Cran Extrachecks

CRAN Extra Checks

Help R package developers prepare packages for CRAN submission by systematically checking for common ad-hoc requirements that CRAN reviewers enforce but devtools::check() doesn't catch.

Workflow

1. Initial Assessment: Ask user if this is first submission or resubmission
2. Run Standard Checklist: Work through each item systematically (see below)
3. Identify Issues: As you review files, note specific problems
4. Propose Fixes: Suggest specific changes for each issue found
5. Implement Changes: Make edits only when user approves
6. Verify: Confirm all changes are complete

Standard CRAN Preparation Checklist

Work through these items systematically:

1. Create NEWS.md: Run usethis::use_news_md() if not already present
2. Create cran-comments.md: Run usethis::use_cran_comments() if not already present
3. Review README:
   • Ensure it includes install instructions that will be valid when the package is accepted to CRAN (usually install.packages("pkgname")).
   • Check that it does not contain relative links. This works on GitHub but will be flagged by CRAN. Use full URLs to package documentation or remove the links.
   • Does the README clearly explain the package purpose and functionality?
   • Important: If README.Rmd exists, edit ONLY README.Rmd (README.md will be overwritten), then run devtools::build_readme() to re-render README.md
4. Proofread DESCRIPTION: Carefully review Title: and Description: fields (see detailed guidance below)
5. Check function documentation: Verify all exported functions have @return and @examples (see detailed guidance below)
6. Verify copyright holder: Check that Authors@R: includes a copyright holder with role [cph]
7. Review bundled file licensing: Check licensing of any included third-party files
8. Run URL checks: Use urlchecker::url_check() and fix any issues

Detailed CRAN Checks

Documentation Requirements

Return Value Documentation (Strictly Enforced)

CRAN now strictly requires @return documentation for all exported functions. Use the roxygen2 tag @return to document what the function returns.

• Required even for functions marked @keywords internal
• Required even if function returns nothing - document as @return None or similar
• Must be present for every exported function

Example:

# Missing @return - WILL BE REJECTED
#' Calculate sum
#' @export
my_sum <- function(x, y) {
  x + y
}

# Correct - includes @return
#' Calculate sum
#' @param x First number
#' @param y Second number
#' @return A numeric value
#' @export
my_sum <- function(x, y) {
  x + y
}

# For functions with no return value
#' Print message
#' @param msg Message to print
#' @return None, called for side effects
#' @export
print_msg <- function(msg) {
  cat(msg, "\n")
}

Examples for Exported Functions

If your exported function has a meaningful return value, it will almost definitely require an @examples section. Use the roxygen2 tag @examples.

• Required even for functions marked @keywords internal
• Exceptions exist for functions used purely for side effects (e.g., creating directories)
• Examples must be executable

Un-exported Functions with Examples

If you write roxygen examples for un-exported functions, you must either:

1. Call them with ::: notation: pkg:::my_fun()
2. Use @noRd tag to suppress .Rd file creation

Using \dontrun{} Sparingly

\dontrun{} should only be used if the example really cannot be executed (e.g., missing additional software, API keys, etc.).

• If showing an error, wrap the call in try() instead
• Consider custom predicates (e.g., googlesheets4::sheets_has_token()) with if () blocks
• Sometimes interactive() can be used as the condition
• Lengthy examples (> 5 sec) can use \donttest{}

Never Comment Out Code in Examples

# BAD - Will be rejected
#' @examples
#' # my_function(x)  # Don't do this!

CRAN's guidance: "Examples/code lines in examples should never be commented out. Ideally find toy examples that can be regularly executed and checked."

Guarding Examples with Suggested Packages

Use @examplesIf for entire example sections requiring suggested packages:

#' @examplesIf rlang::is_installed("dplyr")
#' library(dplyr)
#' my_data %>% my_function()

For individual code blocks within examples:

#' @examples
#' if (rlang::is_installed("dplyr")) {
#'   library(dplyr)
#'   my_data %>% my_function()
#' }

DESCRIPTION Title Field

CRAN enforces strict Title requirements:

Use Title Case

Capitalize all words except articles like 'a', 'the'. Use tools::toTitleCase() to help format.

