diff --git a/.github/workflows/check.yaml b/.github/workflows/check.yaml
index e439754..bb1194f 100644
--- a/.github/workflows/check.yaml
+++ b/.github/workflows/check.yaml
@@ -1,8 +1,4 @@
-on:
-  push:
-    branches: [main]
-  pull_request:
-    branches: [main]
+on: [push, pull_request]
 
 name: check
 
diff --git a/.github/workflows/lint.yaml b/.github/workflows/lint.yaml
index c2e6d0b..a3f3f23 100644
--- a/.github/workflows/lint.yaml
+++ b/.github/workflows/lint.yaml
@@ -1,8 +1,4 @@
-on:
-  push:
-    branches: [main]
-  pull_request:
-    branches: [main]
+on: [push, pull_request]
 
 name: lint
 
diff --git a/DESCRIPTION b/DESCRIPTION
index 808ad85..4fce850 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: r.releases.utils
 Title: Utilities for An R Universe of Package Releases
 Description: Utilities for an R universe of package releases.
-Version: 0.0.2.9000
+Version: 0.0.3
 License: MIT + file LICENSE
 URL:
   https://r-releases.github.io/r.releases.utils/,
@@ -32,7 +32,8 @@ Imports:
   gh,
   jsonlite,
   nanonext,
-  pkgsearch
+  pkgsearch,
+  vctrs
 Encoding: UTF-8
 Language: en-US
 Config/testthat/edition: 3
diff --git a/NAMESPACE b/NAMESPACE
index 8551c1b..6bd490d 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -5,7 +5,10 @@ export(assert_package)
 export(build_universe)
 export(review_pull_request)
 export(review_pull_requests)
+export(try_message)
 importFrom(gh,gh)
+importFrom(jsonlite,parse_json)
 importFrom(jsonlite,read_json)
 importFrom(nanonext,parse_url)
 importFrom(pkgsearch,cran_package)
+importFrom(vctrs,vec_rbind)
diff --git a/NEWS.md b/NEWS.md
index baaa2a8..5c5e96c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,8 +1,10 @@
-# r.releases.utils 0.0.2.9000 (development)
+# r.releases.utils 0.0.3
 
 * Checks URL matches the package description for CRAN packages.
 * `check_package()` checks the URL and name directly, not a file.
 * Add more strict URL assertions.
+* Accept custom JSON entries but flag them for manual review.
+* Print progress messages from `build_universe()`.
 
