diff --git a/Cargo.lock b/Cargo.lock
index a8e9d46..e64ccd2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -91,6 +91,12 @@ dependencies = [
  "rustversion",
 ]
 
+[[package]]
+name = "arrayref"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76a2e8124351fda1ef8aaaa3bbd7ebbcb486bbcd4225aca0aa0d84bb2db8fecb"
+
 [[package]]
 name = "arrayvec"
 version = "0.7.6"
@@ -135,6 +141,20 @@ dependencies = [
  "crunchy",
 ]
 
+[[package]]
+name = "blake3"
+version = "1.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2468ef7d57b3fb7e16b576e8377cdbde2320c60e1491e961d11da40fc4f02a2d"
+dependencies = [
+ "arrayref",
+ "arrayvec",
+ "cc",
+ "cfg-if",
+ "constant_time_eq",
+ "cpufeatures",
+]
+
 [[package]]
 name = "block-buffer"
 version = "0.11.0"
@@ -289,6 +309,12 @@ version = "0.10.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a6ef517f0926dd24a1582492c791b6a4818a4d94e789a334894aa15b0d12f55c"
 
+[[package]]
+name = "constant_time_eq"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d52eff69cd5e647efe296129160853a42795992097e8af39800e1060caeea9b"
+
 [[package]]
 name = "core-foundation-sys"
 version = "0.8.7"
@@ -448,7 +474,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
 dependencies = [
  "libc",
- "windows-sys 0.59.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -858,7 +884,7 @@ version = "0.50.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
 dependencies = [
- "windows-sys 0.59.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -968,6 +994,7 @@ dependencies = [
 name = "pile-dataset"
 version = "0.0.1"
 dependencies = [
+ "blake3",
  "chrono",
  "itertools",
  "pile-config",
@@ -979,6 +1006,7 @@ dependencies = [
  "tantivy",
  "thiserror",
  "toml",
+ "toml_edit",
  "tracing",
  "walkdir",
 ]
@@ -1196,7 +1224,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys",
- "windows-sys 0.59.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1569,10 +1597,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0136791f7c95b1f6dd99f9cc786b91bb81c3800b639b3478e561ddb7be95e5f1"
 dependencies = [
  "fastrand",
- "getrandom 0.3.4",
+ "getrandom 0.4.1",
  "once_cell",
  "rustix",
- "windows-sys 0.59.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1687,6 +1715,19 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "toml_edit"
+version = "0.25.4+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7193cbd0ce53dc966037f54351dbbcf0d5a642c7f0038c382ef9e677ce8c13f2"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "toml_parser",
+ "toml_writer",
+ "winnow",
+]
+
 [[package]]
 name = "toml_parser"
 version = "1.0.9+spec-1.1.0"
@@ -2026,7 +2067,7 @@ version = "0.1.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c2a7b1c03c876122aa43f3020e6c3c3ee5c05081c9a00739faf7503aeba10d22"
 dependencies = [
- "windows-sys 0.59.0",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -2255,6 +2296,9 @@ name = "winnow"
 version = "0.7.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5a5364e9d77fcdeeaa6062ced926ee3381faa2ee02d3eb83a5c27a8825540829"
+dependencies = [
+ "memchr",
+]
 
 [[package]]
 name = "wit-bindgen"
diff --git a/Cargo.toml b/Cargo.toml
index cd47aa3..f137f73 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -87,7 +87,9 @@ serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.149"
 base64 = "0.22.1"
 toml = "1.0.3"
+toml_edit = "0.25.4"
 sha2 = "0.11.0-rc.5"
+blake3 = "1.8.3"
 
 # Misc helpers
 thiserror = "2.0.18"
diff --git a/crates/pile-dataset/Cargo.toml b/crates/pile-dataset/Cargo.toml
index d60c1c9..b65142a 100644
--- a/crates/pile-dataset/Cargo.toml
+++ b/crates/pile-dataset/Cargo.toml
@@ -22,3 +22,5 @@ toml = { workspace = true }
 thiserror = { workspace = true }
 rayon = { workspace = true }
 smartstring = { workspace = true }
+blake3 = { workspace = true }
+toml_edit = { workspace = true }
diff --git a/crates/pile-dataset/src/dataset.rs b/crates/pile-dataset/src/dataset.rs
index 27f9d2c..c20823a 100644
--- a/crates/pile-dataset/src/dataset.rs
+++ b/crates/pile-dataset/src/dataset.rs
@@ -21,7 +21,7 @@ use thiserror::Error;
 use tracing::{debug, info, trace, warn};
 
 use crate::{
-	DataSource, Item,
+	DataSource, FileItem,
 	index::{DbFtsIndex, FtsLookupResult},
 	path_ts_earliest,
 	source::DirDataSource,
@@ -96,11 +96,7 @@ impl Dataset {
 	// MARK: get
 	//
 
