diff --git a/src/caching.ts b/src/caching.ts
index 2c47d48..64206e5 100644
--- a/src/caching.ts
+++ b/src/caching.ts
@@ -24,12 +24,17 @@ import {
 import type { ProcExecutor, ProcRequest, ProcResult } from "./contract.ts";
 import { procRequestSchema } from "./contract.ts";
 
+/** A keyed store of {@link ProcResult}s backing a caching executor. */
 export interface ProcCache {
+  /** The cached result for `key`, or `undefined` on a miss. */
   get(key: string): ProcResult | undefined;
+  /** Cache `value` under `key`. */
   set(key: string, value: ProcResult): void;
+  /** Drop everything. */
   clear(): void;
 }
 
+/** A simple in-memory {@link ProcCache} (a `Map`); not persisted across processes. */
 export function inMemoryProcCache(): ProcCache {
   const map = new Map<string, ProcResult>();
   return {
@@ -64,16 +69,21 @@ function cacheKey(req: ProcRequest): string {
   });
 }
 
+/** A {@link ProcExecutor} that memoizes cacheable requests, with an explicit drop. */
 export interface CachingProcExecutor extends ProcExecutor {
   /** Drop all cached results — the next read of each re-derives lazily. */
   invalidate(): void;
 }
 
+/** Options for {@link cachingProcExecutor}. */
 export interface CachingProcOptions {
+  /** The backing store (defaults to {@link inMemoryProcCache}). */
   cache?: ProcCache;
+  /** Predicate deciding which requests may be cached (defaults to {@link policyCacheable}). */
   isCacheable?: (req: ProcRequest) => boolean;
 }
 
+/** Wrap an executor so cacheable requests are memoized; returns a {@link CachingProcExecutor}. */
 export function cachingProcExecutor(
   inner: ProcExecutor,
   opts: CachingProcOptions = {},
diff --git a/src/capture.ts b/src/capture.ts
index ad5bfc8..b5cec39 100644
--- a/src/capture.ts
+++ b/src/capture.ts
@@ -21,27 +21,37 @@ import * as fs from "node:fs";
 import * as os from "node:os";
 import * as path from "node:path";
 
+/** Result of a temp-file-backed spawn capture (no in-memory output ceiling). */
 export type SpawnCaptureResult = {
+  /** Exit code, or `null` if terminated by a signal. */
   status: number | null;
+  /** Terminating signal, or `null`. */
   signal: NodeJS.Signals | null;
   /** Fully-read child stdout — no in-memory ceiling. */
   stdout: string;
+  /** Fully-read child stderr. */
   stderr: string;
+  /** A spawn error (e.g. ENOENT, ETIMEDOUT), if any. */
   error?: Error | undefined;
 };
 
+/** Options for {@link spawnCapture}. */
 export type SpawnCaptureOptions = {
+  /** Working directory for the child. */
   cwd?: string | undefined;
+  /** Environment for the child. */
   env?: NodeJS.ProcessEnv | undefined;
   /** ms; passed through to spawnSync. */
   timeout?: number | undefined;
 };
 
+/** The {@link spawnCapture} signature — an injectable capture seam. */
 export type SpawnCaptureFn = (
   cmd: readonly string[],
   options?: SpawnCaptureOptions,
 ) => SpawnCaptureResult;
 
+/** Run a command capturing stdout/stderr via temp files (no in-memory cap — for output that overflows spawnSync's buffer). */
 export const spawnCapture: SpawnCaptureFn = (cmd, options = {}) => {
   const [file, ...args] = cmd;
   const dir = fs.mkdtempSync(path.join(os.tmpdir(), "prx-spawn-"));
@@ -111,6 +121,7 @@ export function captureFailureDetail(r: SpawnCaptureResult): string {
   return r.error?.message ?? (r.signal ? `killed by ${r.signal}` : (r.stderr || "").trim());
 }
 
