diff --git a/src/compose/composer.ts b/src/compose/composer.ts
index 598ba78b..3fe9248a 100644
--- a/src/compose/composer.ts
+++ b/src/compose/composer.ts
@@ -133,7 +133,12 @@ export class Composer<
    *
    * Mostly useful at the end of input for an empty stream.
    */
-  streamInfo() {
+  streamInfo(): {
+    comment: string
+    directives: Directives
+    errors: YAMLParseError[]
+    warnings: YAMLWarning[]
+  } {
     return {
       comment: parsePrelude(this.prelude).comment,
       directives: this.directives,
@@ -148,13 +153,19 @@ export class Composer<
    * @param forceDoc - If the stream contains no document, still emit a final document including any comments and directives that would be applied to a subsequent document.
    * @param endOffset - Should be set if `forceDoc` is also set, to set the document range end and to indicate errors correctly.
    */
-  *compose(tokens: Iterable<Token>, forceDoc = false, endOffset = -1) {
+  *compose(
+    tokens: Iterable<Token>,
+    forceDoc = false,
+    endOffset = -1
+  ): Generator<Document.Parsed<Contents, Strict>, void, unknown> {
     for (const token of tokens) yield* this.next(token)
     yield* this.end(forceDoc, endOffset)
   }
 
   /** Advance the composer by one CST token. */
-  *next(token: Token) {
+  *next(
+    token: Token
+  ): Generator<Document.Parsed<Contents, Strict>, void, unknown> {
     if (process.env.LOG_STREAM) console.dir(token, { depth: null })
     switch (token.type) {
       case 'directive':
@@ -245,7 +256,10 @@ export class Composer<
    * @param forceDoc - If the stream contains no document, still emit a final document including any comments and directives that would be applied to a subsequent document.
    * @param endOffset - Should be set if `forceDoc` is also set, to set the document range end and to indicate errors correctly.
    */
-  *end(forceDoc = false, endOffset = -1) {
+  *end(
+    forceDoc = false,
+    endOffset = -1
+  ): Generator<Document.Parsed<Contents, Strict>, void, unknown> {
     if (this.doc) {
       this.decorate(this.doc, true)
       yield this.doc
diff --git a/src/doc/Document.ts b/src/doc/Document.ts
index 14456486..782f87d5 100644
--- a/src/doc/Document.ts
+++ b/src/doc/Document.ts
@@ -265,7 +265,7 @@ export class Document<
     key: unknown,
     value: unknown,
     options: CreateNodeOptions = {}
-  ) {
+  ): Pair<K, V> {
     const k = this.createNode(key, null, options) as K
     const v = this.createNode(value, null, options) as V
     return new Pair(k, v)
diff --git a/src/doc/directives.ts b/src/doc/directives.ts
index 37f1ce0b..55227a86 100644
--- a/src/doc/directives.ts
+++ b/src/doc/directives.ts
@@ -53,7 +53,7 @@ export class Directives {
    * During parsing, get a Directives instance for the current document and
    * update the stream state according to the current version's spec.
    */
-  atDocument() {
+  atDocument(): Directives {
     const res = new Directives(this.yaml, this.tags)
     switch (this.yaml.version) {
       case '1.1':
@@ -78,7 +78,7 @@ export class Directives {
   add(
     line: string,
     onError: (offset: number, message: string, warning?: boolean) => void
-  ) {
+  ): boolean {
     if (this.atNextDocument) {
       this.yaml = { explicit: Directives.defaultYaml.explicit, version: '1.1' }
       this.tags = Object.assign({}, Directives.defaultTags)
@@ -124,7 +124,7 @@ export class Directives {
    * @returns Resolved tag, which may also be the non-specific tag `'!'` or a
    *   `'!local'` tag, or `null` if unresolvable.
    */
-  tagName(source: string, onError: (message: string) => void) {
+  tagName(source: string, onError: (message: string) => void): string | null {
     if (source === '!') return '!' // non-specific tag
 
     if (source[0] !== '!') {
@@ -164,7 +164,7 @@ export class Directives {
    * Given a fully resolved tag, returns its printable string form,
    * taking into account current tag prefixes and defaults.
    */
-  tagString(tag: string) {
+  tagString(tag: string): string {
     for (const [handle, prefix] of Object.entries(this.tags)) {
       if (tag.startsWith(prefix))
         return handle + escapeTagName(tag.substring(prefix.length))
@@ -172,7 +172,7 @@ export class Directives {
     return tag[0] === '!' ? tag : `!<${tag}>`
   }
 
