diff --git a/.Rbuildignore b/.Rbuildignore
index d887369..d2566db 100644
--- a/.Rbuildignore
+++ b/.Rbuildignore
@@ -2,5 +2,8 @@
 ^\.Rproj\.user$
 ^LICENSE\.md$
 ^README\.Rmd$
+^scratch$
 ^gitpins$
 ^\.github$
+^.lintr$
+^gitpins_.*$
diff --git a/.gitignore b/.gitignore
index 623d753..01a813a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,5 +5,6 @@
 .DS_Store
 
 # Manual additions
+/scratch/
 /gitpins/
 /gitpins_*/
diff --git a/.lintr b/.lintr
new file mode 100644
index 0000000..fcfdc4f
--- /dev/null
+++ b/.lintr
@@ -0,0 +1,9 @@
+linters: linters_with_defaults(
+    infix_spaces_linter  = NULL, # 40
+    line_length_linter   = NULL, # 13
+    spaces_inside_linter = NULL, # 9
+    object_name_linter   = NULL  # 5
+  )
+exclusions: list(
+    "man/*.Rd"
+  )
diff --git a/DESCRIPTION b/DESCRIPTION
index 6a3298a..2b2f093 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: gitpins
 Type: Package
 Title: Pin urls to local file and version with git
-Version: 0.1.3
+Version: 0.1.3.9001
 Author: Magnus Thor Torfason
 Maintainer: Magnus Thor Torfason <m@zulutime.net>
 Description: Pin URLs to local file and version the pins with git. 
@@ -16,7 +16,8 @@ Imports:
     digest,
     gert,
     here,
-    jsonlite
+    jsonlite,
+    checkmate
 Suggests: 
     tibble,
     testthat (>= 3.0.0),
@@ -25,6 +26,6 @@ Suggests:
 Depends:
     R (>= 4.1.0)
 Config/testthat/edition: 3
-RoxygenNote: 7.1.2
+RoxygenNote: 7.2.3
 URL: https://github.com/torfason/gitpins
 BugReports: https://github.com/torfason/gitpins/issues
diff --git a/NAMESPACE b/NAMESPACE
index 96f28e1..f581cf6 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -3,3 +3,8 @@
 export(gitpin)
 export(list_pins)
 export(pin)
+importFrom(checkmate,assert_flag)
+importFrom(checkmate,assert_int)
+importFrom(checkmate,assert_number)
+importFrom(checkmate,assert_posixct)
+importFrom(checkmate,assert_string)
diff --git a/R/0_gitpins-package.R b/R/0_gitpins-package.R
index 2ab9787..f351e38 100644
--- a/R/0_gitpins-package.R
+++ b/R/0_gitpins-package.R
@@ -16,6 +16,12 @@
 #' To get started, check out the help for the [gitpin()] function, or take a
 #' look at the info on GitHub (see links below).
 #'
+#' @importFrom checkmate assert_string
+#' @importFrom checkmate assert_number
+#' @importFrom checkmate assert_flag
+#' @importFrom checkmate assert_int
+#' @importFrom checkmate assert_posixct
+#'
 #' @docType package
 #' @name gitpins
 #' @md
diff --git a/R/gitpin.R b/R/gitpin.R
index 530204e..e5813cf 100644
--- a/R/gitpin.R
+++ b/R/gitpin.R
@@ -4,11 +4,14 @@
 #' Convert date-time variable to sub-millisecond timestamp
 #'
 #' @param the_datetime a date variable
-#' @return a character representation of `the_datetime` as a sub-millisecond timestamp
+#' @return a character representation of `the_datetime` as a sub-millisecond
+#'   timestamp
 #' @md
 #' @keywords internal
 tstamp <- function(the_datetime) {
-  strftime(the_datetime , "%Y-%m-%d %H:%M:%OS5")
+  assert_posixct(the_datetime)
+
+  strftime(the_datetime, "%Y-%m-%d %H:%M:%OS5")
 }
 
 #' Convert date-time variable to file-compatible timestamp
@@ -19,7 +22,9 @@ tstamp <- function(the_datetime) {
 #' @md
 #' @keywords internal
 fstamp <- function(the_datetime) {
-  strftime(the_datetime , "%Y-%m-%d.%H%M%S")
+  assert_posixct(the_datetime)
+
+  strftime(the_datetime, "%Y-%m-%d.%H%M%S")
 }
 
 #' Initialize gitpins repository
@@ -53,7 +58,8 @@ init_gitpins <- function() {
 #' @md
 #' @export
 pin <- function(url, refresh_hours=12) {
-  #url <- "https://raw.githubusercontent.com/vincentarelbundock/Rdatasets/master/csv/boot/acme.csv"
+  assert_string(url)
+  assert_number(refresh_hours)
 
