diff --git a/MetalogDB/README.md b/MetalogDB/README.md
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+# Usage
+
+To use this function download the directory and source the `fetchMetalogTSE.R`
+script. You should now have the function available in your R session.
+
+The function will create a `.data_cache` dir in your working directory if one
+is not present. 
+
+To build a `tse` -object you can call the function like so;
+
+`tse <- fetchMetalogTSE("human", "core")`
+
+It will attempt to download the latest versions of datafiles from the Metalog
+Database and compile them into a TSE.
+
+By default it will use the cache on subsequent calls. 
+
+Available options are;
+
+"human", "animal", "ocean", and "environmental"
+
+It will download the metaphlan4 profiles for these collections.
+
+For metadata options are;
+
+"core", "extended", "all"
+
+Core metadata is available for most, if not all, samples. Extended
+is the partially harmonized metadata set, while "all" downloads all the metadata
+available down to study specific variables. 
+
+You can disable cache with the `use_cache = FALSE` option, this will force
+a download of the latest available datasets. 
+
+Additionally you can use the metalog webUI to explore the samples. This allows
+you to download a samplelist file that you can pass to the function, and 
+it will subset the tse to the selected samples upon creation.
\ No newline at end of file
diff --git a/MetalogDB/fetchMetalogTSE.R b/MetalogDB/fetchMetalogTSE.R
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+# This function downloads metaphlan profiles and associated metadata
+# from the Metalog database. The option exists to filter to a subset
+# if a samplelist is provided, downloaded from the Metalog webUI.
+#
+# Author: Rasmus Hindström
+# Date: ---
+
+# Libraries
+library(Matrix)
+library(TreeSummarizedExperiment)
+library(data.table)
+library(dplyr)
+library(httr)
+
+# -------------
+# Helpers FUNs
+# -------------
+
+# Function to check that inputs to fetchMetalogTSE
+.validate_inputs <- function(collection, metadata, samplelist, use_cache) {
+  allowed_collections <- c("human", "animal", "ocean", "environmental")
+  if (missing(collection) || !collection %in% allowed_collections) {
+    stop(
+      "Validation Error: 'collection' must be one of: ",
+      paste(paste0('""', allowed_collections, '""'), collapse = ", ")
+    )
+  }
+
+  allowed_metadata <- c("core", "extended", "all")
+  if (!metadata %in% allowed_metadata) {
+    stop(
+      "Validation Error: 'metadata' must be one of: ",
+      paste(paste0('""', allowed_metadata, '""'), collapse = ", ")
+    )
+  }
+
+  if (!is.null(samplelist)) {
+    ext <- tolower(tools::file_ext(samplelist))
+    allowed_exts <- c("csv", "tsv", "txt", "json")
+    if (!ext %in% allowed_exts) {
+      stop(
+        "Validation Error: samplelist file type must be one of: ",
+        paste(allowed_exts, collapse = ", ")
+      )
+    }
+  }
+
+  if (!is.logical(use_cache) || length(use_cache) != 1 || is.na(use_cache)) {
+    stop("Validation Error: 'use_cache' must be a single logical value (TRUE or FALSE)")
+  }
+
+  invisible(NULL)
+}
+
+# Function to download datafiles, adapted from Metalog's example script
+# Function to download datafiles, adapted to handle broken HTTP redirects
+.download_if_missing <- function(
+  target_url,
+  download_dir = ".data_cache",
+  use_cache = TRUE
+) {
+  base_filename <- basename(target_url)
+
+  # Caching Logic
+  if (use_cache) {
+    pattern <- sub("latest", "[0-9]{4}-[0-9]{2}-[0-9]{2}", base_filename)
+    matching_files <- list.files(download_dir, pattern = pattern, full.names = TRUE)
+
+    if (length(matching_files) > 0) {
+      latest_file <- max(matching_files)
+      message("Loaded cached file: ", latest_file)
+      return(latest_file)
+    }
+  }
+
+  if (!dir.exists(download_dir)) {
+    dir.create(download_dir, recursive = TRUE, showWarnings = FALSE)
+  }
+
+  message("Fetching file from: ", target_url)
+
+  ### Masquarade as a browser, in case of anti-scraping measures
+  ua <- httr::user_agent("Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36")
+
+  ### Metalog server downgrades protocol from https >> http, 
+  ### Since 1st of April 2026. This janky solution is needed to force https
+
+  # Catch the redirect
+  initial_req <- httr::GET(target_url, ua, httr::config(followlocation = FALSE))
+  
+  # Check if we got a redirect to HTTP
+  if (initial_req$status_code >= 300 && initial_req$status_code < 400) {
+    # Extract the redirected URL
+    final_url <- initial_req$headers$location
+    
+    # Force HTTPS protocol
+    final_url <- sub("^http://", "https://", final_url)
+    message("Intercepted redirect. Forcing HTTPS: ", final_url)
+    
+  } else if (initial_req$status_code == 200) {
+    final_url <- target_url # No redirect occurred
+  } else {
+    stop("Initial request failed with status: ", initial_req$status_code)
+  }
+
+  # Download the actual file from the corrected URL
+  filename <- basename(final_url)
+  destfile <- file.path(download_dir, filename)
+  
+  message("Downloading to: ", destfile)
+  final_req <- httr::GET(
+    final_url, 
+    ua,
+    httr::write_disk(destfile, overwrite = TRUE)
+  )
+
+  if (httr::status_code(final_req) != 200) {
+    if (file.exists(destfile)) file.remove(destfile)
+    stop("Error downloading the file! Status code: ", httr::status_code(final_req))
+  }
+
+  return(destfile)
+}
+
+# Function constructs download URL for requested metalog data from DB,
+# If cache, checks if files already exist in datadir, and downloads if not.