-	pub fn get(
-		&self,
-		source: &Label,
-		key: &PathBuf,
-	) -> Option<Box<dyn Item<Key = PathBuf> + 'static>> {
+	pub fn get(&self, source: &Label, key: &PathBuf) -> Option<FileItem> {
 		let s = self.config.dataset.source.get(source)?;
 		let s = match s {
 			Source::Filesystem { path, sidecars } => {
@@ -115,7 +111,7 @@ impl Dataset {
 	// MARK: fts
 	//
 
-	/// Refresh this dataset's fts index
+	/// Refresh this dataset's fts index.
 	pub fn fts_refresh(
 		&self,
 		threads: usize,
@@ -163,7 +159,7 @@ impl Dataset {
 				.install(|| {
 					batch
 						.into_par_iter()
-						.filter_map(|(key, item)| match db_index.entry_to_document(&*item) {
+						.filter_map(|(key, item)| match db_index.entry_to_document(&item) {
 							Ok(Some(doc)) => Some((key, doc)),
 							Ok(None) => {
 								warn!("Skipping {key:?}, document is empty");
@@ -306,7 +302,7 @@ fn start_read_task(
 	batch_size: usize,
 ) -> (
 	JoinHandle<()>,
-	Receiver<Result<Vec<(PathBuf, Box<dyn Item<Key = PathBuf>>)>, DatasetError>>,
+	Receiver<Result<Vec<(PathBuf, FileItem)>, DatasetError>>,
 ) {
 	let config = config.clone();
 	let (read_tx, read_rx) = std::sync::mpsc::sync_channel(2);
diff --git a/crates/pile-dataset/src/extract/sidecar.rs b/crates/pile-dataset/src/extract/sidecar.rs
index b282877..77f09ce 100644
--- a/crates/pile-dataset/src/extract/sidecar.rs
+++ b/crates/pile-dataset/src/extract/sidecar.rs
@@ -39,9 +39,11 @@ impl<'a> SidecarExtractor<'a> {
 			return Ok(self.output.get_or_init(HashMap::new));
 		}
 
-		let sidecar = std::fs::read_to_string(&sidecar_file)?;
-		let sidecar: toml::Value = toml::from_str(&sidecar)
-			.map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;
+		let sidecar = std::fs::read(&sidecar_file)?;
+		let sidecar: toml::Value = match toml::from_slice(&sidecar) {
+			Ok(x) => x,
+			Err(_) => return Ok(self.output.get_or_init(HashMap::new)),
+		};
 
 		let output: HashMap<Label, PileValue<'_, FileItem>> = match sidecar {
 			toml::Value::Table(t) => t
diff --git a/crates/pile-dataset/src/index/index_fts.rs b/crates/pile-dataset/src/index/index_fts.rs
index 95aa23d..8937fe3 100644
--- a/crates/pile-dataset/src/index/index_fts.rs
+++ b/crates/pile-dataset/src/index/index_fts.rs
@@ -63,9 +63,9 @@ impl DbFtsIndex {
 	//
 
 	/// Turn an entry into a tantivy document
-	pub fn entry_to_document<K: Key>(
+	pub fn entry_to_document<K: Key, I: Item<Key = K>>(
 		&self,
-		item: &dyn Item<Key = K>,
+		item: &I,
 	) -> Result<Option<TantivyDocument>, TantivyError> {
 		let mut doc = TantivyDocument::default();
 
diff --git a/crates/pile-dataset/src/item.rs b/crates/pile-dataset/src/item.rs
index a274547..1513679 100644
--- a/crates/pile-dataset/src/item.rs
+++ b/crates/pile-dataset/src/item.rs
@@ -1,5 +1,10 @@
 use pile_config::Label;
-use std::{fmt::Debug, path::PathBuf};
+use std::{fmt::Debug, path::PathBuf, rc::Rc};
+
+use crate::{
+	PileValue,
+	extract::{Extractor, SidecarExtractor},
+};
 
