tooltip on shiny R?

I want to have a tool-tip in my Shiny R application. Is there any easy way to achieve that? For now, I am creating a density map and I want a simple tool-tip showing "click here to slide through years" while hovering the mouse over slider YEAR.

User Interface:

library(shiny)
shinyUI(pageWithSidebar(
  headerPanel("Density Map"),
  sidebarPanel(
	sliderInput("slider_year", "YEAR:", 
				min = 2001, max = 2011, value = 2009, 
				format="####", locale="us"
	)
  )
 ),

  mainPanel(  
	plotOutput("event_heatmap_map", width = "100%", height = "100%")
  )
))

Server Code:

library(shiny)
library(ggmap)
library(ggplot2)
mydata <- read.csv("/var/shiny-server/www/dMetrics.csv")
shinyServer(function(input, output) {
	output$event_heatmap_map <- renderPlot(width = "auto", height = 640,{

		slice_year <- mydata[mydata$YEAR==input$slider_year,]
		map <- get_map(c(lon = -55.3632715, lat = 31.7632836), zoom = 3, source = 'google', maptype = c("terrain"), messaging = FALSE, color = 'color')
		world <- ggmap(map)
		world <- world + stat_density2d(data = slice_year, aes(x = WEST, y = NORTH, fill = ..level.., alpha = ..level..), show_guide = FALSE, geom = "polygon", na.rm = TRUE) + scale_fill_gradient(name="Density", low="maroon", high="yellow", guide = 'colorbar')
		plot(world)
	})
})

Thanks for the help.

I think you should be able to replace this:

sliderInput("slider_year", "YEAR:", 
            min = 2001, max = 2011, value = 2009, 
            format="####", locale="us"
)

with this:

tags$div(title="Click here to slide through years",
    sliderInput("slider_year", "YEAR:", 
                min = 2001, max = 2011, value = 2009, 
                format="####", locale="us"
    )
)

This is slightly easier and more elegant way.

library(shinyBS) # Additional Bootstrap Controls

## From ui.R: Adds a tooltip to element with inputId = "someInput" 
## with text, "This is an input.", that appears to the left on hover.
bsTooltip(id = "someInput", title = "This is an input", 
          placement = "left", trigger = "hover")

## From server.R: Add the same tooltip as above
addTooltip(session, id = "someInput", title = "This is an input.",
           placement = "left", trigger = "hover")

You can add the Tooltip in ui.R or server.R, Additional you can also use Popover.

Nowadays it's possible to wrap ggplot visualizations around plot_ly, and plotly has a native component (precissely named tootip) which will serve the purpose you're looking for:

Example taken from: https://plotly.com/ggplot2/interactive-tooltip/

library(plotly)
#install.packages("gapminder")
library(gapminder)

p <- ggplot(gapminder, aes(x = gdpPercap, y = lifeExp, color = continent, text =      paste("country:", country))) +
     geom_point(alpha = (1/3)) + scale_x_log10()  

fig <- ggplotly(p)

fig

Also, refer to: https://plotly-r.com/controlling-tooltips.html for a more detailed explanation.