+# Otherwise downloads files to datadir.
+.resolve_metalog_url <- function(collection, metadata, use_cache) {
+  cache_dir <- ".data_cache"
+  if (!dir.exists(cache_dir)) {
+    dir.create(cache_dir, recursive = TRUE, showWarnings = FALSE)
+  }
+
+  # Construct download URL's into target list
+  base_url <- "https://metalog.embl.de/static/download"
+  
+  profile <- collection
+  assay_url <- sprintf("%s/profiles/%s_metaphlan4_latest.tsv.gz", base_url, profile)
+
+  md_type <- metadata
+  md_url <- sprintf("%s/metadata/%s_%s_long_latest.tsv.gz", base_url, profile, md_type)
+
+  # Get files
+  assay_file <- .download_if_missing(
+    target_url = assay_url,
+    download_dir = cache_dir,
+    use_cache = use_cache
+  )
+
+  md_file <- .download_if_missing(
+    target_url = md_url,
+    download_dir = cache_dir,
+    use_cache = use_cache
+  )
+
+  return(list(
+    assay = assay_file,
+    md = md_file
+  ))
+}
+
+# Function loads assay profile as sparse matrix
+.load_assay <- function(path, sep = "\t") {
+  # Read and subset to SGB only
+  dt <- fread(path, sep = sep)
+  dt <- dt[startsWith(clade_name, "t__SGB"), ]
+
+  # Ensure expected names and types
+  setnames(dt, c("sample_alias", "clade_name", "rel_abund"))
+  dt[, rel_abund := as.numeric(rel_abund)]
+  dt <- dt[!is.na(rel_abund) & rel_abund != 0]
+
+  # Aggregate duplicates (taxon, sample) -> sum(rel_abund)
+  setkey(dt, clade_name, sample_alias)
+  dt <- dt[, .(rel_abund = sum(rel_abund)), by = .(clade_name, sample_alias)]
+  # Map taxa and samples
+  taxa <- sort(unique(dt$clade_name))
+  samples <- sort(unique(dt$sample_alias))
+  i <- match(dt$clade_name, taxa)
+  j <- match(dt$sample_alias, samples)
+  x <- dt$rel_abund
+
+  # Build sparse matrix (rows = taxa, cols = samples)
+  X <- sparseMatrix(
+    i = i, j = j, x = x,
+    dims = c(length(taxa), length(samples)),
+    dimnames = list(taxa, samples)
+  )
+  assay <- list(assay = X, taxa = taxa, samples = samples)
+  return(assay)
+}
+
+# Loads the metadata and filteres to samples found in assay
+.load_metadata <- function(meta_df, samples, sep = "\t") {
+  dt <- fread(meta_df, sep = sep, na.strings = c("", "NA"))
+
+  # Pivot to wide
+  wide <- dcast(
+    dt,
+    sample_alias ~ metadata_item,
+    value.var = "value",
+    fill = NA_character_
+  )
+
+  meta_df <- as.data.frame(wide)
+  rownames(meta_df) <- meta_df$sample_alias
+
+  # Output Dataframe subset to samples
+  meta_df <- meta_df[samples, ]
+  return(meta_df)
+}
+
+# Maps full lineage names levels
+.construct_taxmap <- function(database, taxa) {
+  taxmap <- fread(database, sep = "\t", header = TRUE)
+  taxmap <- taxmap[startsWith(clade_name, "t__SGB")]
+
+  taxmap <- taxmap %>%
+    distinct(clade_name, .keep_all = TRUE) %>%
+    filter(clade_name %in% taxa)
+
+  idx <- match(taxa, taxmap$clade_name)
+  taxmap <- taxmap[idx, ]
+
+  rownames(taxmap) <- taxmap$clade_name
+
+  taxmap <- taxmap %>%
+    filter(clade_name %in% taxa) %>%
+    tidyr::separate(
+      col = lineage,
+      into = c(
+        "Kingdom", "Phylum", "Class", "Order",
+        "Family", "Genus", "Species", "SGB"
