diff --git a/NAMESPACE b/NAMESPACE
index bf7b513..26fd980 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -2,4 +2,5 @@
 
 export(mcp_server)
 export(mcp_session)
+export(mcp_set_tools)
 import(rlang)
diff --git a/R/tools.R b/R/tools.R
index d58b89a..6426081 100644
--- a/R/tools.R
+++ b/R/tools.R
@@ -1,3 +1,75 @@
+#' Set the tools available to run in your R session
+#'
+#' @description
+#' By default, acquaint supplies tools from [btw::btw_tools()] to allow clients
+#' to peruse package documentation, inspect your global environment, and query
+#' session details. This function allows you register any tools created with
+#' [ellmer::tool()] instead.
+#'
+#' A call to this function must be placed in your `.Rprofile` and the client
+#' (i.e. Claude Desktop or Claude Code) restarted in order for the new tools
+#' to be registered.
+#'
+#' acquaint will always register the tools "list_r_sessions" and
+#' "select_r_session" in addition to the tools provided here; those tool names
+#' are thus reserved for the package.
+#'
+#' @param x A list of tools created with [ellmer::tool()]. Any list that could
+#' be passed to `chat$set_tools()` can be passed here.
+#'
+#' @returns
+#' `x`, invisibly. Called for side effects. The function will error if `x` is
+#' not a list of `ellmer::ToolDef` objects or if any tool name is one of the
+#' reserved names "list_r_sessions" or "select_r_session".
+#'
+#' @examples
+#' library(ellmer)
+#'
+#' tool_rnorm <- tool(
+#'   rnorm,
+#'   "Draw numbers from a random normal distribution",
+#'   n = type_integer("The number of observations. Must be a positive integer."),
+#'   mean = type_number("The mean value of the distribution."),
+#'   sd = type_number("The standard deviation of the distribution. Must be a non-negative number.")
+#' )
+#'
+#' # supply only one tool, tool_rnorm
+#' mcp_set_tools(list(tool_rnorm))
+#'
+#' # supply both tool_rnorm and `btw_tools()`
+#' mcp_set_tools(c(list(tool_rnorm), btw::btw_tools()))
+#' @export
+mcp_set_tools <- function(x) {
+  check_acquaint_tools(x)
+
+  options(.acquaint_tools = x)
+
+  invisible(x)
+}
+
+check_acquaint_tools <- function(x, call = caller_env()) {
+  if (!is_list(x) || !all(vapply(x, inherits, logical(1), "ellmer::ToolDef"))) {
+    msg <- "{.arg x} must be a list of tools created with {.fn ellmer::tool}."
+    if (inherits(x, "ellmer::ToolDef")) {
+      msg <- c(msg, "i" = "Did you mean to wrap {.arg x} in `list()`?")
+    }
+    cli::cli_abort(msg, call = call)
+  }
+
+  if (
+    any(
+      vapply(x, \(.x) .x@name, character(1)) %in%
+        c("list_r_sessions", "select_r_session")
+    )
+  ) {
+    cli::cli_abort(
+      "The tool names {.field list_r_sessions} and {.field select_r_session} are 
+       reserved by {.pkg acquaint}.",
+      call = call
+    )
+  }
+}
+
 # These two functions are supplied to the client as tools and allow the client
 # to discover R sessions which have called `acquaint::mcp_session()`. They
 # are "model-facing" rather than user-facing.
@@ -77,7 +149,7 @@ select_r_session_tool <-
 
 get_acquaint_tools <- function() {
   res <- c(
-    btw::btw_tools(),
+    getOption(".acquaint_tools", default = btw::btw_tools()),
     list(
       list_r_sessions_tool,
       select_r_session_tool
diff --git a/man/mcp_set_tools.Rd b/man/mcp_set_tools.Rd
new file mode 100644
index 0000000..4253b2c
--- /dev/null
+++ b/man/mcp_set_tools.Rd
@@ -0,0 +1,48 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/tools.R
+\name{mcp_set_tools}
+\alias{mcp_set_tools}
+\title{Set the tools available to run in your R session}
+\usage{
+mcp_set_tools(x)
+}
+\arguments{
+\item{x}{A list of tools created with \code{\link[ellmer:tool]{ellmer::tool()}}. Any list that could
+be passed to \code{chat$set_tools()} can be passed here.}
+}
+\value{
+\code{x}, invisibly. Called for side effects. The function will error if \code{x} is
+not a list of \code{ellmer::ToolDef} objects or if any tool name is one of the
+reserved names "list_r_sessions" or "select_r_session".
