diff --git a/book/08-proof-of-work.md b/book/08-proof-of-work.md
new file mode 100644
index 0000000..257718d
--- /dev/null
+++ b/book/08-proof-of-work.md
@@ -0,0 +1,322 @@
+# Proof of Work
+
+Every event id is a SHA-256 hash. Most of the time that hash is
+whatever it happens to be — nobody cares about the specific bit
+pattern. Proof of work changes that. NIP-13 defines a convention where
+a client burns CPU time searching for a nonce that makes the event id
+start with a target number of leading zero bits. The result is an event
+that carries a verifiable proof of computational effort baked into its
+identity.
+
+The purpose is spam resistance. A relay can require that incoming events
+have, say, 20 leading zero bits. Generating one costs the publisher
+roughly 2^20 hash attempts — a second or two on modern hardware — but
+spamming a thousand events costs a thousand times that. It is not a
+substitute for moderation, but it raises the floor.
+
+The protocol mechanism is a single tag: `["nonce", "<counter>",
+"<target>"]`. The first value is the nonce that was found; the second
+is the difficulty the miner was aiming for. Both are needed: the nonce
+changes the event id (because tags are part of the hash input), and the
+target records intent so that a verifier can distinguish a miner who
+committed to 20 bits of work from one who committed to 4 and got lucky.
+
+This chapter builds three things: a function to count leading zero bits,
+a function to read the validated proof-of-work difficulty from an event,
+and a pair of mining functions that search for a valid nonce and return
+a `HashedEvent` with the proof embedded. The mining API is batch-based:
+callers control the loop, which keeps the library free of
+platform-specific threading or async machinery.
+
+## The module
+
+```rust {file=coracle-lib/src/lib.rs}
+pub mod pow;
+```
+
+```rust {file=coracle-lib/src/pow.rs}
+//! NIP-13 proof of work: difficulty validation and mining.
+//!
+//! [`mine_pow`] blocks until a valid nonce is found. [`mine_pow_batch`]
+//! tries a bounded range of nonces and returns `None` if the batch is
+//! exhausted, giving the caller control over cancellation and
+//! parallelization.
+
+use sha2::{Digest, Sha256};
+
+use crate::events::{Event, HashedEvent, OwnedEvent};
+use crate::tags::{Tag, Tags};
+```
+
+## Counting leading zero bits
+
+Everything else in this module builds on one primitive: counting how many
+leading bits of a byte slice are zero. A hash with 20 leading zero bits
+starts with at least five zero hex characters (20 / 4 = 5). Difficulty
+is measured in bits, not hex characters, because bits give finer
+granularity — you can require 21 bits of work, not just 20 or 24.
+
+The algorithm walks through bytes. Each fully-zero byte contributes
+eight bits. The first non-zero byte contributes its own leading zeros
+(via the `leading_zeros` intrinsic, which compiles to a single CPU
+instruction on most architectures), and then we stop — no byte after
+that can contribute leading zeros.
+
+```rust {file=coracle-lib/src/pow.rs}
+/// Count the number of leading zero bits in a byte slice.
+///
+/// Returns 0 for an empty slice. For a 32-byte SHA-256 hash, the
+/// maximum return value is 256.
+pub fn get_leading_zero_bits(hash: &[u8]) -> u8 {
+    let mut count: u8 = 0;
+    for &byte in hash {
+        if byte == 0 {
+            count += 8;
+        } else {
+            count += byte.leading_zeros() as u8;
+            break;
+        }
+    }
+    count
+}
+```
+
+## Validation
+
+Validating proof of work on an existing event means answering the
+question: how much work did this event *commit to*? That's the minimum
+of two values — the actual leading zero bits in the hash and the
+difficulty claimed in the nonce tag. The hash proves work was done; the
+tag proves intent. A miner who targeted difficulty 4 and happened to
+land on 20 zero bits only committed to 4 bits of work.
+
+The core logic takes just an id and tags so it can be shared across
+event types.
+
+```rust {file=coracle-lib/src/pow.rs}
+/// Return the validated proof-of-work difficulty for an event id and tags.
+///
+/// The result is the minimum of the actual leading zero bits in `id`
+/// and the difficulty target claimed in the `nonce` tag. Returns 0 if
+/// no nonce tag is present.
+pub fn get_pow(id: &[u8; 32], tags: &Tags) -> u8 {
+    let leading = get_leading_zero_bits(id);
+
+    let claimed: u8 = tags
+        .find("nonce")
+        .and_then(|t| t.get(2))
+        .and_then(|s| s.parse().ok())
+        .unwrap_or(0);
+
+    leading.min(claimed)
+}
+```
+
+The nonce tag's third entry (index 2) holds the difficulty target as a
+decimal string. If the tag is absent or the value doesn't parse, the
+claimed target is zero, so `get_pow` returns zero — no verifiable
+commitment was made.
