/rate/total, and which rows are sections, subtotals or additions.
- Review — after parsing, it reads back the produced bill and raises advisory findings (e.g. a restated tender sum that would double-count the total); findings never block the import.
- Chat — a surveyor can correct the reading in plain language (“column F is the rate, not the total”) and get a revised result or line edits.
- The model returns a structured JSON “plan” that is validated against the actual sheet before it is applied; any figure not taken from a cell is marked “hand-made” in the bill and the audit trail.
- Model-agnostic via the Vercel AI Gateway (Anthropic Claude by default); the deterministic import keeps working even with AI switched off, and it can be disabled per organisation or per job.
- Every AI call is cost-metered and attributable per client and project. (No RAG, embeddings or tool-calling — the sheet sample travels with each request.)
Tech Stack
What we delivered
3 platforms shipped end-to-end.
- QS web application (dashboard, valuations, variations, AfPs, reports)
- Grit-generated support/ops admin console
- Go/Gin REST API with RBAC & background jobs
Platforms
Integrations
- AIAI-assisted BoQ import
Authentication
Infrastructure & more
- AI-assisted BoQ import — document to structured bill
- Background jobs & cron (asynq/Redis)
- Server-side PDF generation
- S3-compatible storage (MinIO)
- Immutable audit trail
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