+}
+\description{
+By default, acquaint supplies tools from \code{\link[btw:btw_tools]{btw::btw_tools()}} to allow clients
+to peruse package documentation, inspect your global environment, and query
+session details. This function allows you register any tools created with
+\code{\link[ellmer:tool]{ellmer::tool()}} instead.
+
+A call to this function must be placed in your \code{.Rprofile} and the client
+(i.e. Claude Desktop or Claude Code) restarted in order for the new tools
+to be registered.
+
+acquaint will always register the tools "list_r_sessions" and
+"select_r_session" in addition to the tools provided here; those tool names
+are thus reserved for the package.
+}
+\examples{
+library(ellmer)
+
+tool_rnorm <- tool(
+  rnorm,
+  "Draw numbers from a random normal distribution",
+  n = type_integer("The number of observations. Must be a positive integer."),
+  mean = type_number("The mean value of the distribution."),
+  sd = type_number("The standard deviation of the distribution. Must be a non-negative number.")
+)
+
+# supply only one tool, tool_rnorm
+mcp_set_tools(list(tool_rnorm))
+
+# supply both tool_rnorm and `btw_tools()`
+mcp_set_tools(c(list(tool_rnorm), btw::btw_tools()))
+}
diff --git a/tests/testthat/_snaps/tools.md b/tests/testthat/_snaps/tools.md
new file mode 100644
index 0000000..07060fa
--- /dev/null
+++ b/tests/testthat/_snaps/tools.md
@@ -0,0 +1,25 @@
+# mcp_set_tools works
+
+    Code
+      mcp_set_tools("boop")
+    Condition
+      Error in `mcp_set_tools()`:
+      ! `x` must be a list of tools created with `ellmer::tool()`.
+
+---
+
+    Code
+      mcp_set_tools(tool_rnorm)
+    Condition
+      Error in `mcp_set_tools()`:
+      ! `x` must be a list of tools created with `ellmer::tool()`.
+      i Did you mean to wrap `x` in `list()`?
+
+---
+
+    Code
+      mcp_set_tools(list(tool_rnorm))
+    Condition
+      Error in `mcp_set_tools()`:
+      ! The tool names list_r_sessions and select_r_session are reserved by acquaint.
+
diff --git a/tests/testthat/test-tools.R b/tests/testthat/test-tools.R
new file mode 100644
index 0000000..d8cbd84
--- /dev/null
+++ b/tests/testthat/test-tools.R
@@ -0,0 +1,33 @@
+test_that("mcp_set_tools works", {
+  old_option <- getOption("acquaint_tools")
+  on.exit(options(.acquaint_tools = old_option))
+
+  # must be a list
+  expect_snapshot(error = TRUE, mcp_set_tools("boop"))
+
+  tool_rnorm <- ellmer::tool(
+    rnorm,
+    "Draw numbers from a random normal distribution",
+    n = ellmer::type_integer(
+      "The number of observations. Must be a positive integer."
+    ),
+    mean = ellmer::type_number("The mean value of the distribution."),
+    sd = ellmer::type_number(
+      "The standard deviation of the distribution. Must be a non-negative number."
+    )
+  )
+  tool_rnorm_list <- list(tool_rnorm)
+
+  # tools themselves need to be in a list
+  expect_snapshot(error = TRUE, mcp_set_tools(tool_rnorm))
+
+  # uses reserved name
+  tool_rnorm@name <- "list_r_sessions"
+  expect_snapshot(error = TRUE, mcp_set_tools(list(tool_rnorm)))
+
+  expect_equal(mcp_set_tools(tool_rnorm_list), tool_rnorm_list)
+  expect_equal(
+    names(get_acquaint_tools()),
+    c("rnorm", "list_r_sessions", "select_r_session")
+  )
+})