   # Default frequency of downloads, configurable with config_gitpins()
   # could be to redownload if not the same day as the last download.
@@ -64,16 +70,17 @@ pin <- function(url, refresh_hours=12) {
   stopifnot(!is.null(url) && is.character(url) && length(url)==1)
   url_hash <- digest::digest(url)
   timestamp <-  Sys.time()
-  destfile_data <- file.path(.globals$repo,paste0(url_hash,".data"))
-  destfile_temp <- file.path(.globals$repo,paste0(url_hash,".temp"))
-  on.exit(if(file.exists(destfile_temp))file.remove(destfile_temp))
-  destfile_info <- file.path(.globals$repo,paste0(url_hash,".info"))
-  destfile_json <- file.path(.globals$repo,paste0(url_hash,".json"))
+  destfile_data <- file.path(.globals$repo, paste0(url_hash, ".data"))
+  destfile_temp <- file.path(.globals$repo, paste0(url_hash, ".temp"))
+  on.exit(if (file.exists(destfile_temp)) file.remove(destfile_temp)) # nolint
+  destfile_json <- file.path(.globals$repo, paste0(url_hash, ".json"))
 
   # Read some metadata, to determine what to do next
   if ( file.exists(destfile_json) ) {
     meta_last <- readLines(destfile_json) |> jsonlite::fromJSON()
-    delta_hours <- as.double(difftime(timestamp, as.POSIXct(meta_last$timestamp), units="hours"))
+    delta_hours <- as.double(difftime(timestamp,
+                             as.POSIXct(meta_last$timestamp),
+                             units="hours"))
     if ( delta_hours < refresh_hours ) {
       recent_version_found <- TRUE
     }
@@ -84,16 +91,16 @@ pin <- function(url, refresh_hours=12) {
 
   # Do the download and determine next steps
   if ( recent_version_found ) {
-    message(paste("Recent version found, using it ..."))
+    message(paste("pin() found recent version, using it ..."))
   } else {
 
     tryCatch(
-      { dl_result <- curl::curl_download(url, destfile_temp, quiet=TRUE) },
-        error=function(e) {},
-        warning=function(e) {}
+      { curl::curl_download(url, destfile_temp, quiet=TRUE) },
+        error=function(e) {},     # nolint
+        warning=function(e) {}    # nolint
     )
 
-    if ( !file.exists(destfile_temp) || file.size(destfile_temp)==0) {
+    if ( !file.exists(destfile_temp) || file.size(destfile_temp)==0 ) {
       # Download failed in some way
       if (!file.exists(destfile_data)) {
         stop("Download failed and no earlier version found: Aborting!")
@@ -106,13 +113,12 @@ pin <- function(url, refresh_hours=12) {
     # Download succeeded
     message("Downloaded fresh version ...")
     file.copy(destfile_temp, destfile_data, overwrite = TRUE)
-    #writeLines(c(timestamp, url), destfile_info)
     list(timestamp=jsonlite::unbox(tstamp(timestamp)), url=jsonlite::unbox(url)) |>
       jsonlite::toJSON(pretty = TRUE, simplifyVector=TRUE) |>
       writeLines(destfile_json)
 
     gert::git_add(
-      basename(c(destfile_data,destfile_json)), # Must be relative to repo root
+      basename(c(destfile_data, destfile_json)), # Must be relative to repo root
       repo=.globals$repo)
     gert::git_commit_all(paste0("[", tstamp(timestamp), "] ", url), repo=.globals$repo)
   }
@@ -138,6 +144,8 @@ gitpin <- pin
 #' @md
 #' @export
 list_pins <- function(history=FALSE) {
+  assert_flag(history)
+
   init_gitpins()
 
   # Function to return empty data.frame on fresh repo instead of erroring
@@ -157,19 +165,19 @@ list_pins <- function(history=FALSE) {
       lapply(as.data.frame) |>
       do.call(what=rbind)
     if (is.null(d.result)) d.result <- data.frame(timestamp=character(), url=character())
-    d.result <- d.result[order(d.result$timestamp, decreasing=TRUE),]
+    d.result <- d.result[order(d.result$timestamp, decreasing=TRUE), ]
   } else {
     # Return result based on what is in the gitlog
     logmessages <- get_repo_log_messages()
     d.result <- data.frame(
-      timestamp = gsub('\\[(.*)\\].*','\\1',logmessages),
-      url = gsub('.*\\] (.*)','\\1',logmessages) |>
+      timestamp = gsub("\\[(.*)\\].*", "\\1", logmessages),
+      url = gsub(".*\\] (.*)", "\\1", logmessages) |>
         sub(pattern="\\n", replacement="")
     )
   }
 