 //
 // MARK: key
@@ -28,12 +33,27 @@ impl Key for PathBuf {
 //
 
 /// A pointer to raw data
-pub trait Item: Debug + Send + Sync + 'static {
+pub trait Item: Debug + Send + Sync + 'static + Sized {
 	type Key: Key;
 
 	fn source_name(&self) -> &str;
 	fn key(&self) -> &Self::Key;
 
+	/// Get this item's sidecar metadata
+	fn sidecar(&self) -> Result<Option<Rc<dyn Extractor<Self> + '_>>, std::io::Error>;
+
+	/// Set this file's sidecar metadata,
+	/// overwriting any existing file.
+	fn write_sidecar(
+		&self,
+		path: Vec<Label>,
+		value: PileValue<'_, Self>,
+	) -> Result<(), std::io::Error>;
+
+	fn hash(&self) -> Result<blake3::Hash, std::io::Error>;
+
+	/// Item conversion, downcast to specific type.
+	/// Returns `None` if this is not a [FileItem]
 	fn as_file(&self) -> Option<&FileItem>;
 }
 
@@ -62,4 +82,97 @@ impl Item for FileItem {
 	fn as_file(&self) -> Option<&FileItem> {
 		Some(self)
 	}
+
+	fn hash(&self) -> Result<blake3::Hash, std::io::Error> {
+		let mut hasher = blake3::Hasher::new();
+		let mut file = std::fs::File::open(&self.path)?;
+		std::io::copy(&mut file, &mut hasher)?;
+		return Ok(hasher.finalize());
+	}
+
+	fn sidecar(&self) -> Result<Option<Rc<dyn Extractor<Self> + '_>>, std::io::Error> {
+		if !self.sidecar {
+			return Ok(None);
+		}
+
+		// TODO: use a generic tomlextractor instead?
+		// you'll need a fake _ref_ to the toml file, though.
+		return Ok(Some(Rc::new(SidecarExtractor::new(self))));
+	}
+
+	fn write_sidecar(
+		&self,
+		path: Vec<Label>,
+		value: PileValue<'_, Self>,
+	) -> Result<(), std::io::Error> {
+		if !self.sidecar {
+			return Ok(());
+		}
+
+		let sidecar_path = self.path.with_extension("toml");
+
+		let mut doc: toml_edit::DocumentMut = if sidecar_path.is_file() {
+			let content = std::fs::read_to_string(&sidecar_path)?;
+			content.parse().unwrap_or_default()
+		} else {
+			toml_edit::DocumentMut::new()
+		};
+
+		fn to_edit_item(v: toml::Value) -> toml_edit::Item {
+			match v {
+				toml::Value::String(s) => toml_edit::value(s),
+				toml::Value::Integer(i) => toml_edit::value(i),
+				toml::Value::Float(f) => toml_edit::value(f),
+				toml::Value::Boolean(b) => toml_edit::value(b),
+				toml::Value::Datetime(d) => toml_edit::value(d.to_string()),
+				toml::Value::Array(arr) => {
+					let mut array = toml_edit::Array::new();
+					for item in arr {
+						if let toml_edit::Item::Value(v) = to_edit_item(item) {
+							array.push_formatted(v);
+						}
+					}
+					toml_edit::Item::Value(toml_edit::Value::Array(array))
+				}
+				toml::Value::Table(t) => {
+					let mut table = toml_edit::Table::new();
+					for (k, v) in t {
+						table.insert(&k, to_edit_item(v));
+					}
+					toml_edit::Item::Table(table)
+				}
+			}
+		}
+
+		let json_value = value.to_json()?;
+		let toml_value: toml::Value = serde_json::from_value(json_value)
+			.map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;
+		let item = to_edit_item(toml_value);
+
+		let Some((path_last, path_init)) = path.split_last() else {
+			return Ok(());
+		};
+
+		let mut table = doc.as_table_mut();
+		for label in path_init {
+			let key = label.as_str();
+			if !table.contains_key(key) {
+				table.insert(key, toml_edit::Item::Table(toml_edit::Table::new()));
+			}
+			table = table
+				.get_mut(key)
+				.and_then(|item| item.as_table_mut())
+				.ok_or_else(|| {
+					std::io::Error::new(
+						std::io::ErrorKind::InvalidData,
+						"path element is not a table",
+					)
+				})?;
+		}
+		table.insert(path_last.as_str(), item);
+
+		std::fs::write(&sidecar_path, doc.to_string())?;
+
+		Ok(())
+	}
 }
diff --git a/crates/pile-dataset/src/source/dir.rs b/crates/pile-dataset/src/source/dir.rs
index 15b582f..954dfa0 100644
--- a/crates/pile-dataset/src/source/dir.rs
+++ b/crates/pile-dataset/src/source/dir.rs
@@ -4,7 +4,7 @@ use pile_config::Label;
 use std::path::PathBuf;
 use walkdir::WalkDir;
 