-  toString(doc?: Document) {
+  toString(doc?: Document): string {
     const lines = this.yaml.explicit
       ? [`%YAML ${this.yaml.version || '1.2'}`]
       : []
diff --git a/src/nodes/Alias.ts b/src/nodes/Alias.ts
index 8461c3df..bcc1d57e 100644
--- a/src/nodes/Alias.ts
+++ b/src/nodes/Alias.ts
@@ -49,7 +49,7 @@ export class Alias extends NodeBase {
     return found
   }
 
-  toJSON(_arg?: unknown, ctx?: ToJSContext) {
+  toJSON(_arg?: unknown, ctx?: ToJSContext): unknown {
     if (!ctx) return { source: this.source }
     const { anchors, doc, maxAliasCount } = ctx
     const source = this.resolve(doc)
@@ -85,7 +85,7 @@ export class Alias extends NodeBase {
     ctx?: StringifyContext,
     _onComment?: () => void,
     _onChompKeep?: () => void
-  ) {
+  ): string {
     const src = `*${this.source}`
     if (ctx) {
       anchorIsValid(this.source)
diff --git a/src/nodes/Collection.ts b/src/nodes/Collection.ts
index 9e336b91..171ff2cf 100644
--- a/src/nodes/Collection.ts
+++ b/src/nodes/Collection.ts
@@ -163,7 +163,7 @@ export abstract class Collection extends NodeBase {
     else return isCollection(node) ? node.getIn(rest, keepScalar) : undefined
   }
 
-  hasAllNullValues(allowScalar?: boolean) {
+  hasAllNullValues(allowScalar?: boolean): boolean {
     return this.items.every(node => {
       if (!isPair(node)) return false
       const n = node.value
diff --git a/src/nodes/Pair.ts b/src/nodes/Pair.ts
index e3f369f2..f41a8791 100644
--- a/src/nodes/Pair.ts
+++ b/src/nodes/Pair.ts
@@ -6,13 +6,14 @@ import type { StringifyContext } from '../stringify/stringify.ts'
 import { stringifyPair } from '../stringify/stringifyPair.ts'
 import { addPairToJSMap } from './addPairToJSMap.ts'
 import { isNode, NODE_TYPE, PAIR } from './identity.ts'
+import type { Node } from './Node.ts'
 import type { ToJSContext } from './toJS.ts'
 
 export function createPair(
   key: unknown,
   value: unknown,
   ctx: CreateNodeContext
-) {
+): Pair<Node, Node> {
   const k = createNode(key, undefined, ctx)
   const v = createNode(value, undefined, ctx)
   return new Pair(k, v)
diff --git a/src/nodes/Scalar.ts b/src/nodes/Scalar.ts
index b9d92cd6..982a65cd 100644
--- a/src/nodes/Scalar.ts
+++ b/src/nodes/Scalar.ts
@@ -61,7 +61,7 @@ export class Scalar<T = unknown> extends NodeBase {
     return ctx?.keep ? this.value : toJS(this.value, arg, ctx)
   }
 
-  toString() {
+  toString(): string {
     return String(this.value)
   }
 }
diff --git a/src/nodes/YAMLMap.ts b/src/nodes/YAMLMap.ts
index 23df326f..6169e14f 100644
--- a/src/nodes/YAMLMap.ts
+++ b/src/nodes/YAMLMap.ts
@@ -20,7 +20,7 @@ export type MapLike =
 export function findPair<K = unknown, V = unknown>(
   items: Iterable<Pair<K, V>>,
   key: unknown
-) {
+): Pair<K, V> | undefined {
   const k = isScalar(key) ? key.value : key
   for (const it of items) {
     if (isPair(it)) {
@@ -57,7 +57,7 @@ export class YAMLMap<K = unknown, V = unknown> extends Collection {
    * A generic collection parsing method that can be extended
    * to other node classes that inherit from YAMLMap
    */
-  static from(schema: Schema, obj: unknown, ctx: CreateNodeContext) {
+  static from(schema: Schema, obj: unknown, ctx: CreateNodeContext): YAMLMap {
     const { keepUndefined, replacer } = ctx
     const map = new this(schema)
     const add = (key: unknown, value: unknown) => {
diff --git a/src/nodes/YAMLSeq.ts b/src/nodes/YAMLSeq.ts
index 39e78dfb..c3f96e99 100644
--- a/src/nodes/YAMLSeq.ts
+++ b/src/nodes/YAMLSeq.ts
@@ -98,7 +98,7 @@ export class YAMLSeq<T = unknown> extends Collection {
     else this.items[idx] = value
   }
 