 # r.releases.utils 0.0.2
 
diff --git a/R/assert_package.R b/R/assert_package.R
index b1b42c0..645bbea 100644
--- a/R/assert_package.R
+++ b/R/assert_package.R
@@ -4,10 +4,26 @@
 #' @description Validate a package entry.
 #' @return A character string if there is a problem with the package entry,
 #'   otherwise `NULL` if there are no issues.
-assert_package <- function(name, url) {
-  if (!is_character_scalar(name)) {
+#' @param name Character of length 1, package name.
+#' @param url Usually a character of length 1 with the package URL.
+#'   Can also be a custom JSON string with the package URL and other metadata,
+#'   but this is for rare cases and flags the package for manual review.
+#' @param assert_cran_url Logical of length 1, whether to check
+#'   the alignment between the specified URL and the CRAN URL.
+assert_package <- function(name, url, assert_cran_url = TRUE) {
+  if (!is_package_name(name)) {
     return("Invalid package name.")
   }
+  json <- try(jsonlite::parse_json(json = url), silent = TRUE)
+  if (!inherits(json, "try-error")) {
+    return(
+      paste(
+        "Entry of package",
+        shQuote(name),
+        "looks like custom JSON"
+      )
+    )
+  }
   if (!is_character_scalar(url)) {
     return("Invalid package URL.")
   }
@@ -57,5 +73,14 @@ assert_package <- function(name, url) {
   if (identical(owner, "cran")) {
     return(paste("URL", shQuote(url), "appears to use a CRAN mirror."))
   }
-  assert_cran_url(name = name, url = url)
+  if (assert_cran_url) {
+    return(assert_cran_url(name = name, url = url))
+  }
+}
+
+is_package_name <- function(name) {
+  is_character_scalar(name) && grepl(
+    pattern = "^[a-zA-Z][a-zA-Z0-9.]*[a-zA-Z0-9]$",
+    x = trimws(name)
+  )
 }
diff --git a/R/build_universe.R b/R/build_universe.R
index bc86467..6a2e402 100644
--- a/R/build_universe.R
+++ b/R/build_universe.R
@@ -13,24 +13,87 @@ build_universe <- function(input = getwd(), output = "packages.json") {
   assert_character_scalar(output, "invalid output")
   assert_file(input)
   packages <- list.files(input, all.files = FALSE, full.names = TRUE)
-  contents <- lapply(X = packages, FUN = read_package_entry)
-  out <- data.frame(
-    package = trimws(basename(packages)),
-    url = trimws(unlist(contents, use.names = FALSE)),
-    branch = "*release"
-  )
+  message("Processing ", length(packages), " package entries.")
+  entries <- lapply(X = packages, FUN = read_package_entry)
+  message("Aggregating ", length(entries), " package entries.")
+  aggregated <- do.call(what = vctrs::vec_rbind, args = entries)
   if (!file.exists(dirname(output))) {
     dir.create(dirname(output))
   }
-  jsonlite::write_json(x = out, path = output)
+  message("Writing packages.json.")
+  jsonlite::write_json(x = aggregated, path = output)
   invisible()
 }
 
 read_package_entry <- function(package) {
-  out <- readLines(con = package, warn = FALSE)
-  message <- assert_package(name = basename(package), url = out)
+  message("Processing package entry ", package)
+  name <- trimws(basename(package))
+  lines <- readLines(con = package, warn = FALSE)
+  out <- try(jsonlite::parse_json(lines), silent = TRUE)
+  if (inherits(out, "try-error")) {
+    package_entry_url(name = name, url = lines)
+  } else {
+    package_entry_json(name = name, json = out)
+  }
+}
+
+package_entry_url <- function(name, url) {
+  message <- assert_package(
+    name = name,
+    url = url,
+    assert_cran_url = FALSE # Prevents massive slowdown from 20000+ packages.
+  )
   if (!is.null(message)) {
     stop(message, call. = FALSE)
   }
-  out
+  data.frame(
+    package = trimws(name),
+    url = trimws(url),
+    branch = "*release"
+  )
+}
+
+package_entry_json <- function(name, json) {
+  fields <- names(json)
+  good_fields <- identical(
+    sort(fields),
+    sort(c("package", "url", "branch", "subdir"))
+  )
+  if (!good_fields) {
+    stop(
+      "Custom JSON entry for package ",
+      shQuote(name),
+      " must have fields 'packages', 'url', 'branch', and 'subdir' ",
+      "and no other fields.",
+      call. = FALSE
+    )
+  }
+  if (!identical(name, json$package)) {
+    stop(
+      "The 'packages' field disagrees with the package name ",
+      shQuote(name),
+      call. = FALSE
+    )
+  }
+  if (!identical(json$branch, "*release")) {
+    stop(
+      "The 'branch' field of package ",
+      shQuote(name),
+      "is not \"*release\".",
+      call. = FALSE
+    )
+  }
+  for (field in names(json)) {
+    assert_character_scalar(
+      x = json[[field]],
+      message = paste(
+        "Invalid value in field",
+        shQuote(field),
+        "in the JSON entry for package name",
+        shQuote(name)
+      )
+    )
+    json[[field]] <- trimws(json[[field]])
+  }
+  as.data.frame(json)
 }
diff --git a/R/package.R b/R/package.R
index aac3edc..704c66f 100644
--- a/R/package.R
+++ b/R/package.R
@@ -3,7 +3,8 @@
 #' @name r.releases.utils-package
 #' @family help
 #' @importFrom gh gh
-#' @importFrom jsonlite read_json
+#' @importFrom jsonlite parse_json read_json
 #' @importFrom nanonext parse_url
 #' @importFrom pkgsearch cran_package
+#' @importFrom vctrs vec_rbind
 NULL
diff --git a/R/review_pull_request.R b/R/review_pull_request.R
index bb5441d..ea51ada 100644
--- a/R/review_pull_request.R
+++ b/R/review_pull_request.R
@@ -8,6 +8,7 @@
 #'   2. Add a bad URL (manual review).
 #'   3. Change a URL (manual review).
 #'   4. Add a file in a forbidden place (close).
+#'   5. Add a custom JSON file which can be parsed (manual review).
 #' @return `NULL` (invisibly).
 #' @param owner Character of length 1, name of the universe repository owner.
 #' @param repo Character of length 1, name of the universe repository.
diff --git a/R/utils_assert.R b/R/utils_assert.R
index 05cd20f..c722ede 100644
--- a/R/utils_assert.R
+++ b/R/utils_assert.R
@@ -30,6 +30,13 @@ is_positive_scalar <- function(x) {
     all(x > 0)
 }
 