+
+### Methods on event types
+
+Both `HashedEvent` and `Event` carry an id and tags, so both get a
+`get_pow` method that delegates to the free function. This lets callers
+write `event.get_pow() >= 20` regardless of whether the event has been
+signed yet.
+
+```rust {file=coracle-lib/src/pow.rs}
+impl HashedEvent {
+    /// Return the validated proof-of-work difficulty of this event.
+    ///
+    /// The result is the minimum of the actual leading zero bits in the
+    /// event id and the difficulty claimed in the nonce tag.
+    pub fn get_pow(&self) -> u8 {
+        get_pow(&self.id, &self.tags)
+    }
+}
+
+impl Event {
+    /// Return the validated proof-of-work difficulty of this event.
+    ///
+    /// The result is the minimum of the actual leading zero bits in the
+    /// event id and the difficulty claimed in the nonce tag.
+    pub fn get_pow(&self) -> u8 {
+        get_pow(&self.id, &self.tags)
+    }
+}
+```
+
+## Mining
+
+Mining is a brute-force search. For each candidate nonce, the miner
+builds a nonce tag, constructs the canonical serialization that the
+events chapter defined, hashes it, and checks the leading zero bits. If
+the hash meets the target, the search is over; if not, it tries the
+next nonce.
+
+The canonical form is the same JSON array from the events chapter:
+`[0, pubkey, created_at, kind, tags, content]`. The nonce tag is
+appended to the event's existing tags before serialization, so the
+nonce value feeds into the hash. Changing the nonce changes the hash —
+that's the whole mechanism.
+
+Two free functions expose this search at different levels of control,
+and `OwnedEvent` gets methods that delegate to them.
+
+### `mine_pow` — the simple interface
+
+For callers who just want a result and are willing to block until it
+arrives:
+
+```rust {file=coracle-lib/src/pow.rs}
+/// Mine proof of work for an event, blocking until a valid nonce is found.
+///
+/// Appends a `["nonce", "<counter>", "<difficulty>"]` tag to the event's
+/// tags and searches for a nonce that produces an event id with at least
+/// `difficulty` leading zero bits. Returns the resulting `HashedEvent`.
+///
+/// This function does not return until a solution is found. For
+/// cancellation or parallelization, use [`mine_pow_batch`] instead.
+pub fn mine_pow(event: &OwnedEvent, difficulty: u8) -> HashedEvent {
+    let mut start: u64 = 0;
+    loop {
+        let batch_size: u64 = 1_000_000;
+        if let Some(result) = mine_pow_batch(event, difficulty, start, batch_size) {
+            return result;
+        }
+        start += batch_size;
+    }
+}
+```
+
+### `mine_pow_batch` — the batch interface
+
+For callers who need control over when to stop or how to distribute
+work across threads or web workers:
+
+```rust {file=coracle-lib/src/pow.rs}
+/// Try to mine proof of work over a bounded range of nonces.
+///
+/// Searches nonces from `start` to `start + count - 1`. Returns
+/// `Some(HashedEvent)` if a nonce producing at least `difficulty`
+/// leading zero bits is found, or `None` if the entire range is
+/// exhausted without a match.
+///
+/// # Parallelization
+///
+/// To distribute work across N workers, give each worker a
+/// non-overlapping range: worker *i* calls
+/// `mine_pow_batch(event, difficulty, i * chunk, chunk)`.
+/// The first worker to return `Some` wins; the rest can be cancelled
+/// by simply not issuing further batches.
+pub fn mine_pow_batch(
+    event: &OwnedEvent,
+    difficulty: u8,
+    start: u64,
+    count: u64,
+) -> Option<HashedEvent> {
+    let difficulty_str = difficulty.to_string();
+    let mut tags = event.tags.clone();
+    tags.0.push(Tag::new("nonce", ["0", &difficulty_str]));
+    let nonce_idx = tags.0.len() - 1;
+
+    let end = start.saturating_add(count);
+    for nonce in start..end {
+        tags.0[nonce_idx].0[1] = nonce.to_string();
+
+        let canonical = serde_json::json!([
+            0,
+            event.pubkey.to_hex(),
+            event.created_at,
+            event.kind,
+            &tags,
+            &event.content,
+        ])
+        .to_string();
+
+        let id: [u8; 32] = Sha256::digest(canonical.as_bytes()).into();
+
+        if get_leading_zero_bits(&id) >= difficulty {
+            return Some(HashedEvent {
+                content: event.content.clone(),
+                kind: event.kind,
+                tags,
+                created_at: event.created_at,
+                pubkey: event.pubkey,
+                id,
+            });
+        }
+    }
+
+    None
+}
+```
+
+The batch function clones the event's tags once, appends a placeholder
+nonce tag, then mutates the nonce value in place on each iteration.