-use crate::{DataSource, Item, item::FileItem, path_ts_latest};
+use crate::{DataSource, item::FileItem, path_ts_latest};
 
 #[derive(Debug)]
 pub struct DirDataSource {
@@ -26,26 +26,27 @@ impl DirDataSource {
 
 impl DataSource for DirDataSource {
 	type Key = PathBuf;
+	type Item = FileItem;
 	type Error = std::io::Error;
 
-	fn get(
-		&self,
-		key: &Self::Key,
-	) -> Result<Option<Box<dyn Item<Key = Self::Key> + 'static>>, Self::Error> {
+	fn get(&self, key: &Self::Key) -> Result<Option<Self::Item>, Self::Error> {
 		if !key.is_file() {
 			return Ok(None);
 		}
 
-		return Ok(Some(Box::new(FileItem {
+		// Ignore toml files if sidecars are enabled
+		if self.sidecars && key.extension().and_then(|x| x.to_str()) == Some("toml") {
+			return Ok(None);
+		}
+
+		return Ok(Some(FileItem {
 			source_name: self.name.clone(),
 			path: key.to_owned(),
 			sidecar: self.sidecars,
-		})));
+		}));
 	}
 
-	fn iter(
-		&self,
-	) -> impl Iterator<Item = Result<(Self::Key, Box<dyn Item<Key = Self::Key>>), Self::Error>> {
+	fn iter(&self) -> impl Iterator<Item = Result<(Self::Key, Self::Item), Self::Error>> {
 		return self
 			.dirs
 			.iter()
@@ -62,16 +63,18 @@ impl DataSource for DirDataSource {
 				Ok((_, entry)) => {
 					let path = entry.into_path();
 
-					let item: Box<dyn Item<Key = Self::Key>> =
-						match path.extension().and_then(|x| x.to_str()) {
-							None => return None,
-							Some("flac") => Box::new(FileItem {
-								source_name: self.name.clone(),
-								path: path.clone(),
-								sidecar: self.sidecars,
-							}),
-							Some(_) => return None,
-						};
+					let item = match path.extension().and_then(|x| x.to_str()) {
+						None => return None,
+
+						// Ignore toml if sidecars are enabled
+						Some("toml") if self.sidecars => return None,
+
+						Some(_) => FileItem {
+							source_name: self.name.clone(),
+							path: path.clone(),
+							sidecar: self.sidecars,
+						},
+					};
 
 					Some(Ok((path, item)))
 				}
diff --git a/crates/pile-dataset/src/traits.rs b/crates/pile-dataset/src/traits.rs
index 4359e52..bd9f04a 100644
--- a/crates/pile-dataset/src/traits.rs
+++ b/crates/pile-dataset/src/traits.rs
@@ -8,19 +8,15 @@ pub trait DataSource {
 	/// The type used to retrieve items from this source
 	/// (e.g, a PathBuf or a primary key)
 	type Key: Key;
+	type Item: Item<Key = Self::Key>;
 
 	type Error: Error + Sync + Send;
 
 	/// Get an item from this datasource
-	fn get(
-		&self,
-		key: &Self::Key,
-	) -> Result<Option<Box<dyn Item<Key = Self::Key> + 'static>>, Self::Error>;
+	fn get(&self, key: &Self::Key) -> Result<Option<Self::Item>, Self::Error>;
 
 	/// Iterate over all items in this source in an arbitrary order
-	fn iter(
-		&self,
-	) -> impl Iterator<Item = Result<(Self::Key, Box<dyn Item<Key = Self::Key> + 'static>), Self::Error>>;
+	fn iter(&self) -> impl Iterator<Item = Result<(Self::Key, Self::Item), Self::Error>>;
 
