Documentation

Host An App is a zero-config API for hosting HTML apps, Markdown documents, and Mermaid diagrams. Deploy content, get a public URL instantly. Works via REST API or MCP for AI agents.

Instant Deploy

One API call. Live URL in under a second.

AI-Native

MCP protocol for direct agent integration.

Ephemeral

Auto-expires after 7 days. No cleanup needed.

Quick Start

Deploy your first app in one curl command:

bash

curl -X POST https://hostan.app/api/v1/deploy \
  -H "Content-Type: application/json" \
  -d '{
    "name": "my-first-app",
    "content": "<!DOCTYPE html><html><body>Hello World</body></html>"
  }'

Response:

201 Created

{
  "id": "dep_01k8x7n1f8k0",
  "slug": "my-first-app",
  "url": "https://hostan.app/my-first-app",
  "created_at": "2026-06-10T20:00:00Z",
  "expires_at": "2026-06-17T20:00:00Z"
}

Deploy Markdown or Mermaid content by setting the type field:

bash

curl -X POST https://hostan.app/api/v1/deploy \
  -H "Content-Type: application/json" \
  -d '{
    "name": "hello-md",
    "content": "# Hello\n\nThis is **Markdown**.",
    "type": "markdown",
    "title": "Hello MD"
  }'

Or deploy a Mermaid diagram:

bash

curl -X POST https://hostan.app/api/v1/deploy \
  -H "Content-Type: application/json" \
  -d '{
    "name": "my-diagram",
    "content": "graph TD\n  A[Start] --> B[End]",
    "type": "mermaid",
    "title": "My Diagram"
  }'

💡

That's it!

Your app is now live at the returned URL. It will automatically be removed after 7 days. No account, no signup, no configuration needed.

Deploy Application

POST

/api/v1/deploy

Creates a new deployment. The content field accepts HTML, Markdown, or Mermaid diagram source depending on the type field. If name is omitted, a random slug is generated.

Request Body

application/json

{
  "name": "weather-dashboard",    // optional, 3–63 chars
  "content": "<!DOCTYPE html>..."  // required, max 1 MB
  "type": "markdown",           // optional, "html", "markdown", or "mermaid"
  "title": "My Page",            // optional, page title (markdown / mermaid)
  "one_time": true                 // optional, self-destructs after first visit
}

Parameters

Field	Status	Type	Description
`name`	optional	string	Preferred slug. Lowercase letters, digits, and hyphens. 3–63 characters. Auto-generated if omitted or taken.
`content`	required	string	HTML, Markdown, or Mermaid diagram source. Must be valid UTF-8 and under 1 MB.
`type`	optional	string	Interpretation of `content`. Default `"html"` — served as-is. `"markdown"` — rendered to HTML with a clean dark-themed layout. `"mermaid"` — rendered as an interactive diagram page with source tab.
`title`	optional	string	Page `<title>` and H1 heading. Applies when `type` is `"markdown"` or `"mermaid"`.
`one_time`	optional	boolean	If `true`, the deployment self-destructs after the first visit.

Success Response

201 Created

{
  "id":         "dep_01k8x7n1f8k0",
  "slug":       "weather-dashboard",
  "url":        "https://hostan.app/weather-dashboard",
  "created_at": "2026-06-10T20:00:00Z",
  "expires_at": "2026-06-17T20:00:00Z"
}

Health Check

GET

/healthz

Returns the service health status. No authentication required.

200 OK

{ "status": "ok" }

Error Responses

400 Bad Request

Missing html field, invalid slug format, or empty payload.

413 Payload Too Large

Request body exceeds the 1 MB limit.

429 Too Many Requests

Rate limit exceeded (10 deploys/min/IP). Retry after the indicated cooldown.

500 Internal Server Error

Unexpected server failure. Retry once, then contact support.

MCP Overview

Host An App implements the Model Context Protocol (MCP) via Server-Sent Events (SSE). This allows AI agents to deploy applications directly without writing HTTP calls.

Endpoint

/mcp

How It Works

Your AI tool connects to the MCP endpoint via SSE transport.
The tool discovers available tools via tools/list.
The agent calls deploy_asset with HTML, Markdown, or Mermaid content.
Host An App returns a live URL the agent can share with the user.

MCP Setup Guides

Connect Host An App to your preferred AI tool in one step.

Claude Code

Terminal

claude mcp add --transport http hostan https://hostan.app/mcp

Cursor Editor

Add to .cursor/mcp.json:

JSON

{
  "mcpServers": {
    "hostan": {
      "url": "https://hostan.app/mcp"
    }
  }
}

VS Code

Add to .vscode/mcp.json:

JSON

{
  "servers": {
    "hostan": {
      "type": "http",
      "url": "https://hostan.app/mcp"
    }
  }
}

Generic MCP Client

Use the SSE transport to connect:

Connection

SSE URL:    https://hostan.app/mcp
Transport:  SSE (Server-Sent Events)
Protocol:   JSON-RPC 2.0

deploy_asset Tool

TOOL

The single MCP tool exposed by Host An App. Deploys HTML, Markdown, or Mermaid diagram content and returns a public URL.

Input Schema

parameters

{
  "content": "<!DOCTYPE html>...",   // required, HTML, Markdown, or Mermaid
  "type": "mermaid",             // optional, "html" (default), "markdown", or "mermaid"
  "requested_slug": "my-app",  // optional (alias: "name")
  "title": "My Page",            // optional, page title (markdown/mermaid)
  "one_time": true               // optional, self-destructs after first visit
}

Output

response

{
  "url": "https://hostan.app/my-app",
  "expires_at": "2026-06-17T20:00:00Z"
}

Limits & Rules

Limit	Value
Max payload size	1 MB
Slug length	3–63 chars
Slug characters	a-z 0-9 -
Deploy rate limit	10/min/IP
Deployment TTL	7 days

Reserved Slugs

These names cannot be used as deployment slugs:

api www mcp admin static hostan app _healthz healthz docs assets

Security

Response Headers

All deployment responses include:

X-Content-Type-Options: nosniff
Referrer-Policy: no-referrer

Path Traversal Prevention

All slugs are sanitized before filesystem operations.

No Restrictive CSP

Currently allows arbitrary user JavaScript in deployments. Isolation is at the origin level via same-origin policy.