API AI Tools

21st Agents SDK is the fastest way to add an AI agent to your app. Define your agent in TypeScript, deploy in one command, and embed a production-ready chat UI with built-in streaming, session management, usage billing, and observability.

Step 3.5 Flash is StepFun's 196B sparse MoE model that activates only 11B parameters per token. It delivers frontier reasoning and strong agentic performance with high efficiency.

AssemblyAI builds advanced speech language models that power next-generation voice AI applications. Its industry-leading speech-to-text delivers highly accurate transcription along with speaker detection, summarization, PII redaction, and an LLM gateway.

Notte is a platform for building and deploying enterprise-grade browser agents with managed infrastructure via a single API. It combines deterministic scripts with AI reasoning for production reliability.

Aura provides semantic version control specifically designed for AI-generated code by tracking mathematical logic instead of text lines. It offers flawless traceability for AI agents while saving 95% on LLM tokens and operates 100% locally.

Didit replaces fragmented identity tools with one platform that orchestrates KYC, biometrics, liveness, and fraud detection together. It offers 500 free checks per month with pay-per-use pricing and works globally across devices.

Octrafic is an open-source CLI for API testing that lets you describe tests in plain English. It handles everything from generating requests to validating responses and exporting PDF reports.

WebSocket Mode for the Responses API maintains persistent connections for AI agents, sending only incremental inputs instead of full context. This reduces end-to-end latency by up to 40% on heavy tool-call workflows.

Plain Markdown is a one-click browser extension that converts any webpage into clean Markdown format. It's also available as an API and is ideal for AI prompts, LLM workflows, and note-taking applications.

HelixDB is an open-source OLTP graph-vector database built in Rust that is now generally available after more than a year of development. It handles workloads ranging from indie hackers building custom agent memory to Fortune 500 companies needing infinitely scalable and highly available database solutions.