+The canonical JSON is rebuilt every iteration — the nonce string changes
+each time, so the serialization must too — but the tag vector itself is
+reused rather than reallocated.
+
+The returned `HashedEvent` includes the winning nonce tag in its tags.
+From there it slots into the normal event pipeline: call `.sign()` to
+produce a full `Event` ready for the wire.
+
+### Methods on `OwnedEvent`
+
+For callers who prefer the method style, `OwnedEvent` delegates to the
+free functions:
+
+```rust {file=coracle-lib/src/pow.rs}
+impl OwnedEvent {
+    /// Mine proof of work, blocking until a valid nonce is found.
+    ///
+    /// See [`mine_pow`] for details.
+    pub fn mine_pow(&self, difficulty: u8) -> HashedEvent {
+        mine_pow(self, difficulty)
+    }
+
+    /// Try to mine proof of work over a bounded range of nonces.
+    ///
+    /// See [`mine_pow_batch`] for details.
+    pub fn mine_pow_batch(
+        &self,
+        difficulty: u8,
+        start: u64,
+        count: u64,
+    ) -> Option<HashedEvent> {
+        mine_pow_batch(self, difficulty, start, count)
+    }
+}
+```
+
+## Usage patterns
+
+The split between `mine_pow` and `mine_pow_batch` keeps the library
+code simple while supporting a range of caller strategies:
+
+**Blocking single-threaded** — the common case. `event.mine_pow(20)`
+blocks until it finds a valid nonce and returns the `HashedEvent`.
+
+**Batched with cancellation** — a UI that wants to let the user abort.
+The caller loops over `event.mine_pow_batch(20, cursor, 100_000)`,
+incrementing `cursor` by 100,000 each round. Between rounds it checks
+whether the user pressed cancel.
+
+**Parallel native threads** — each of N threads gets a non-overlapping
+chunk of the nonce space. The first thread to return `Some` wins; the
+rest are abandoned.
+
+**WASM web workers** — the main thread posts a batch range to a worker
+via `postMessage`. The worker calls `mine_pow_batch`, posts the result
+back. To cancel, the main thread simply stops posting new batches. No
+shared memory, no atomics, no platform-specific API in the library.
+
+**Validation** — a relay checking incoming events writes
+`event.get_pow() >= 20`. The method works on both `HashedEvent` and
+`Event`.
+
+## What's next
+
+The next chapter introduces filters — the query language clients use to
+ask relays for events matching a set of criteria.
diff --git a/book/plan/proof-of-work.md b/book/plan/proof-of-work.md
new file mode 100644
index 0000000..f5b1666
--- /dev/null
+++ b/book/plan/proof-of-work.md
@@ -0,0 +1,125 @@
+# Plan: Proof of Work
+
+## Topic Summary
+
+Full implementation of NIP-13 proof-of-work: validation and generation. The mining function
+receives an `OwnedEvent` reference with a target difficulty and hashes until the difficulty
+is achieved, returning a `HashedEvent`. The API is batch-based and pure — no threading, no
+async, no platform-specific code. Callers control the loop and can parallelize or cancel by
+managing batch ranges externally.
+
+## Chapter Outline
+
+1. **Introduction** — What PoW means in nostr: leading zero bits on the SHA-256 event id.
+   Why it exists (spam resistance, relay filtering, signal of effort). Reference NIP-13.
+
+2. **Module setup** — Add `pub mod pow;` to `coracle-lib/src/lib.rs`. Module imports.
+
+3. **Counting leading zero bits** — `get_leading_zero_bits(hash: &[u8]) -> u8`. Pure utility
+   that iterates bytes: full zero byte = +8 bits, partial byte uses `leading_zeros()`. This
+   is the foundation everything else builds on.
+
+4. **The nonce tag** — NIP-13 specifies a `["nonce", "<counter>", "<difficulty>"]` tag. Explain
+   that the nonce is part of the event content that gets hashed — changing it changes the id.
+   Show how to add/read the tag using the existing `Tags` type.
+
+5. **Validation** — `check_pow(event: &HashedEvent, difficulty: u8) -> bool`. Checks that the
+   event id has at least `difficulty` leading zero bits AND that the nonce tag's claimed
+   difficulty is at least `difficulty`. Both checks are needed: the id check proves the work
+   was done, the tag check proves the miner intended at least this difficulty.
+
+6. **Mining** — `mine_pow(event: &OwnedEvent, difficulty: u8, start: Option<u64>, count: Option<u64>) -> Option<HashedEvent>`.