+      ),
+      sep = "\\|",
+      fill = "right"
+    ) %>%
+    select(-NCBI_taxids, -clade_name) %>%
+    as.data.frame()
+
+  # Subset to taxa in present
+  taxmap <- taxmap[taxa, ]
+  return(taxmap)
+}
+
+# Function filters profile data down to provided samples
+.filter_datasets <- function(assay_list, samplelist) {
+  # Resolve the samplelist into a vector of target IDs
+  ext <- tolower(tools::file_ext(samplelist))
+
+  # Read file based on extension
+  if (ext %in% c("csv", "tsv")) {
+    sl_df <- data.table::fread(samplelist)
+  } else if (ext == "json") {
+    if (!requireNamespace("jsonlite", quietly = TRUE)) {
+      stop("The 'jsonlite' package is required to read JSON sample lists.")
+    }
+    sl_df <- as.data.frame(jsonlite::fromJSON(samplelist))
+  }
+  # Grab samples
+  target_samples <- sl_df[["sample_alias"]]
+
+  # Intersect requested samples with available samples
+  available_samples <- assay_list[["samples"]]
+  keep_samples <- intersect(target_samples, available_samples)
+
+  if (length(keep_samples) == 0) {
+    stop("Filtering Error: None of the provided samples were found in the dataset.")
+  }
+
+  # Subset the sparse matrix (columns = samples)
+  assay_list$assay <- assay_list$assay[, keep_samples, drop = FALSE]
+  assay_list$samples <- keep_samples
+
+  # Drop taxa that now have 0 abundance across all remaining samples
+  row_sums <- Matrix::rowSums(assay_list$assay)
+  keep_taxa <- names(row_sums[row_sums > 0])
+  assay_list$assay <- assay_list$assay[keep_taxa, , drop = FALSE]
+  assay_list$taxa <- keep_taxa
+
+  return(assay_list)
+}
+
+# -------------
+# Main function
+# -------------
+
+fetchMetalogTSE <- function(
+  collection, # One of "human", "animal", "ocean", "other_environment"
+  metadata = "core", # One of "core", "partially_harmonized", "all"
+  samplelist = NULL,
+  use_cache = TRUE
+) {
+  # Validate inputs
+  .validate_inputs(
+    collection = collection,
+    metadata = metadata,
+    samplelist = samplelist,
+    use_cache = use_cache
+  )
+
+  # Construct download URLs, download and cache
+  data_files <- .resolve_metalog_url(collection, metadata, use_cache)
+  # Lastest database file for tax mapping
+  mapping_db <- .download_if_missing(
+    "https://metalog.embl.de/static/download/profiles/metaphlan4_clades.tsv.gz",
+    use_cache = use_cache
+  )
+
+  # Injest data
+  assay_list <- .load_assay(data_files[["assay"]])
+
+  # Filtering
+  if (!is.null(samplelist)) {
+    message("Filtering datasets to include only the requested samples...")
+    assay_list <- .filter_datasets(assay_list, samplelist)
+  }
+  md_dt <- .load_metadata(data_files[["md"]], assay_list[["samples"]])
+
+  # Map SGB's to full lineage
+  tax <- .construct_taxmap(mapping_db, assay_list[["taxa"]])
+
+  tse <- TreeSummarizedExperiment(
+    assays  = SimpleList("relabundance" = assay_list[["assay"]]),
+    colData = DataFrame(md_dt),
+    rowData = DataFrame(tax)
+  )
+
+  # License injection
+  metadata(tse)$license <- "https://metalog.embl.de/ - Open Database License (ODbL) v1.0"
+
+  return(tse)
+}