 	/// Return the time of the latest change to the data in this source
 	fn latest_change(&self) -> Result<Option<DateTime<Utc>>, Self::Error>;
diff --git a/crates/pile/src/command/annotate.rs b/crates/pile/src/command/annotate.rs
new file mode 100644
index 0000000..60d3734
--- /dev/null
+++ b/crates/pile/src/command/annotate.rs
@@ -0,0 +1,96 @@
+use anyhow::{Context, Result};
+use clap::Args;
+use pile_config::{Label, Source};
+use pile_dataset::index::DbFtsIndex;
+use pile_dataset::source::DirDataSource;
+use pile_dataset::{DataSource, Dataset, FileItem, Item, PileValue, extract::MetaExtractor};
+use pile_toolbox::cancelabletask::{CancelFlag, CancelableTaskError};
+use std::{path::PathBuf, rc::Rc};
+use tracing::{info, warn};
+
+use crate::{CliCmd, GlobalContext};
+
+#[derive(Debug, Args)]
+pub struct AnnotateCommand {
+	/// The schema field to read (must be defined in pile.toml)
+	field: String,
+
+	/// Sidecar path to write to (e.g. meta.title)
+	dest: String,
+
+	/// Path to dataset config
+	#[arg(long, short = 'c', default_value = "./pile.toml")]
+	config: PathBuf,
+}
+
+impl AnnotateCommand {
+	fn parse_dest(dest: &str) -> Result<Vec<Label>> {
+		dest.split('.')
+			.map(|s| {
+				Label::new(s).ok_or_else(|| anyhow::anyhow!("invalid label {s:?} in dest path"))
+			})
+			.collect()
+	}
+}
+
+impl CliCmd for AnnotateCommand {
+	async fn run(
+		self,
+		_ctx: GlobalContext,
+		_flag: CancelFlag,
+	) -> Result<i32, CancelableTaskError<anyhow::Error>> {
+		let field = Label::new(&self.field)
+			.ok_or_else(|| anyhow::anyhow!("invalid field name {:?}", self.field))?;
+		let dest_path = Self::parse_dest(&self.dest)?;
+
+		let ds = Dataset::open(&self.config)
+			.with_context(|| format!("while opening dataset for {}", self.config.display()))?;
+
+		if !ds.config.schema.contains_key(&field) {
+			return Err(anyhow::anyhow!("field {:?} is not defined in schema", self.field).into());
+		}
+
+		let index = DbFtsIndex::new(&ds.path_workdir, &ds.config);
+		let mut count = 0u64;
+
+		for (name, source) in &ds.config.dataset.source {
+			match source {
+				Source::Filesystem { path, sidecars } => {
+					if !sidecars {
+						warn!("Source {name} does not have sidecars enabled, skipping");
+						continue;
+					}
+
+					let source = DirDataSource::new(name, path.clone().to_vec(), *sidecars);
+
+					for res in source.iter() {
+						let (_key, item) =
+							res.with_context(|| format!("while reading source {name}"))?;
+
+						let meta = MetaExtractor::new(&item);
+						let extractor = PileValue::<FileItem>::Extractor(Rc::new(meta));
+
+						let Some(value) =
+							index.get_field(&extractor, &field).with_context(|| {
+								format!("while extracting field from {}", item.path.display())
+							})?
+						else {
+							continue;
+						};
+
+						item.write_sidecar(dest_path.clone(), PileValue::String(value.into()))
+							.with_context(|| {
+								format!("while writing sidecar for {}", item.path.display())
+							})?;
+
+						count += 1;
+					}
+				}
+			}
+		}
+
+		info!("Annotated {count} items");
+
+		return Ok(0);
+	}
+}
diff --git a/crates/pile/src/command/mod.rs b/crates/pile/src/command/mod.rs
index 631b379..d3a09a1 100644
--- a/crates/pile/src/command/mod.rs
+++ b/crates/pile/src/command/mod.rs
@@ -2,6 +2,7 @@ use anyhow::Result;
 use clap::Subcommand;
 use pile_toolbox::cancelabletask::{CancelFlag, CancelableTask, CancelableTaskError};
 
+mod annotate;
 mod check;
 mod index;
 mod init;
@@ -12,6 +13,12 @@ use crate::GlobalContext;
 
 #[derive(Debug, Subcommand)]
 pub enum SubCommand {
+	/// Annotate all items with a field, writing it to a sidecar path
+	Annotate {
+		#[command(flatten)]
+		cmd: annotate::AnnotateCommand,
+	},
+
 	/// Create an empty dataset
 	Init {
 		#[command(flatten)]
@@ -46,6 +53,7 @@ pub enum SubCommand {
 impl CliCmdDispatch for SubCommand {
 	fn start(self, ctx: GlobalContext) -> Result<CancelableTask<Result<i32>>> {
 		match self {
+			Self::Annotate { cmd } => cmd.start(ctx),
 			Self::Init { cmd } => cmd.start(ctx),
 			Self::Check { cmd } => cmd.start(ctx),
 			Self::Index { cmd } => cmd.start(ctx),