+   Clones the event's tags, appends/updates a nonce tag, hashes, checks difficulty. Iterates
+   nonces from `start` (default 0) for up to `count` attempts (default unbounded). Returns
+   `Some(HashedEvent)` on success, `None` if the batch is exhausted.
+
+7. **Usage patterns** — Brief prose (not tangled code) showing:
+   - Simple: `mine_pow(&event, 20, None, None)` — blocks until done
+   - Batched: loop calling with `Some(cursor)` and `Some(100_000)`
+   - Parallel: N threads/workers with non-overlapping ranges
+   - WASM: worker runs batches, main thread stops sending to cancel
+
+8. **What's next** — Transition to filters chapter.
+
+## API Design
+
+```rust
+/// Count the leading zero bits in a byte slice.
+pub fn get_leading_zero_bits(hash: &[u8]) -> u8
+
+/// Check that an event meets a minimum proof-of-work difficulty.
+/// Returns true if the event id has at least `difficulty` leading zero bits
+/// AND the nonce tag claims at least `difficulty`.
+pub fn check_pow(event: &HashedEvent, difficulty: u8) -> bool
+
+/// Mine proof-of-work for an event.
+///
+/// Tries nonces starting from `start` (default 0) for up to `count` attempts
+/// (default unbounded). Returns `Some(HashedEvent)` with the nonce tag included
+/// if a valid nonce is found, `None` if the batch is exhausted.
+pub fn mine_pow(
+    event: &OwnedEvent,
+    difficulty: u8,
+    start: Option<u64>,
+    count: Option<u64>,
+) -> Option<HashedEvent>
+```
+
+## Code Organization
+
+- **Crate**: `coracle-lib`
+- **Module**: `coracle-lib/src/pow.rs`
+- **Exports**: `get_leading_zero_bits`, `check_pow`, `mine_pow`
+- **Dependencies on existing code**: `OwnedEvent`, `HashedEvent` from `events`, `Tags` from `tags`
+- Add `pub mod pow;` to `coracle-lib/src/lib.rs`
+
+## Dependencies
+
+No new external crates. SHA-256 (`sha2`) and hex encoding are already available from the
+events chapter. Leading zero bit counting uses only `u8::leading_zeros()` from std.
+
+## Narrative Notes
+
+- **Why both id check and tag check**: An event with 25 leading zeros but a nonce tag claiming
+  difficulty 10 only committed to 10 bits of work — the extra zeros are luck. Relays that
+  require difficulty 20 should reject it. Explain this clearly.
+
+- **Why batch-based**: The chapter should explain the design choice. A blocking `loop until
+  found` function can't be cancelled and can't be parallelized. By exposing start/count, the
+  library stays pure and platform-agnostic while giving callers full control. Show how this
+  maps to threads (native) and workers (WASM).
+
+- **Nonce tag placement**: The tag must be part of the serialized event before hashing. The
+  mining loop adds the tag, hashes, checks, and either returns or tries the next nonce. Work
+  on a clone of the input's tags — don't mutate the original.
+
+- **Difficulty semantics**: Difficulty is measured in leading zero *bits*, not bytes or hex
+  characters. Difficulty 20 means the first 20 bits of the 256-bit hash are zero. This allows
+  fine-grained difficulty that isn't locked to 4-bit (hex) or 8-bit (byte) boundaries.
+
+## Design Decisions
+
+1. **Batch-based API over blocking loop**: Enables cancellation and parallelization without
+   platform-specific code. Callers who want simple blocking behavior pass `None` for both
+   start and count. Research showed rust-nostr uses a tight blocking loop with optional
+   multi-threading via feature flags; welshman uses Web Workers. Our approach avoids both
+   by pushing the concurrency concern to the caller.
+
+2. **No prefix generation**: `get_prefixes_for_difficulty()` (seen in rust-nostr and nostr-tools)
+   converts bit difficulty to hex prefixes for relay querying. Deferred — it's orthogonal to
+   mining/validation and can be added later if needed.
+
+3. **Nonce as u64**: rust-nostr uses u128, but u64 gives 1.8×10¹⁹ attempts — more than enough
+   for any practical difficulty. Keeps the tag string shorter and matches JS number limits
+   for WASM interop.
+
+4. **Clone, don't mutate**: `mine_pow` takes `&OwnedEvent` and clones internally. The caller
+   keeps their original event unchanged. This matches the functional style of the event
+   pipeline (each step returns a new type).
+
+5. **check_pow validates both id and tag**: Following NIP-13 semantics. The id check proves
+   the work; the tag check proves intent. Both are needed for correct validation.
