How to Build a Chatbot with an LLM API

A chatbot commonly receives a user turn, sends it to a model service, and displays the returned answer. The application wraps that exchange with conversation identity, history, instructions, and error handling. There is no universal LLM API schema: some endpoints use role-tagged message arrays, while others define different input and output objects. In OpenAI’s Chat Completions pattern, the client sends messages and usually carries prior turns forward itself. OpenAI recommends the Responses API for new projects; Chat Completions remains supported. Responses offers explicit options for chaining responses or using Conversations, so a developer should not assume every endpoint is stateless or every provider stores a session. Streaming can show partial output while generation continues, but the UI must handle completion, interruption, and errors. Tool calling adds another loop: the model requests a function, application code validates and executes it, then sends the result back for a final answer. Treat these requests as untrusted suggestions, enforce authorization and input validation, and keep side effects under application control. Production chatbots also need rate-limit handling, bounded retries, timeouts, token and cost management, user-facing fallbacks, and safety checks appropriate to the task. Keep API credentials on a server, never in client-side code. Decide what conversation data to store and for how long, and consult each provider’s current data controls. Do not send secrets or unnecessary personal data in prompts. Test long conversations and provider-specific failures before deployment.