Avoid Redundancy

Common phrases that get flagged:

• "A Toolkit for" → Remove
• "Tools for" → Remove
• "for R" → Remove

Examples:

# BAD
Title: A Toolkit for the Construction of Modeling Packages for R

# GOOD
Title: Construct Modeling Packages

# BAD
Title: Command Argument Parsing for R

# GOOD
Title: Command Argument Parsing

Quote Software/Package Names

Put all software and R package names in single quotes:

# GOOD
Title: Interface to 'Tiingo' Stock Price API

Length Limit

Keep titles under 65 characters.

DESCRIPTION Description Field

Never Start With Forbidden Phrases

CRAN will reject descriptions starting with:

• "This package"
• Package name
• "Functions for"

# BAD
Description: This package provides functions for rendering slides.
Description: Functions for rendering slides to different formats.

# GOOD
Description: Render slides to different formats including HTML and PDF.

Expand to 3-4 Sentences

Single-sentence descriptions are insufficient. Provide a broader description of:

• What the package does
• Why it may be useful
• Types of problems it helps solve

# BAD (too short)
Description: Render slides to different formats.

# GOOD
Description: Render slides to different formats including HTML and PDF.
    Supports custom themes and progressive disclosure patterns. Integrates
    with 'reveal.js' for interactive presentations. Designed for technical
    presentations and teaching materials.

Quote Software Names, Not Functions

# BAD
Description: Uses 'case_when()' to process data.

# GOOD
Description: Uses case_when() to process data with 'dplyr'.

Software, package, and API names get single quotes (including 'R'). Function names do not.

Expand All Acronyms

All acronyms must be fully expanded on first mention:

# BAD
Description: Implements X-SAMPA processing.

# GOOD
Description: Implements Extended Speech Assessment Methods Phonetic
    Alphabet (X-SAMPA) processing.

Publication Titles Only in Double Quotes

Only use double quotes for publication titles, not for phrases or emphasis:

# BAD
Description: Handles dates like "the first Monday of December".

# GOOD
Description: Handles dates like the first Monday of December.

URL and Link Validation

All URLs Must Use HTTPS

CRAN requires https:// protocol for all URLs. HTTP links will be rejected.

# BAD
URL: http://paleobiodb.org/

# GOOD
URL: https://paleobiodb.org/

No Redirecting URLs

CRAN rejects URLs that redirect to other locations. Example rejection:

Found the following (possibly) invalid URLs:
URL: https://h3geo.org/docs/core-library/coordsystems#faceijk-coordinates
     (moved to https://h3geo.org/docs/core-library/coordsystems/)

Use urlchecker Package

# Find redirecting URLs
urlchecker::url_check()

# Automatically update to final destinations
urlchecker::url_update()

Ignore URLs That Will Exist After Publication

Some URLs that don't currently resolve will exist once the package is published on CRAN. These should NOT be changed:

• CRAN badge URLs (e.g., https://cran.r-project.org/package=pkgname)
• CRAN status badges (e.g., https://www.r-pkg.org/badges/version/pkgname)
• CRAN check results (e.g., https://cranchecks.info/badges/pkgname)
• Package documentation URLs on r-universe or pkgdown sites that deploy after release

When urlchecker::url_check() flags these URLs, leave them as-is. They are aspirational URLs that will work once the package is on CRAN.

Check for Invalid File URIs

Relative links in README must exist after package build. Common issue:

Found the following (possibly) invalid file URI:
     URI: CODE_OF_CONDUCT.md
       From: README.md

This occurs when files are in .Rbuildignore. Solutions:

1. Remove file from .Rbuildignore
2. Use usethis::use_code_of_conduct() which generates sections without relative links