+
+## Open Questions
+
+None — scope is well-defined and all design decisions are resolved.
diff --git a/book/research/proof-of-work.md b/book/research/proof-of-work.md
new file mode 100644
index 0000000..c9a6629
--- /dev/null
+++ b/book/research/proof-of-work.md
@@ -0,0 +1,195 @@
+# Research: Proof of Work
+
+## Topic Summary
+
+Full implementation of NIP-13 proof-of-work: validation/querying and generation. The mining function receives an `OwnedEvent` with a target difficulty and hashes until the difficulty is achieved, returning a `HashedEvent`. The design should support running in a separate thread (native) or a Web Worker (wasm).
+
+## Philosophy
+
+From `ref/building-nostr`:
+
+- PoW is framed as an **optional, client-level heuristic** — not a protocol requirement. Users can "use web of trust or proof of work heuristics to filter posts."
+- Clients should have user-configurable policies for handling adversarial data. PoW is one tool among several (reputation, payment, WoT).
+- Economic spam prevention (relay charging) is presented as an alternative to computational PoW.
+- NIP-13 is not mentioned by name; the philosophy emphasizes user agency and optional mechanisms over mandated solutions.
+
+## Reference Implementation Analysis
+
+### applesauce
+
+No PoW implementation found. The applesauce libraries focus on client UI utilities and do not include NIP-13 support.
+
+### ndk
+
+No PoW mining or validation in NDK core. NDK does parse `min_pow_difficulty` from NIP-11 relay info documents (`NDKRelayInformation.limitation.min_pow_difficulty`), but does not act on it. PoW mining is delegated to external packages.
+
+### nostr-gadgets
+
+No PoW implementation found. The library focuses on hints scoring, database utilities, event sets, and outbox logic.
+
+### nostrlib
+
+No PoW-specific findings from the Go library search. The library may handle it elsewhere but no dedicated NIP-13 module was found.
+
+### nostr-tools
+
+**File:** `nip13.ts`
+
+Complete standalone NIP-13 implementation:
+
+- **`getPow(hex: string): number`** — Counts leading zero bits from hex string by iterating 8-bit nibbles.
+- **`getPowFromBytes(hash: Uint8Array): number`** — Byte-based version using `Math.clz32()` for the partial byte.
+- **`minePow(unsigned: UnsignedEvent, difficulty: number)`** — Synchronous mining on main thread:
+  - Appends `["nonce", count, difficulty]` tag
+  - Increments nonce counter until SHA-256 hash meets difficulty threshold
+  - Uses `@noble/hashes` for SHA-256
+  - Mutates `created_at` when time rolls over
+  - Returns event with computed `id` field
+
+**Design:** Simple, synchronous, single-threaded. No worker support. Minimal dependencies.
+
+**Test vectors:** Validates `getPow` against known hashes with specific difficulties (0–73 bits). Tests `minePow` with difficulty=10.
+
+### rust-nostr
+
+**Files:**
+- `crates/nostr/src/nips/nip13.rs` — Core PoW utilities
+- `crates/nostr/src/event/builder.rs` — Mining loop
+- `crates/nostr/src/event/id.rs` — Validation
+- `crates/nostr/src/event/tag/standard.rs` — POW tag structure
+
+**Data Structures:**
+```rust
+TagStandard::POW { nonce: u128, difficulty: u8 }
+// Serializes to: ["nonce", "<nonce>", "<difficulty>"]
+
+EventBuilder { pow: Option<u8>, ... }
+```
+
+**Core Algorithm — `get_leading_zero_bits<T: AsRef<[u8]>>(h: T) -> u8`:**
+- Iterates bytes: full zero byte → +8 bits; non-zero byte → `leading_zeros()` CPU intrinsic; return
+- Range 0–255
+
+**Prefix Generation — `get_prefixes_for_difficulty(bits: u8) -> Vec<String>`:**
+- Converts bit difficulty to valid hex prefixes for filtering/querying
+- Formula: `prefix_count = 2^(hex_bits - difficulty_bits)`
+
+**Single-Threaded Mining (`mine_pow_single_thread`):**
+- Increments nonce from 0
+- For each nonce: push POW tag → compute EventId (SHA-256) → check leading zeros ≥ difficulty → pop tag if fail
+- Returns `UnsignedEvent` on success
+
+**Multi-Threaded Mining (`mine_pow_multi_thread`, feature `pow-multi-thread`):**
+- Spawns `thread::available_parallelism()` threads
+- Each thread: starting nonce = `thread_id`, stride = `num_threads`
+- Coordination: `Arc<AtomicBool>` with `Ordering::Relaxed`
+- First thread to find solution signals others to stop
+- Main thread busy-waits on atomic flag
+- Falls back to single-threaded if 1 core or spawn failure
+
+**Validation:**
+```rust
+impl EventId {
+    pub fn check_pow(&self, difficulty: u8) -> bool {
+        nip13::get_leading_zero_bits(self.as_bytes()) >= difficulty
+    }
+}
+```
+
+**Relay enforcement:** `nostr-relay-builder` checks `min_pow` before accepting events.