   # Be nice and return a tibble if it is available
-  if (requireNamespace("tibble")){
+  if (requireNamespace("tibble")) {
     d.result <- tibble::as_tibble(d.result)
   }
   d.result
@@ -181,4 +189,3 @@ list_pins <- function(history=FALSE) {
 clear_old_pins <- function() {
   stop("not implemented")
 }
-
diff --git a/build/build_and_release_process.R b/build/build_and_release_process.R
index 06c8ac5..b7fdf72 100644
--- a/build/build_and_release_process.R
+++ b/build/build_and_release_process.R
@@ -3,7 +3,7 @@
 {
   gpdir <- here::here("gitpins")
   if (file.exists(gpdir)) {
-    file.rename(gpdir, paste0(gpdir,"_",fstamp(Sys.time())))
+    file.rename(gpdir, paste0(gpdir,"_",gitpins:::fstamp(Sys.time())))
   }
   devtools::build()
   devtools::document()
diff --git a/inst/WORDLIST b/inst/WORDLIST
index e2e42e0..861c7d0 100644
--- a/inst/WORDLIST
+++ b/inst/WORDLIST
@@ -1,3 +1,4 @@
+CMD
+api
 borked
 deduplication
-CMD
diff --git a/man/tstamp.Rd b/man/tstamp.Rd
index 7590ef9..fe14a46 100644
--- a/man/tstamp.Rd
+++ b/man/tstamp.Rd
@@ -10,7 +10,8 @@ tstamp(the_datetime)
 \item{the_datetime}{a date variable}
 }
 \value{
-a character representation of \code{the_datetime} as a sub-millisecond timestamp
+a character representation of \code{the_datetime} as a sub-millisecond
+timestamp
 }
 \description{
 Convert date-time variable to sub-millisecond timestamp
diff --git a/tests/testthat/test-gitpin-local.R b/tests/testthat/test-gitpin-local.R
index 1a76a91..a3fb93f 100644
--- a/tests/testthat/test-gitpin-local.R
+++ b/tests/testthat/test-gitpin-local.R
@@ -1,23 +1,24 @@
 
-test_that("gitpins work with local server",{
+test_that("gitpins work with local server", {
 
   # Skip test if suggested packages callr and servr are not installed
   if ( !requireNamespace("callr", quietly = TRUE) ||
        !requireNamespace("servr", quietly = TRUE) ) {
-    skip()
+    skip("Packages callr or servr not found, skipping test")
   }
 
   # Set here with reference to the test file
   here::i_am("tests/testthat/test-gitpin-local.R") |> expect_message("gitpins")
 
   # If here does not get us the path to the local www_root, we panic
-  if(!file.exists(here::here("tests","www_root"))) stop("Web root not found, skipping test")
+  if (!file.exists(here::here("tests", "www_root")))
+    stop("Web root not found, skipping test")
 
   # Function to start a local server.
   callr_servr <- function() {
     host    <- getOption("servr.host", "127.0.0.1")
     port    <- servr:::random_port()
-    dir     <- here::here("tests","www_root")
+    dir     <- here::here("tests", "www_root")
     proc <- callr::r_bg(servr::httd,
                         args=list(daemon=FALSE, dir=dir, host=host, port=port),
                         package="servr")
@@ -75,4 +76,3 @@ test_that("gitpins work with local server",{
     "Download failed, using last good version ...")
 
 })
-
diff --git a/tests/testthat/test-gitpin-remote.R b/tests/testthat/test-gitpin-remote.R
index 4b2106c..623a142 100644
--- a/tests/testthat/test-gitpin-remote.R
+++ b/tests/testthat/test-gitpin-remote.R
@@ -1,5 +1,5 @@
 
-test_that("gitpin works with remote URLs",{
+test_that("gitpin works with remote URLs", {
 
   skip_if_offline()
 
diff --git a/tests/testthat/test-list_gitpins.R b/tests/testthat/test-list_gitpins.R
index d8a36d7..9630d2a 100644
--- a/tests/testthat/test-list_gitpins.R
+++ b/tests/testthat/test-list_gitpins.R
@@ -25,7 +25,7 @@ test_that("listing is in default order", {
 
   # Nohist should be subset of hist
   matches <- listing_hist$timestamp %in% listing_nohist$timestamp
-  listing_hist_subset <- listing_hist[matches,]
+  listing_hist_subset <- listing_hist[matches, ]
   expect_equal(listing_hist_subset, listing_nohist)
 
 })