Building an Alien Language from Scratch with LangChain

A developer built a system where 100 AI agents, each with unique personalities, evolved a shared symbolic vocabulary through trade negotiations using LangChain.js pipelines, with no pre-programmed symbol definitions or mock data. The project uses three different LangChain patterns to handle agent complexity, including a custom `LenientJsonParser` that extends LangChain's `JsonOutputParser` to handle real-world LLM quirks like markdown code fences and empty content fields. The system supports instant provider swapping between OpenAI, Featherless.ai, and LM Studio by changing a single `baseURL` configuration.

How 100 AI agents evolved a shared symbolic vocabulary through trade — with no pre-programmed definitions, no mock data, and no shortcuts. Most emergent communication demos cheat. They hardcode symbol meanings, or use mock LLM responses, or simulate the entire thing with random number generators. The result is a demo that looks impressive but teaches you nothing about how actual language models behave when they need to coordinate. I wanted to build something real: two civilizations of AI agents, each with 50 unique personalities, negotiating trades using abstract symbols — where every single message and decision flows through a real LLM via LangChain SDK pipelines . No mock data. No hardcoded symbol mappings. Just pure reinforcement: successful trades reinforce a symbol's meaning, failed trades weaken it. Over hundreds of rounds, a shared vocabulary emerges. LangChain.js v1.4 is the backbone of this project. I deliberately used three different LangChain patterns to show how the SDK can handle different levels of agent complexity: js const chain = ChatPromptTemplate .fromMessages "system", prompt , "human", "{input}" .pipe model .pipe parser ; Every symbol an agent sends is generated through this pipeline. The ChatPromptTemplate injects the agent's personality, observations, recent successes/failures, and conversation history. The model returns structured JSON {"message": "🟢⚡🔺"} , which the JsonOutputParser validates. The trickiest part was the {{ escaping — LangChain uses {} for template variables, but I needed literal {} in the JSON example. The double-brace escape {{"message": "..."}} resolves this cleanly. Same structure, different prompt — but this one returns a boolean decision. {"accept": true} or {"accept": false} . The agent evaluates whether the proposed resource exchange is beneficial based on its observations and personality. This is where LangChain really shines. Using createAgent from the LangGraph-based SDK, I built a full ReAct agent that can: DynamicTool DynamicTool The agent literally thinks, uses tools, and then decides — all within LangChain's agent loop. The moment you switch from mock to real LLMs, everything gets interesting. Models wrap JSON in markdown code fences. They include chain-of-thought reasoning. They run out of tokens mid-response. They return empty content and put their thoughts in vendor-specific fields like reasoning content . I built a LenientJsonParser that extends LangChain's JsonOutputParser to handle all of these cases: class LenientJsonParser extends JsonOutputParser { async parse text: string : Promise<object { try { return await super.parse text ; } catch { // Strip {% endraw %} json ... {% raw %} fences // Match balanced braces for nested objects // Fall back gracefully } } } This was essential. Without it, models like Gemma 4 a reasoning model would output all their thinking in reasoning content and leave content empty, causing the parser to fail on every message. All three provider types — OpenAI, Featherless.ai, and LM Studio — use the same ChatOpenAI class from @langchain/openai . This means: baseURL config changeThe model factory in orchestrator.ts creates the right ChatOpenAI instance based on the config: function createChatModel config: SimulationConfig { switch config.provider { case "openai": return new ChatOpenAI { model: "gpt-4o-mini", ... } ; case "featherless": return new ChatOpenAI { model: "...", configuration: { baseURL: "..." } } ; case "lmstudio": return new ChatOpenAI { model: "...", configuration: { baseURL: ".../v1" } } ; } } Every provider swap is instant — no restart, no rebuild. I went through two complete redesigns. The first was dark cyberpunk — glowing elements, neon accents, dramatic. It looked great in screenshots but was exhausting to work with. The second is a premium light product aesthetic inspired by Civilization VI, Notion, and Stripe: box-shadow: 0 1px 2px rgba 0,0,0,0.04 Dark/light mode uses CSS custom properties mapped through @theme , with localStorage persistence and prefers-color-scheme detection. No Tailwind dark: variants cluttering the component code. Real LLMs are messy — JsonOutputParser fails the moment a model wraps output in markdown. Build lenient parsers from day one. Reasoning models need special handling — Gemma 4, DeepSeek R1, and similar models put everything in reasoning content and leave content empty. You need higher maxTokens and explicit "do not reason" instructions in the system prompt. {{ escaping is essential — LangChain's ChatPromptTemplate uses {} for template variables. JSON examples need {{ and }} to produce literal braces in the output. createAgent is powerful but expensive — the ReAct loop makes multiple LLM calls per decision. For simple trade evaluation, Pattern 2 a single chain call is more efficient. Use Pattern 3 when you need tool-use and multi-step reasoning. Template variable collision is real — LangChain's {} syntax conflicts with JSON's {} . The switch to {{ escaping was a "wait, that's it?" moment after hours of debugging. CSS custom properties + Tailwind = clean themes — mapping all colors through @theme variables instead of using dark: variants keeps component code readable and theming centralized. git clone https://github.com/harishkotra/alien-translator.git cd alien-translator npm install npm run dev Open the settings, configure an LLM provider, and click Start. Watch the language emerge. Code and more: https://www.dailybuild.xyz/project/147-alient-translator https://www.dailybuild.xyz/project/147-alient-translator