+
+**Design decisions:**
+- `nonce: u128` — virtually inexhaustible nonce space
+- `difficulty: u8` — matches SHA-256 bit width
+- Feature-gated multi-threading keeps `no_std` compatibility
+- Busy-wait polling (not ideal but simple)
+- Timestamp captured once before mining, shared across threads
+
+### welshman
+
+**File:** `packages/util/src/Pow.ts`
+
+Worker-based asynchronous mining:
+
+- **`makePow(event: OwnedEvent, difficulty: number): ProofOfWork`**
+  - Returns `{ worker: Worker, result: Promise<HashedEvent> }`
+  - Creates Web Worker from inline `Blob` URL
+  - Worker receives event + difficulty via `postMessage`
+  - Worker runs mining loop using `crypto.subtle.digest("SHA-256", ...)`
+  - Nonce tag mutated in-place for performance: `tag[1] = count.toString()`
+  - Supports `start` and `step` parameters for distributing across multiple workers
+
+- **`getPow(event: HashedEvent): number`** — Validates difficulty from event hash. Counts leading zero bytes, then uses `Math.clz32()` on final byte.
+
+- **`estimateWork(difficulty: number)`** — Cost estimation using benchmark: `benchmark_ms * 2^(difficulty - benchmarkDifficulty)`. `benchmarkDifficulty = 15`.
+
+**Integration in `thunk.ts`:**
+- PoW applied before signing (necessary because nonce changes the event ID)
+- For gift-wrapped events (NIP-59): PoW on the wrapper
+- Uses `AbortSignal.timeout(30_000)` for timeout protection
+- Logs warning if event already signed (PoW would change ID, invalidating signature)
+
+**Design:** Non-blocking via Workers. Single worker by default but architecture supports multi-worker distribution via start/step. Uses Web Crypto API (available in workers).
+
+## Common Patterns
+
+1. **Difficulty metric:** All implementations use leading zero bits in SHA-256 hash (NIP-13 standard). Not byte-aligned — allows fine-grained difficulty.
+
+2. **Tag format:** Universal `["nonce", "<counter>", "<target_difficulty>"]` tag.
+
+3. **Mining loop:** Increment nonce, recompute hash, check leading zeros. Simple brute force — no shortcuts possible.
+
+4. **PoW before signing:** All implementations compute PoW before the event is signed, since the nonce tag changes the event ID which is what gets signed.
+
+5. **Leading zero counting:** Two approaches:
+   - Byte iteration + CPU intrinsic (`leading_zeros()` / `Math.clz32()`)
+   - Hex string nibble iteration (nostr-tools)
+
+6. **Parallelism strategies diverge:**
+   - rust-nostr: OS threads with atomic bool coordination
+   - welshman: Web Workers with message passing
+   - nostr-tools: no parallelism (synchronous)
+
+## Considerations for Our Implementation
+
+### API Design
+
+The chapter should take an `OwnedEvent` (has pubkey but no hash yet) and return a `HashedEvent` (has computed ID meeting difficulty). This fits naturally into the event lifecycle from chapter 05.
+
+The mining function should be **pure and blocking** — it takes inputs and returns a result. Threading/worker dispatch is the caller's responsibility. This keeps the core function platform-agnostic:
+- Native: caller wraps in `std::thread::spawn` or `tokio::spawn_blocking`
+- WASM: caller runs in a Web Worker
+
+### Validation
+
+Two levels:
+1. `get_leading_zero_bits(hash: &[u8]) -> u8` — pure utility
+2. `check_pow(event: &HashedEvent, difficulty: u8) -> bool` — checks event's nonce tag difficulty matches actual hash difficulty
+
+### Querying
+
+`get_prefixes_for_difficulty(difficulty: u8) -> Vec<String>` enables relay-side filtering by event ID prefix. Useful for REQ filters.
+
+### Dependencies
+
+- SHA-256 already available from the events chapter
+- No additional crates needed for single-threaded PoW
+- `u128` nonce type is standard Rust
+
+### Threading Considerations
+
+Rather than building threading into the mining function:
+- Keep `mine_pow(event: OwnedEvent, difficulty: u8) -> HashedEvent` as a blocking function
+- Document how callers can parallelize (thread per core, strided nonces via start/step parameters)
+- For WASM: the function runs inside a worker; the host page dispatches to it
+
+This matches welshman's approach and avoids platform-specific code in the core library.
