The building blocks for headless and agentic software

Discover and compare the APIs behind chat, UI, voice, video, data, automation, and agents.

API Building Blocks

Discover the APIs behind chat, UI, voice, video, data, automation, and agents. Compare capabilities and choose the right building blocks for headless and agentic software.

11 listings · Last updated Sep 14, 2026

Category
Pricing model
Authentication
Free tier(8)Open source(1)

Showing 11 of 11 listings

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Context.dev
Context.devFeatured

A web data API for scraping and crawling sites, extracting structured content, retrieving brand and company data, and enriching entities for AI agents and products.

Data & Knowledge
Freemium
Bearer token
✓Yes—No
Algolia Search API

A hosted search and discovery API for indexing records, running keyword and AI-assisted search, configuring ranking, filtering results, and adding recommendations and personalization.

UI & Experiences
Freemium
API key
✓Yes—No
Clerk Backend API

An identity and user management API for users, sessions, organizations, invitations, tokens, machine authentication, API keys, and application authentication workflows.

Identity & Security
Freemium
Bearer token
✓Yes—No
ElevenLabs API

A voice and audio API for text to speech, speech to text, conversational voice agents, dubbing, sound effects, voice transformation, and audio processing.

Voice & Audio
Freemium
API key
✓Yes—No
HeyGen API

A video generation API for creating avatar videos, translating and dubbing video, generating speech, producing videos from templates, and working with avatar, voice, and template libraries.

Video & Avatars
Usage-based
API key
—No—No
Inngest API

A durable execution and workflow API for event-driven functions, background jobs, queues, retries, concurrency, throttling, scheduling, and workflow observability.

Automation & Orchestration
Freemium
API key
✓Yes✓Yes
OpenAI API

A model API for building text, reasoning, multimodal, realtime, image, audio, and agentic applications through hosted models and tools.

Models & Agents
Usage-based
API key
—No—No
Pinecone API

A managed vector database and inference API for storing and searching records, generating embeddings, reranking results, and building retrieval and knowledge applications.

Data & Knowledge
Freemium
API key
✓Yes—No
Resend API

An email API for sending and receiving transactional email, managing domains, contacts, broadcasts, templates, webhooks, and delivery events.

Chat & Messaging
Freemium
API key
✓Yes—No
Stripe API

A payments and financial infrastructure API for accepting payments, managing subscriptions, sending payouts, running platforms and marketplaces, and automating revenue workflows.

Payments & Commerce
Usage-based
API key
—No—No
Vercel REST API

A platform API for managing deployments, projects, domains, environment variables, logs, caches, integrations, teams, and other application infrastructure.

Infrastructure & Observability
Freemium
Bearer token
✓Yes—No