+#' @title Get try error message
+#' @export
+#' @keywords internal
+#' @description Get the error message of an error object from `try()`.
+#' @param try_error `try()` error object.
+#' @param collapse Character of length 1, delimiter for the
+#'   lines of the message.
 try_message <- function(try_error, collapse = " ") {
   paste(conditionMessage(attr(try_error, "condition")), collapse = collapse)
 }
diff --git a/README.md b/README.md
index f1416a7..66a5b18 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,6 @@
 [![check](https://github.com/r-releases/r.releases.utils/actions/workflows/check.yaml/badge.svg)](https://github.com/r-releases/r.releases.utils/actions?query=workflow%3Acheck)
 [![lint](https://github.com/r-releases/r.releases.utils/actions/workflows/lint.yaml/badge.svg)](https://github.com/r-releases/r.releases.utils/actions?query=workflow%3Alint)
 
-This R package contains helper functions for the front-end infrastructure to create the `r-releases` `r-universe`. To install it locally, run `install.packages("r.releases.utils", repos = "https://r-releases.r-universe.dev")`.
+`r.releases.utils` is an R package to support automation for the `r-releases` project.
 
-Please report bugs to https://github.com/r-releases/help/issues and send other feedback and questions to https://github.com/r-releases/help/discussions. 
+For all matters please refer to https://github.com/r-releases/help.
diff --git a/man/assert_package.Rd b/man/assert_package.Rd
index 1f13740..9551cca 100644
--- a/man/assert_package.Rd
+++ b/man/assert_package.Rd
@@ -4,7 +4,17 @@
 \alias{assert_package}
 \title{Validate a Package Entry}
 \usage{
-assert_package(name, url)
+assert_package(name, url, assert_cran_url = TRUE)
+}
+\arguments{
+\item{name}{Character of length 1, package name.}
+
+\item{url}{Usually a character of length 1 with the package URL.
+Can also be a custom JSON string with the package URL and other metadata,
+but this is for rare cases and flags the package for manual review.}
+
+\item{assert_cran_url}{Logical of length 1, whether to check
+the alignment between the specified URL and the CRAN URL.}
 }
 \value{
 A character string if there is a problem with the package entry,
diff --git a/man/review_pull_request.Rd b/man/review_pull_request.Rd
index 94b00a2..fb1e8bc 100644
--- a/man/review_pull_request.Rd
+++ b/man/review_pull_request.Rd
@@ -28,6 +28,7 @@ Testing of this function unfortunately needs to be manual. Test cases:
 \item Add a bad URL (manual review).
 \item Change a URL (manual review).
 \item Add a file in a forbidden place (close).
+\item Add a custom JSON file which can be parsed (manual review).
 }
 }
 
