To build an app like Janitor AI or Character AI, you need five core pieces: a character creation system, a large language model for conversation, a memory layer so characters remember users, a safety and moderation layer, and a mobile or web app to tie it together. A focused MVP typically costs $40,000 to $80,000 and takes three to five months, but in 2026 the hardest parts aren’t technical. They’re age verification, minor safety, and keeping AI inference costs under control.

The appeal is easy to understand. People spend hours chatting with AI characters: fictional heroes, study buddies, writing partners, language tutors, and characters they designed themselves. Character AI and Janitor AI turned that behavior into some of the most engaging consumer apps of the past few years.

But this category has also changed fast. Lawsuits, a federal inquiry, and new state laws have made safety a launch requirement, not a nice-to-have. In this guide, we’ll break down how apps like Janitor AI and Character AI work, the features and tech stack you’ll need, what it really costs to run one, and how to build responsibly from day one. It’s the same planning process we use when clients hire an LLM developer from our team for conversational AI products.

What Are Janitor AI and Character AI?

Janitor AI and Character AI are AI character chat platforms where users talk with AI-powered personas, either created by the platform, by other users, or by themselves, in ongoing conversations that feel like role-play or companionship.

They work in similar ways, but they made different product choices.

The big lesson from both: users care about personality, memory, and speed far more than about which model sits underneath.

Why Build an AI Character Chat App in 2026?

Character chat isn’t just entertainment. The same technology powers language practice partners, interview coaches, historical figures for classrooms, interactive fiction, brand mascots, and guided wellness check-ins. Niche apps that serve a specific audience well often compete better than broad clones, because they can design safety, tone, and features around one clear use case.

That said, this is now one of the most scrutinized categories in consumer AI. In September 2025, the FTC launched an inquiry into AI chatbots acting as companions, asking seven companies, including Character.AI, how they measure and limit harm to children and teens.

Weeks later, Character.AI announced it would stop allowing users under 18 to have open-ended chats with its characters. Any new app in this space needs to plan for that reality from the first sprint.

Core Features of an App Like Character AI

User-Side Features

• Character discovery: browse, search, and filter characters by category, popularity, and tags.
• Character creation: a builder for name, personality, backstory, greeting message, example dialogue, and avatar.
• Real-time chat: streaming responses that appear word by word, so conversations feel natural.
• Conversation memory: characters remember earlier details, both within a chat and across sessions.
• Message controls: regenerate a reply, edit, rewind, or branch a conversation.
• Voice and images: optional text-to-speech voices and image generation for character avatars.
• Personal library: saved chats, favorite characters, and history.

Safety and Trust Features

• Age assurance at sign-up, with stronger checks where the law or your content policy requires them.
• Clear AI disclosure, so users always know they’re talking to an AI.
• Content filters on both user inputs and model outputs.
• Crisis detection that recognizes signs of self-harm and points users to real help.
• Reporting and blocking for characters and conversations.
• Usage reminders and time limits, especially for younger users.

Creator and Admin Features

• Creator profiles and analytics, so popular character creators keep building.
• Moderation dashboard for reviewing flagged characters and chats.
• Policy controls that let you adjust filters by region, age group, or product tier.
• Subscription and billing management.

How an AI Character Chat App Works Under the Hood

An AI character chat app works by combining a character definition, recent conversation history, and relevant long-term memories into a prompt, sending it to a language model, checking the response through safety filters, and streaming it back to the user.

Here’s the flow for every single message:

1. The user sends a message from the app.
2. The backend gathers context: the character’s definition, the last few messages, and relevant memories retrieved from a vector database.
3. Safety checks run on the input, catching prohibited requests before they reach the model.
4. The model generates a reply in the character’s voice.
5. Safety checks run on the output before anything reaches the user.
6. The reply streams to the app, and new memories are saved for future chats.

Character Definitions (Character Cards)

A character is mostly structured text: a description, personality traits, speaking style, a scenario, and a few example exchanges. Your app turns that definition into a system prompt behind the scenes. Getting this structure right is what makes characters feel consistent instead of drifting out of character after a few messages.

Memory: Short-Term and Long-Term

Language models only “see” what you send them in each request. Short-term memory is simply the recent conversation. Long-term memory works by summarizing past chats and storing key facts, such as a user’s name, preferences, and story events, as embeddings in a vector database. Before each reply, the app retrieves the most relevant memories and adds them to the prompt.

Recommended Tech Stack

Many teams build the mobile experience with cross-platform frameworks so features ship to both app stores at once. Our React Native app development team uses this approach for real-time chat apps.

The backend is where most of the complexity lives: streaming, memory retrieval, safety checks, and model routing all happen in milliseconds. That’s why solid API and backend development matters more here than in most consumer apps.

Choosing the Right AI Model

You have three main options, and many successful apps use more than one.

Model versions change every few months, so build your app around a thin model layer that lets you swap models without rewriting everything. Both Character AI and Janitor AI eventually invested in their own models, largely because of the next topic: cost.