+
+### Nonce Strategy
+
+Support `start` and `step` parameters to enable callers to distribute work:
+```rust
+mine_pow(event: OwnedEvent, difficulty: u8, start: u64, step: u64) -> HashedEvent
+```
+- Single thread: `start=0, step=1`
+- N threads: thread i uses `start=i, step=N`
diff --git a/coracle-lib/tests/pow.rs b/coracle-lib/tests/pow.rs
new file mode 100644
index 0000000..d8f4014
--- /dev/null
+++ b/coracle-lib/tests/pow.rs
@@ -0,0 +1,217 @@
+use coracle_lib::events::{EventContent, OwnedEvent};
+use coracle_lib::keys::SecretKey;
+use coracle_lib::pow::{get_leading_zero_bits, get_pow, mine_pow, mine_pow_batch};
+use coracle_lib::tags::{Tag, Tags};
+
+fn fixed_secret() -> SecretKey {
+    let bytes: [u8; 32] = [
+        1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
+        25, 26, 27, 28, 29, 30, 31, 32,
+    ];
+    SecretKey::from_hex(&hex::encode(bytes)).unwrap()
+}
+
+fn test_event() -> OwnedEvent {
+    EventContent::new("hello nostr", Tags::new())
+        .kind(1)
+        .stamp(1_700_000_000)
+        .own(fixed_secret().public_key())
+}
+
+// --- get_leading_zero_bits ---
+
+#[test]
+fn leading_zeros_empty_slice() {
+    assert_eq!(get_leading_zero_bits(&[]), 0);
+}
+
+#[test]
+fn leading_zeros_all_zeros() {
+    assert_eq!(get_leading_zero_bits(&[0, 0, 0, 0]), 32);
+}
+
+#[test]
+fn leading_zeros_first_byte_nonzero() {
+    assert_eq!(get_leading_zero_bits(&[0x80, 0x00]), 0);
+    assert_eq!(get_leading_zero_bits(&[0x01, 0x00]), 7);
+    assert_eq!(get_leading_zero_bits(&[0x0F]), 4);
+}
+
+#[test]
+fn leading_zeros_with_zero_prefix() {
+    assert_eq!(get_leading_zero_bits(&[0x00, 0x01]), 15);
+    assert_eq!(get_leading_zero_bits(&[0x00, 0x00, 0x80]), 16);
+    assert_eq!(get_leading_zero_bits(&[0x00, 0x00, 0x00, 0x01]), 31);
+}
+
+#[test]
+fn leading_zeros_known_hash() {
+    // "000006d8..." → 0x00, 0x00, 0x06 → 16 + 5 = 21
+    let hash = hex::decode("000006d8c378af1779d2feebc7603a125d99eca0ccf1085959b307f64e5dd358")
+        .unwrap();
+    assert_eq!(get_leading_zero_bits(&hash), 21);
+}
+
+// --- get_pow (free function) ---
+
+#[test]
+fn get_pow_returns_min_of_hash_and_claim() {
+    let event = test_event();
+    let hashed = mine_pow(&event, 8);
+    // The free function should return at least 8
+    assert!(get_pow(&hashed.id, &hashed.tags) >= 8);
+}
+
+#[test]
+fn get_pow_zero_without_nonce_tag() {
+    let hashed = test_event().hash();
+    assert_eq!(get_pow(&hashed.id, &hashed.tags), 0);
+}
+
+#[test]
+fn get_pow_capped_by_claimed_difficulty() {
+    // Mine at difficulty 4 — even if hash has more leading zeros,
+    // get_pow returns at most 4
+    let event = test_event();
+    let hashed = mine_pow(&event, 4);
+    assert!(get_pow(&hashed.id, &hashed.tags) >= 4);
+    // Actual leading zeros might exceed 4, but get_pow is min(leading, claimed)
+    assert_eq!(get_pow(&hashed.id, &hashed.tags), 4);
+}
+
+// --- HashedEvent::get_pow method ---
+
+#[test]
+fn hashed_event_get_pow_method() {
+    let event = test_event();
+    let hashed = mine_pow(&event, 8);
+    assert!(hashed.get_pow() >= 8);
+}
+
+#[test]
+fn hashed_event_get_pow_zero_without_nonce() {
+    let hashed = test_event().hash();
+    assert_eq!(hashed.get_pow(), 0);
+}
+
+// --- Event::get_pow method ---
+
+#[test]
+fn signed_event_get_pow_method() {
+    let sk = fixed_secret();
+    let event = test_event();
+    let hashed = mine_pow(&event, 8);
+    let sig = sk.sign(&hashed.id);
+    let signed = hashed.sign(sig);
+    assert!(signed.get_pow() >= 8);
+}
+
+// --- OwnedEvent::mine_pow method ---
+
+#[test]
+fn owned_event_mine_pow_method() {
+    let event = test_event();
+    let result = event.mine_pow(8);