diff --git a/man/review_pull_requests.Rd b/man/review_pull_requests.Rd
index e52bbc0..3ee0741 100644
--- a/man/review_pull_requests.Rd
+++ b/man/review_pull_requests.Rd
@@ -25,6 +25,7 @@ Testing of this function unfortunately needs to be manual. Test cases:
 \item Add a bad URL (manual review).
 \item Change a URL (manual review).
 \item Add a file in a forbidden place (close).
+\item Add a custom JSON file which can be parsed (manual review).
 }
 }
 
diff --git a/man/try_message.Rd b/man/try_message.Rd
new file mode 100644
index 0000000..0d9669b
--- /dev/null
+++ b/man/try_message.Rd
@@ -0,0 +1,18 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/utils_assert.R
+\name{try_message}
+\alias{try_message}
+\title{Get try error message}
+\usage{
+try_message(try_error, collapse = " ")
+}
+\arguments{
+\item{try_error}{\code{try()} error object.}
+
+\item{collapse}{Character of length 1, delimiter for the
+lines of the message.}
+}
+\description{
+Get the error message of an error object from \code{try()}.
+}
+\keyword{internal}
diff --git a/tests/test-assert_package.R b/tests/test-assert_package.R
index 3eac478..6048333 100644
--- a/tests/test-assert_package.R
+++ b/tests/test-assert_package.R
@@ -1,30 +1,52 @@
 stopifnot(
   grepl(
     "Invalid package name",
-    r.releases.utils::assert_package(name = letters, url = "x"),
+    r.releases.utils::assert_package(name = letters, url = "xy"),
     fixed = TRUE
   )
 )
 
 stopifnot(
   grepl(
-    "Invalid package URL",
-    r.releases.utils::assert_package(name = "x", url = letters),
+    "Invalid package name",
+    r.releases.utils::assert_package(
+      name = ".gh",
+      url = "https://github.com/r-lib/gh"
+    ),
     fixed = TRUE
   )
 )
 
 stopifnot(
   grepl(
-    "Found invalid package name",
+    "looks like custom JSON",
     r.releases.utils::assert_package(
-      name = ".gh",
-      url = "https://github.com/r-lib/gh"
+      name = "xy",
+      url = "{\"branch\": \"release\"}"
+    ),
+    fixed = TRUE
+  )
+)
+
+stopifnot(
+  grepl(
+    "Invalid package URL",
+    r.releases.utils::assert_package(
+      name = "xy",
+      url = letters
     ),
     fixed = TRUE
   )
 )
 
+stopifnot(
+  grepl(
+    "Invalid package URL",
+    r.releases.utils::assert_package(name = "xy", url = letters),
+    fixed = TRUE
+  )
+)
+
 stopifnot(
   grepl(
     "Found malformed URL",
diff --git a/tests/test-build_universe.R b/tests/test-build_universe.R
index a4b6a2e..5dbc721 100644
--- a/tests/test-build_universe.R
+++ b/tests/test-build_universe.R
@@ -1,3 +1,4 @@
+# Success test case for ordinary URLs.
 packages <- tempfile()
 dir.create(packages)
 writeLines("https://github.com/r-lib/gh", file.path(packages, "gh"))
@@ -24,6 +25,7 @@ stopifnot(identical(json, exp))
 unlink(packages, recursive = TRUE)
 unlink(universe)
 