-  toJSON(_?: unknown, ctx?: ToJSContext) {
+  toJSON(_?: unknown, ctx?: ToJSContext): unknown[] {
     const seq: unknown[] = []
     if (ctx?.onCreate) ctx.onCreate(seq)
     let i = 0
@@ -121,7 +121,7 @@ export class YAMLSeq<T = unknown> extends Collection {
     })
   }
 
-  static from(schema: Schema, obj: unknown, ctx: CreateNodeContext) {
+  static from(schema: Schema, obj: unknown, ctx: CreateNodeContext): YAMLSeq {
     const { replacer } = ctx
     const seq = new this(schema)
     if (obj && Symbol.iterator in Object(obj)) {
diff --git a/src/nodes/addPairToJSMap.ts b/src/nodes/addPairToJSMap.ts
index 08bb0608..54806eba 100644
--- a/src/nodes/addPairToJSMap.ts
+++ b/src/nodes/addPairToJSMap.ts
@@ -11,7 +11,7 @@ export function addPairToJSMap(
   ctx: ToJSContext | undefined,
   map: MapLike,
   { key, value }: Pair
-) {
+): MapLike {
   if (isNode(key) && key.addToJSMap) key.addToJSMap(ctx, map, value)
   // TODO: Should drop this special case for bare << handling
   else if (isMergeKey(ctx, key)) addMergeToJSMap(ctx, map, value)
diff --git a/src/parse/cst-stringify.ts b/src/parse/cst-stringify.ts
index e428c2c7..7ccb5510 100644
--- a/src/parse/cst-stringify.ts
+++ b/src/parse/cst-stringify.ts
@@ -6,10 +6,10 @@ import type { CollectionItem, Token } from './cst.ts'
  * Fair warning: This applies no validation whatsoever, and
  * simply concatenates the sources in their logical order.
  */
-export const stringify = (cst: Token | CollectionItem) =>
+export const stringify = (cst: Token | CollectionItem): string =>
   'type' in cst ? stringifyToken(cst) : stringifyItem(cst)
 
-function stringifyToken(token: Token) {
+function stringifyToken(token: Token): string {
   switch (token.type) {
     case 'block-scalar': {
       let res = ''
@@ -42,7 +42,7 @@ function stringifyToken(token: Token) {
   }
 }
 
-function stringifyItem({ start, key, sep, value }: CollectionItem) {
+function stringifyItem({ start, key, sep, value }: CollectionItem): string {
   let res = ''
   for (const st of start) res += st.source
   if (key) res += stringifyToken(key)
diff --git a/src/parse/cst-visit.ts b/src/parse/cst-visit.ts
index 01b9aa9d..3961906c 100644
--- a/src/parse/cst-visit.ts
+++ b/src/parse/cst-visit.ts
@@ -1,4 +1,10 @@
-import type { CollectionItem, Document } from './cst.ts'
+import type {
+  BlockMap,
+  BlockSequence,
+  CollectionItem,
+  Document,
+  FlowCollection
+} from './cst.ts'
 
 const BREAK = Symbol('break visit')
 const SKIP = Symbol('skip children')
@@ -39,7 +45,7 @@ export type Visitor = (
  *     visitor is called on item entry, next visitors are called after handling
  *     a non-empty `key` and when exiting the item.
  */
-export function visit(cst: Document | CollectionItem, visitor: Visitor) {
+export function visit(cst: Document | CollectionItem, visitor: Visitor): void {
   if ('type' in cst && cst.type === 'document')
     cst = { start: cst.start, value: cst.value }
   _visit(Object.freeze([]), cst, visitor)
@@ -59,7 +65,10 @@ visit.SKIP = SKIP as symbol
 visit.REMOVE = REMOVE as symbol
 
