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KW

000 m/Full-stack web developer · freelance

Keyson William

I build websites, platforms and custom systems, from interface to persistence, with security designed in layers.

030 m/route

What I do

From the website that presents your business to the system that runs your operation. Each service points to a real project where you can see it in practice.

How I work

Each project in this portfolio shows part of the same process. These are the steps, with the cases where each one appears.

  1. Step 1

    Understand the process

    Before the first line of code, I map how the work happens today: pages, data, steps and what cannot be lost.

  2. Step 2

    Plan the structure

    I define the layers, the data and who can access what, leaving room for the project to change direction without starting over.

  3. Step 3

    Build it securely

    Delivery in stages, with protection at every layer and automated tests where the risk is highest.

  4. Step 4

    Launch and follow up

    Cutover without downtime, tracking what matters and adjustments based on real use.

060 m/service

Featured projects

Three projects available online, each with a case study on decisions, architecture and results.

sample 01/in production

Visa Contabilidade

Migration of a WordPress corporate site to Next.js, focused on local SEO, specialist content and protected forms.

  • MDX blog and accounting glossary
  • Structured data and sitemap
  • Form with Zod, Turnstile and rate limiting

sample 02/functional MVP

Simone Educação Digital

Course platform with a public site, student area and admin panel in a single monorepo.

  • Stripe payments with signed webhook
  • Videos and files served only to entitled users
  • Security test suite

sample 05/in production

SK Agency

Corporate and operational platform for an agency: website, client portal and admin management.

  • Portal with campaigns, reports and contracts
  • Stripe, Google Ads and Resend integrations
  • Private files via expiring URLs
Case studyVisit site

Code not public

090 m/repository

Security in layers

Protection designed in layers, from the interface to the database: if one fails, the next still holds. Below, an attempt to open another user's data being blocked.

  1. 000 m/interface

    • Output escaping (React)
    • CSP
    • HSTS
    • X-Frame-Options
    • Referrer-Policy
  2. 030 m/route

    • Rate limiting
    • Anti-bot (Turnstile)
    • Origin check
    • Signed session (HMAC)
    • Session revocation
  3. 060 m/service

    • Zod validation
    • RBAC
    • Ownership check (anti-IDOR)
    • Webhook signature
    • MIME allowlist
    • Non-enumerable codes
  4. 090 m/repository

    • Parameterized queries
    • Tenant scoping
    • Atomic operations
  5. 120 m/persistence

    • RLS
    • bcrypt
    • AES-256-GCM

120 m/persistence

Let's talk

Available for freelance projects: websites, landing pages, platforms and custom systems. Tell me about your idea on WhatsApp, email or LinkedIn.