+# One of the URLs is malformed.
 packages <- tempfile()
 dir.create(packages)
 writeLines("https://github.com/r-lib/gh", file.path(packages, "gh"))
@@ -39,3 +41,130 @@ out <- try(
 stopifnot(inherits(out, "try-error"))
 unlink(packages, recursive = TRUE)
 unlink(universe)
+
+# Acceptable custom JSON.
+packages <- tempfile()
+dir.create(packages)
+writeLines("https://github.com/r-lib/gh", file.path(packages, "gh"))
+writeLines(
+  c(
+    "{",
+    "  \"package\": \"paws.analytics\",",
+    "  \"url\": \"https://github.com/paws-r/paws\",",
+    "  \"subdir\": \"cran/paws.analytics\",",
+    "  \"branch\": \"*release\"",
+    "}"
+  ),
+  file.path(packages, "paws.analytics")
+)
+universe <- file.path(tempfile(), "out")
+r.releases.utils::build_universe(input = packages, output = universe)
+out <- jsonlite::read_json(path = universe)
+exp <- list(
+  list(
+    package = "gh",
+    url = "https://github.com/r-lib/gh",
+    branch = "*release"
+  ),
+  list(
+    package = "paws.analytics",
+    url = "https://github.com/paws-r/paws",
+    branch = "*release",
+    subdir = "cran/paws.analytics"
+  )
+)
+stopifnot(identical(out, exp))
+unlink(packages, recursive = TRUE)
+unlink(universe)
+
+# Missing branch field
+packages <- tempfile()
+dir.create(packages)
+writeLines("https://github.com/r-lib/gh", file.path(packages, "gh"))
+writeLines(
+  c(
+    "{",
+    "  \"package\": \"paws.analytics\",",
+    "  \"url\": \"https://github.com/paws-r/paws\",",
+    "  \"subdir\": \"cran/paws.analytics\"",
+    "}"
+  ),
+  file.path(packages, "paws.analytics")
+)
+universe <- file.path(tempfile(), "out")
+out <- try(
+  r.releases.utils::build_universe(input = packages, output = universe),
+  silent = TRUE
+)
+stopifnot(inherits(out, "try-error"))
+stopifnot(
+  grepl(
+    pattern = "JSON entry for package 'paws.analytics' must have fields",
+    x = r.releases.utils::try_message(out),
+    fixed = TRUE
+  )
+)
+unlink(packages, recursive = TRUE)
+unlink(universe)
+
+# Disagreeing package field
+packages <- tempfile()
+dir.create(packages)
+writeLines("https://github.com/r-lib/gh", file.path(packages, "gh"))
+writeLines(
+  c(
+    "{",
+    "  \"package\": \"paws.analytics2\",",
+    "  \"url\": \"https://github.com/paws-r/paws\",",
+    "  \"subdir\": \"cran/paws.analytics\",",
+    "  \"branch\": \"*release\"",
+    "}"
+  ),
+  file.path(packages, "paws.analytics")
+)
+universe <- file.path(tempfile(), "out")
+out <- try(
+  r.releases.utils::build_universe(input = packages, output = universe),
+  silent = TRUE
+)
+stopifnot(inherits(out, "try-error"))
+stopifnot(
+  grepl(
+    pattern = "The 'packages' field disagrees with the package name",
+    x = r.releases.utils::try_message(out),
+    fixed = TRUE
+  )
+)
+unlink(packages, recursive = TRUE)
+unlink(universe)
+
+# Bad branch field
+packages <- tempfile()
+dir.create(packages)
+writeLines("https://github.com/r-lib/gh", file.path(packages, "gh"))
+writeLines(
+  c(
+    "{",
+    "  \"package\": \"paws.analytics\",",
+    "  \"url\": \"https://github.com/paws-r/paws\",",
+    "  \"subdir\": \"cran/paws.analytics\",",
+    "  \"branch\": \"development\"",
+    "}"
+  ),
+  file.path(packages, "paws.analytics")
+)
+universe <- file.path(tempfile(), "out")
+out <- try(
+  r.releases.utils::build_universe(input = packages, output = universe),
+  silent = TRUE
+)
+stopifnot(inherits(out, "try-error"))
+stopifnot(
+  grepl(
+    pattern = "The 'branch' field of package",
+    x = r.releases.utils::try_message(out),
+    fixed = TRUE
+  )
+)
+unlink(packages, recursive = TRUE)
+unlink(universe)