 /** Find the item at `path` from `cst` as the root */
-visit.itemAtPath = (cst: Document | CollectionItem, path: VisitPath) => {
+visit.itemAtPath = (
+  cst: Document | CollectionItem,
+  path: VisitPath
+): CollectionItem | undefined => {
   let item: CollectionItem = cst
   for (const [field, index] of path) {
     const tok = item?.[field]
@@ -75,7 +84,10 @@ visit.itemAtPath = (cst: Document | CollectionItem, path: VisitPath) => {
  *
  * Throws an error if the collection is not found, which should never happen if the item itself exists.
  */
-visit.parentCollection = (cst: Document | CollectionItem, path: VisitPath) => {
+visit.parentCollection = (
+  cst: Document | CollectionItem,
+  path: VisitPath
+): BlockMap | BlockSequence | FlowCollection => {
   const parent = visit.itemAtPath(cst, path.slice(0, -1))
   const field = path[path.length - 1][0]
   const coll = parent?.[field]
diff --git a/src/parse/cst.ts b/src/parse/cst.ts
index c73cdcc3..a945ea03 100644
--- a/src/parse/cst.ts
+++ b/src/parse/cst.ts
@@ -174,7 +174,7 @@ export const isScalar = (
 
 /* istanbul ignore next */
 /** Get a printable representation of a lexer token */
-export function prettyToken(token: string) {
+export function prettyToken(token: string): string {
   switch (token) {
     case BOM:
       return '<BOM>'
diff --git a/src/parse/lexer.ts b/src/parse/lexer.ts
index ebe7f137..c8ab6437 100644
--- a/src/parse/lexer.ts
+++ b/src/parse/lexer.ts
@@ -171,7 +171,7 @@ export class Lexer {
    *
    * @returns A generator of lexical tokens
    */
-  *lex(source: string, incomplete = false) {
+  *lex(source: string, incomplete = false): Generator<string, void> {
     if (source) {
       if (typeof source !== 'string') throw TypeError('source is not a string')
       this.buffer = this.buffer ? this.buffer + source : source
diff --git a/src/parse/line-counter.ts b/src/parse/line-counter.ts
index f5ba111e..633eaa11 100644
--- a/src/parse/line-counter.ts
+++ b/src/parse/line-counter.ts
@@ -10,14 +10,14 @@ export class LineCounter {
    * Should be called in ascending order. Otherwise, call
    * `lineCounter.lineStarts.sort()` before calling `linePos()`.
    */
-  addNewLine = (offset: number) => this.lineStarts.push(offset)
+  addNewLine = (offset: number): number => this.lineStarts.push(offset)
 
   /**
    * Performs a binary search and returns the 1-indexed { line, col }
    * position of `offset`. If `line === 0`, `addNewLine` has never been
    * called or `offset` is before the first known newline.
    */
-  linePos = (offset: number) => {
+  linePos = (offset: number): { line: number; col: number } => {
     let low = 0
     let high = this.lineStarts.length
     while (low < high) {
diff --git a/src/parse/parser.ts b/src/parse/parser.ts
index 2828e564..2d19e824 100644
--- a/src/parse/parser.ts
+++ b/src/parse/parser.ts
@@ -176,7 +176,7 @@ export class Parser {
    *
    * @returns A generator of tokens representing each directive, document, and other structure.
    */
-  *parse(source: string, incomplete = false) {
+  *parse(source: string, incomplete = false): Generator<Token, void> {
     if (this.onNewLine && this.offset === 0) this.onNewLine(0)
     for (const lexeme of this.lexer.lex(source, incomplete))
       yield* this.next(lexeme)
@@ -186,7 +186,7 @@ export class Parser {
   /**
    * Advance the parser by the `source` of one lexical token.
    */
-  *next(source: string) {
+  *next(source: string): Generator<Token, void> {
     this.source = source
     if (env.LOG_TOKENS) console.log('|', prettyToken(source))
 
@@ -237,7 +237,7 @@ export class Parser {
   private lexer = new Lexer();
 
   /** Call at end of input to push out any remaining constructions */
-  *end() {
+  *end(): Generator<Token, void> {
     while (this.stack.length > 0) yield* this.pop()
   }
 
diff --git a/src/schema/yaml-1.1/omap.ts b/src/schema/yaml-1.1/omap.ts
index f3baa1a8..cd14c3e4 100644
--- a/src/schema/yaml-1.1/omap.ts
+++ b/src/schema/yaml-1.1/omap.ts
@@ -16,17 +16,17 @@ export class YAMLOMap extends YAMLSeq {
     this.tag = YAMLOMap.tag
   }
 
