Reticle — Claude Code MCP server: what it does, how to install
Verifies running web applications from the inside via MCP tools. The agent navigates, triggers actions, and asserts DOM states without screenshots.
claude mcp add reticle -- npx -y @reticlehq/serverWhat Reticle does
Reticle connects a coding agent directly to a live web application. The bridge hosts a local WebSocket endpoint at ws://localhost:4400, which links to the project's @reticlehq/browser SDK. Instead of relying on image recognition, the agent examines DOM state, inputs text, and observes reactions internally.
By default, the server exposes 10 tools, including reticle_navigate, reticle_look, reticle_act, reticle_observe, and reticle_assert. Only reticle_act_and_wait and reticle_assert return pass-fail verdicts; other tools move or inspect the page. Additional features like network mocking, clock control, and visual diffs stay hidden to keep token usage low. You run them via reticle_run or expose everything at once by setting RETICLE_ADVERTISE_ALL_TOOLS=1, which roughly doubles tool payloads.
The server requires the companion @reticlehq/browser SDK wired into the target application, which you configure via npx @reticlehq/server init.
What it helps with
- test running web apps directly from the inside without screenshots
- execute user interactions like clicks and form inputs via MCP tools
- validate DOM state with explicit verdict returns
- control browser clocks and mock network calls during agent runs
Example prompts for the agent
- Navigate to the settings page and verify the save button using
reticle_assert - Click the submit button and wait for the response using
reticle_act_and_wait - Check what extra tools are available by running
reticle_tools
How to install Reticle
Platform CLI
claude mcp add reticle -- npx -y @reticlehq/serverPlatform CLI
codex mcp add server -- npx -y @reticlehq/serverConfig file
{
"mcpServers": {
"server": {
"command": "npx",
"args": [
"-y",
"@reticlehq/server"
]
}
}
}Config file
{
"servers": {
"server": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"@reticlehq/server"
]
}
}
}Platform CLI
gemini mcp add server npx -y @reticlehq/serverStep by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about Reticle
How to install Reticle in Claude Code?
Run claude mcp add reticle -- npx -y @reticlehq/server in your terminal.
What does Reticle do?
It hosts a WebSocket bridge at ws://localhost:4400 so your coding assistant can navigate, interact with, and assert against your running web app via MCP.
What does RETICLE_ADVERTISE_ALL_TOOLS=1 do?
It reveals extended tools like network mocking and clock control to the agent, though it roughly doubles the per-turn tool payload.