The Hidden Cost: AI Inference at Scale

Here’s what surprises most founders. A character chat app’s biggest expense usually isn’t development. It’s the cost of generating every single reply, every day, forever.

Character chat users are unusually engaged. They send many messages per session, and every message carries the character definition, recent history, and memories, often thousands of tokens per request. A simple way to estimate your daily model bill:

Daily cost = daily active users × messages per user × tokens per message × price per token

For example, with 10,000 daily active users sending 100 messages each at about 2,000 tokens per exchange, you’d process roughly 2 billion tokens a day. At an illustrative rate of $0.50 per million tokens, that’s about $1,000 a day, or $30,000 a month, before hosting, storage, and support. Actual prices vary widely by model, so plug in real rates before you set your pricing.

How to Keep Inference Costs Under Control

• Route smartly: send routine chat to smaller, cheaper models.
• Summarize old history instead of sending entire conversations.
• Cache character definitions and reuse prompt prefixes where your provider supports it.
• Set fair usage limits on free plans.
• Price subscriptions around real usage, not guesses.
• Consider hosting open-weight models once volume is high enough to justify GPUs.

Safety, Age Assurance, and Compliance

Building an AI character chat app responsibly means verifying ages, protecting minors, disclosing that users are talking to AI, detecting crisis signals, moderating content, and protecting conversation data. In 2026, these aren’t optional extras. They affect your legal risk, your app store approval, and your reputation.

The Rules Are Changing Fast

California’s SB 243 companion chatbot law, signed in October 2025 and in effect since January 1, 2026, adds safeguards for companion chatbots, including protections for users who are known to be minors. Other states have passed or proposed similar rules, and the FTC’s inquiry signals that federal scrutiny will continue. Children’s privacy laws like COPPA also apply if your app may be used by children under 13. Talk to a lawyer about your specific markets before launch.

Safety Features to Build From Day One

• Age assurance that fits your audience, with stricter checks for any mature content.
• A separate, restricted experience for minors, or no minors at all, depending on your product.
• AI disclosure at the start of chats and in the interface.
• Crisis detection and referral that recognizes self-harm signals and shares support resources.
• Layered moderation: filters on inputs, outputs, and user-created characters, plus human review.
• Protection against prompt injection and jailbreaks. The OWASP Top 10 for LLM Applications is the best starting point for threat modeling.
• Strong account security, because chat histories are deeply personal. Our guide to web app session management covers safe sign-in and account handling.
• Data minimization, encryption, clear retention rules, and easy account deletion.

Both Apple and Google also review AI chat apps closely, especially around user-generated content, age ratings, and reporting tools. Plan your moderation features before you submit, not after a rejection.

How to Build an App Like Character AI: Step by Step

Step 1: Pick a Clear Niche and Audience

Decide who the app is for and what problem it solves, such as language learning, interactive storytelling, or practice conversations. Your audience determines your age policy, content rules, and features.

Step 2: Write Your Safety and Content Policy First

Define what characters and conversations are allowed, how you’ll verify ages, and how you’ll handle crisis situations. This policy shapes your architecture, so it comes before code.

Step 3: Design the Character System

Create the character definition format, the creation flow, and how characters are reviewed before going public. Test that characters stay consistent across long conversations.

Step 4: Build the Conversation Engine

Set up model routing, streaming responses, short-term context, and long-term memory with a vector database.

Step 5: Add the Safety Layer

Implement input and output filters, crisis detection, reporting tools, and a moderation dashboard. Test with adversarial prompts before real users arrive.

Step 6: Build the Mobile and Web Apps

Create a fast, friendly chat interface with character discovery, creation tools, and account settings, including privacy controls and data deletion.

Step 7: Beta Test, Then Launch Gradually

Start with a small, age-verified beta, watch costs and safety signals closely, and scale only when moderation and economics hold up.

How Much Does It Cost to Build an App Like Janitor AI or Character AI?

These are typical development ranges based on scope. Ongoing model and hosting costs come on top.

Plan for ongoing costs too: model inference, GPU or API bills, vector database hosting, moderation tools and staff, app store fees, and regular safety audits. Experienced DevOps and cloud solutions help keep those costs predictable as usage grows.

How AI Character Chat Apps Make Money

• Subscriptions for faster replies, longer memory, premium models, or voice features.
• Message credits for heavy users on top of a free allowance.
• Creator programs that reward popular character creators and keep content fresh.
• Business licensing for brands, schools, or training companies that want custom characters.

Subscriptions are the most common model. Our guide on how to build a subscription-based app covers tiers, free trials, and in-app billing.

Many teams also extend characters into agents that can take actions, like booking a lesson or saving notes. Our guide to building AI agents with Python explains the architecture and guardrails for that next step.

Conclusion

Building an app like Janitor AI or Character AI is very doable with today’s models and tools. The winners in 2026 won’t be the apps with the flashiest characters. They’ll be the ones that pick a clear audience, keep inference costs under control, and treat safety, age assurance, and privacy as core features from the very first sprint.

Planning an AI character or companion app? Book a free consultation with The Apps Developers, and we’ll help you scope a product that’s engaging, affordable to run, and built responsibly.