+/** {@link SpawnCaptureOptions} plus stdin + per-chunk streaming callbacks. */
 export type StreamCaptureOptions = SpawnCaptureOptions & {
   /** Serializable stdin written to the child then closed (no live stream). */
   stdin?: string | undefined;
diff --git a/src/contract.ts b/src/contract.ts
index ab8d8dc..1351917 100644
--- a/src/contract.ts
+++ b/src/contract.ts
@@ -20,6 +20,7 @@ import { processEnv } from "@bounded-systems/env";
 
 import { streamCapture } from "./capture.ts";
 
+/** Zod schema validating a {@link ProcRequest} (command + args + cwd/env/stdin/timeout/stdio). */
 export const procRequestSchema = z.object({
   command: z.string().min(1),
   args: z.array(z.string()).default([]),
@@ -30,12 +31,18 @@ export const procRequestSchema = z.object({
   stdio: z.enum(["pipe", "inherit"]).default("pipe"),
 });
 
+/** A subprocess request: the command to run and how (parsed from {@link procRequestSchema}). */
 export type ProcRequest = z.input<typeof procRequestSchema>;
 
+/** The outcome of a subprocess: exit status, captured streams, and terminating signal. */
 export interface ProcResult {
+  /** Exit code (or a signal-derived status when killed). */
   readonly status: number;
+  /** Captured standard output. */
   readonly stdout: string;
+  /** Captured standard error. */
   readonly stderr: string;
+  /** The signal that terminated the process, or `null`. */
   readonly signal: string | null;
 }
 
@@ -44,6 +51,7 @@ export interface ProcResult {
  * ship the request over a wire and run it elsewhere — the contract is identical.
  */
 export interface ProcExecutor {
+  /** Run `req` and resolve its {@link ProcResult}. */
   exec(req: ProcRequest): Promise<ProcResult>;
 }
 
diff --git a/src/index.ts b/src/index.ts
index 8acf97c..9b7f2f8 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -33,16 +33,23 @@ export {
   captureFailureDetail,
 } from "./capture.ts";
 
+/** The captured result of a {@link CommandRunner} run. */
 export type CommandResult = {
+  /** Captured standard output. */
   stdout: string;
+  /** Captured standard error. */
   stderr: string;
+  /** Exit code (signal-derived when killed). */
   status: number;
 };
 
+/** Options for a {@link CommandRunner} run. */
 export interface RunOptions {
+  /** Working directory for the child. */
   cwd?: string;
   /** When not false (default), a non-zero exit throws. */
   check?: boolean;
+  /** Environment for the child (defaults to the sanctioned `processEnv()`). */
   env?: NodeJS.ProcessEnv;
   /**
    * "pipe" (default) captures stdout/stderr into the result; "inherit" wires
@@ -72,6 +79,7 @@ function signalExitStatus(signal: NodeJS.Signals | string | null): number {
   return 128 + (typeof num === "number" ? num : 0);
 }
 
+/** The default {@link CommandRunner}: a synchronous `spawnSync` with capture, timeout, and (by default) throw-on-nonzero-exit. */
 export const defaultRunner: CommandRunner = (cmd, options = {}) => {
   const [file, ...args] = cmd;
   if (!file) {
diff --git a/src/spawn-detached.ts b/src/spawn-detached.ts
index 1e0930c..2b80104 100644
--- a/src/spawn-detached.ts
+++ b/src/spawn-detached.ts
@@ -14,8 +14,11 @@ import { closeSync, openSync } from "node:fs";
 
 import { processEnv } from "@bounded-systems/env";
 
+/** Options for {@link spawnDetached} — a child that outlives the parent. */
 export type SpawnDetachedOptions = {
+  /** Working directory for the child. */
   cwd?: string;
+  /** Environment for the child. */
   env?: NodeJS.ProcessEnv;
   /**
    * When set, the child's stdout+stderr are appended to this file (created if
@@ -25,6 +28,7 @@ export type SpawnDetachedOptions = {
   logPath?: string;
 };
 
+/** Result of {@link spawnDetached}: the detached child's process id. */
 export type SpawnDetachedResult = { pid: number };
 
 /**