🧰 AI Engineering Stack

The field-tested toolbox behind R21 Digital & my open-source work

The models, agent/MCP infrastructure, retrieval, voice, and app stack I actually build and ship production systems with.

_{Not a link dump — every tool here I've shipped with, run in production, or evaluated hands-on for a real project. ★ = day-to-day core.}

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Core stack, at a glance

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🤖 LLM Providers & Model APIs

	Tool	What I use it for
★	Anthropic / Claude	Primary model family for agentic + tool-calling work.
★	OpenRouter	Single gateway for multi-model routing (cost/latency per task).
★	Groq	Low-latency inference for fast agent steps.
	OpenAI	GPT models via the API.
	Google AI Studio / Gemini · Vertex AI	Gemini models, prompt tooling, GCP-hosted inference.
	Mistral AI	Open-weight models.
	Moonshot / Kimi	Long-context model API.
	xAI / Grok	Grok model console.
	Hugging Face	Model hub, hosted inference, Spaces.
	NVIDIA NIM	GPU-served model endpoints.

🔌 Agents, MCP & Orchestration

	Tool	What I use it for
★	Model Context Protocol	The standard I write servers/tools against — my published server.
★	Make.com	Production automation orchestration for client work.
★	n8n + n8n-mcp	Self-hostable workflow automation + AI nodes.
	Relevance AI	Agent + tool marketplace platform.
	Rasa	Open-source conversational NLU / dialogue framework.
	Huginn	Self-hosted "agents that watch and act."
	Context7 · Playwright MCP	Live library docs and browser control, as MCP tools.
	ClickUp · Metricool · NotebookLM	Business systems wired to agents over MCP rather than scraped.

🧠 RAG, Retrieval, Search & Scraping

	Tool	What I use it for
★	Pinecone	Vector DB for RAG + agent memory.
★	Exa	Neural search API for agents.
★	Tavily	Search/extract API purpose-built for LLMs.
★	Firecrawl	Turn sites into LLM-ready markdown.
	LangSmith / LangChain	Tracing + eval for LLM apps.
	Brave Search API	Privacy-first web search.
	SerpApi	Structured search-engine results.
	Apify	Full-stack scraping + data extraction.
	SearXNG	Self-hosted metasearch.

🎙️ Voice, Speech & Transcription

	Tool	What I use it for
★	ElevenLabs	TTS / voice generation.
★	Deepgram	Real-time speech-to-text.
★	faster-whisper	Local, private transcription — my default (no paid API).
	AssemblyAI	Transcription + audio intelligence.
	Speechmatics	Multilingual STT.
	Vapi · Retell AI	Voice-agent frameworks.

🖥️ Backend, Data & Infra

	Tool	What I use it for
★	Supabase	Postgres + auth + storage for most products.
★	PostgreSQL	Primary relational store.
★	Vercel	Deploy target for Next.js apps.
★	AWS	SES email, EC2/PM2 hosting, HIPAA-eligible infra.
	Redis	Cache / queues / rate-limiting.
	Railway · DigitalOcean	Container / VPS hosting.
	Clerk	Auth + user management.
	Firebase	Realtime / auth where it fits.

✉️ Email & Messaging Infra

Tool	What I use it for
★ AWS SES	Transactional email standard across R21.
Postmark · SendGrid	Transactional email.
WAHA	Self-hosted WhatsApp HTTP API.
AgentMail	Inboxes for agents.

🎨 Frontend, App Builders & Design

	Tool	What I use it for
★	Next.js · React · Tailwind	Core web stack.
★	v0 by Vercel	AI UI generation.
	Figma	Design + handoff.
	21st.dev	Component library / inspiration.
	Retool · Appsmith	Internal tools & admin panels.
	WeWeb · Firebase Studio · Emergent	No/low-code builders (evaluated).

📱 Mobile & Cross-Platform

	Tool	What I use it for
★	Flutter / Dart	One codebase to six targets. Shipped a tournament + catch-logging app that has been in the field since 2025.
★	PWA	For when a store listing is the wrong answer. I write the service worker by hand because the caching rules are specific to the app and a plugin buries them.
	App Store Connect · Play Console	Store submission, review policy, account-deletion requirements.

💻 AI Coding Environments

	Tool	What I use it for
★	Claude Code	Primary agentic dev environment.
★	OpenAI Codex	Second-model adversarial review before anything public ships. It catches what Claude and I both missed.
	t3code	Multi-agent orchestration over one repo. I contribute upstream to it.
	Cursor	Editor-native agent work.
	Warp	Agentic terminal.
	Windsurf · Kiro · Factory · Qoder · Cosine · Kilo Code	Evaluated AI IDEs / agents.
	Replit · Bolt.new · Blink	Prototyping sandboxes.

🎬 Media Generation

Tool	What I use it for
Runway · Remotion · Shotstack	Video generation / programmatic video.
Midjourney · Stability AI · DALL·E	Image generation.
Kie.ai	Aggregated media-generation APIs.

🧩 Self-Hostable Building Blocks

Tool	What it is
Sentry	Error tracking + performance.
Metabase	BI / dashboards.
Cal.com	Scheduling infrastructure.
Chatwoot	Omni-channel support desk.
Mautic · EspoCRM · OpenProject	Open-source marketing / CRM / PM.

📊 Data, Payments & Discovery APIs

Tool	What I use it for
★ PostHog	Product analytics — funnels on the paths that actually matter, self-hostable if the data is sensitive.
Stripe	Payments & billing.
RevenueCat	In-app subscriptions.
Mapbox	Maps / geodata.
Twelve Data	Market data API.
Apollo	B2B data + enrichment.
PageSpeed Insights · Search Console	Performance + GEO/SEO.

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_{Maintained by Carlos Jimenez — Forward-Deployed / Applied AI Engineer.
Curated from a working practitioner's toolbox; opinions are field notes, not endorsements.}