-  add = YAMLMap.prototype.add.bind(this)
-  delete = YAMLMap.prototype.delete.bind(this)
-  get = YAMLMap.prototype.get.bind(this)
-  has = YAMLMap.prototype.has.bind(this)
-  set = YAMLMap.prototype.set.bind(this)
+  add: typeof YAMLMap.prototype.add = YAMLMap.prototype.add.bind(this)
+  delete: typeof YAMLMap.prototype.delete = YAMLMap.prototype.delete.bind(this)
+  get: typeof YAMLMap.prototype.get = YAMLMap.prototype.get.bind(this)
+  has: typeof YAMLMap.prototype.has = YAMLMap.prototype.has.bind(this)
+  set: typeof YAMLMap.prototype.set = YAMLMap.prototype.set.bind(this)
 
   /**
    * If `ctx` is given, the return type is actually `Map<unknown, unknown>`,
    * but TypeScript won't allow widening the signature of a child method.
    */
-  toJSON(_?: unknown, ctx?: ToJSContext) {
+  toJSON(_?: unknown, ctx?: ToJSContext): unknown[] {
     if (!ctx) return super.toJSON(_)
     const map = new Map()
     if (ctx?.onCreate) ctx.onCreate(map)
@@ -45,7 +45,11 @@ export class YAMLOMap extends YAMLSeq {
     return map as unknown as unknown[]
   }
 
-  static from(schema: Schema, iterable: unknown, ctx: CreateNodeContext) {
+  static from(
+    schema: Schema,
+    iterable: unknown,
+    ctx: CreateNodeContext
+  ): YAMLOMap {
     const pairs = createPairs(schema, iterable, ctx)
     const omap = new this()
     omap.items = pairs.items
diff --git a/src/schema/yaml-1.1/set.ts b/src/schema/yaml-1.1/set.ts
index b1396fde..bafc3bc6 100644
--- a/src/schema/yaml-1.1/set.ts
+++ b/src/schema/yaml-1.1/set.ts
@@ -76,7 +76,7 @@ export class YAMLSet<T = unknown> extends YAMLMap<T, Scalar<null> | null> {
     ctx?: StringifyContext,
     onComment?: () => void,
     onChompKeep?: () => void
-  ) {
+  ): string {
     if (!ctx) return JSON.stringify(this)
     if (this.hasAllNullValues(true))
       return super.toString(
@@ -87,7 +87,11 @@ export class YAMLSet<T = unknown> extends YAMLMap<T, Scalar<null> | null> {
     else throw new Error('Set items must all have null values')
   }
 
-  static from(schema: Schema, iterable: unknown, ctx: CreateNodeContext) {
+  static from(
+    schema: Schema,
+    iterable: unknown,
+    ctx: CreateNodeContext
+  ): YAMLSet {
     const { replacer } = ctx
     const set = new this(schema)
     if (iterable && Symbol.iterator in Object(iterable))
diff --git a/src/stringify/foldFlowLines.ts b/src/stringify/foldFlowLines.ts
index ea15a47c..b1734645 100644
--- a/src/stringify/foldFlowLines.ts
+++ b/src/stringify/foldFlowLines.ts
@@ -49,7 +49,7 @@ export function foldFlowLines(
     onFold,
     onOverflow
   }: FoldOptions = {}
-) {
+): string {
   if (!lineWidth || lineWidth < 0) return text
   if (lineWidth < minContentWidth) minContentWidth = 0
   const endStep = Math.max(1 + minContentWidth, 1 + lineWidth - indent.length)
diff --git a/src/stringify/stringifyNumber.ts b/src/stringify/stringifyNumber.ts
index 455bc750..b2489953 100644
--- a/src/stringify/stringifyNumber.ts
+++ b/src/stringify/stringifyNumber.ts
@@ -5,7 +5,7 @@ export function stringifyNumber({
   minFractionDigits,
   tag,
   value
-}: Scalar) {
+}: Scalar): string {
   if (typeof value === 'bigint') return String(value)
   const num = typeof value === 'number' ? value : Number(value)
   if (!isFinite(num)) return isNaN(num) ? '.nan' : num < 0 ? '-.inf' : '.inf'
diff --git a/src/stringify/stringifyString.ts b/src/stringify/stringifyString.ts
index 2de6aa37..b52ad9ce 100644
--- a/src/stringify/stringifyString.ts
+++ b/src/stringify/stringifyString.ts
@@ -346,7 +346,7 @@ export function stringifyString(
   ctx: StringifyContext,
   onComment?: () => void,
   onChompKeep?: () => void
-) {
+): string {
   const { implicitKey, inFlow } = ctx
   const ss: StringifyScalar =
     typeof item.value === 'string'