+    assert!(result.get_pow() >= 8);
+}
+
+// --- OwnedEvent::mine_pow_batch method ---
+
+#[test]
+fn owned_event_mine_pow_batch_method() {
+    let event = test_event();
+    let result = event.mine_pow_batch(1, 0, 1_000_000);
+    assert!(result.is_some());
+    assert!(result.unwrap().get_pow() >= 1);
+}
+
+// --- mine_pow (free function) ---
+
+#[test]
+fn mine_pow_returns_valid_result() {
+    let event = test_event();
+    let result = mine_pow(&event, 8);
+
+    assert!(get_leading_zero_bits(&result.id) >= 8);
+
+    let nonce_tag = result.tags.find("nonce").expect("should have nonce tag");
+    assert_eq!(nonce_tag.get(2), Some("8"));
+
+    let _nonce: u64 = nonce_tag.value().parse().expect("nonce should be a number");
+}
+
+#[test]
+fn mine_pow_preserves_event_fields() {
+    let event = test_event();
+    let result = mine_pow(&event, 4);
+
+    assert_eq!(result.content, event.content);
+    assert_eq!(result.kind, event.kind);
+    assert_eq!(result.created_at, event.created_at);
+    assert_eq!(result.pubkey, event.pubkey);
+}
+
+#[test]
+fn mine_pow_preserves_existing_tags() {
+    let mut event = test_event();
+    event.tags.0.push(Tag::new("t", ["nostr"]));
+    let result = mine_pow(&event, 4);
+
+    assert!(result.tags.find("t").is_some());
+    assert!(result.tags.find("nonce").is_some());
+}
+
+#[test]
+fn mine_pow_does_not_mutate_input() {
+    let event = test_event();
+    let tags_before = event.tags.clone();
+    let _result = mine_pow(&event, 4);
+    assert_eq!(event.tags, tags_before);
+}
+
+// --- mine_pow_batch (free function) ---
+
+#[test]
+fn mine_pow_batch_returns_none_when_exhausted() {
+    let event = test_event();
+    let result = mine_pow_batch(&event, 64, 0, 10);
+    assert!(result.is_none());
+}
+
+#[test]
+fn mine_pow_batch_finds_solution_in_range() {
+    let event = test_event();
+    let result = mine_pow_batch(&event, 1, 0, 1_000_000);
+    assert!(result.is_some());
+    assert!(get_leading_zero_bits(&result.unwrap().id) >= 1);
+}
+
+#[test]
+fn mine_pow_batch_respects_start_offset() {
+    let event = test_event();
+    let a = mine_pow_batch(&event, 4, 0, 1_000_000);
+    let b = mine_pow_batch(&event, 4, 500_000, 1_000_000);
+
+    assert!(a.is_some());
+    assert!(b.is_some());
+
+    let nonce_a = a.unwrap().tags.find("nonce").unwrap().value().to_string();
+    let nonce_b = b.unwrap().tags.find("nonce").unwrap().value().to_string();
+    assert_ne!(nonce_a, nonce_b);
+}
+
+// --- Integration: mine then sign then verify ---
+
+#[test]
+fn mined_event_can_be_signed_and_verified() {
+    let sk = fixed_secret();
+    let event = test_event();
+    let hashed = mine_pow(&event, 8);
+
+    let sig = sk.sign(&hashed.id);
+    let signed = hashed.sign(sig);
+
+    assert!(signed.verify_id());
+    signed.verify().expect("mined and signed event should verify");
+    assert!(signed.get_pow() >= 8);
+}
diff --git a/coracle-wasm/src/lib.rs b/coracle-wasm/src/lib.rs
index ab510f8..f36cd3b 100644
--- a/coracle-wasm/src/lib.rs
+++ b/coracle-wasm/src/lib.rs
@@ -8,7 +8,7 @@
 use wasm_bindgen::prelude::*;
 
 use coracle_lib::encryption as ce;
-use coracle_lib::event as cev;
+use coracle_lib::events as cev;
 use coracle_lib::keys as ck;
 
 fn js_err<E: std::fmt::Display>(e: E) -> JsError {
@@ -181,16 +181,24 @@ impl Event {
         created_at: u64,
         sk: &SecretKey,
     ) -> Result<Event, JsError> {
-        let tags: Vec<Vec<String>> =
+        use coracle_lib::tags::{Tag, Tags};
+
+        let raw_tags: Vec<Vec<String>> =
             serde_wasm_bindgen::from_value(tags).map_err(|e| JsError::new(&e.to_string()))?;
-        // coracle-lib's SecretKey hides the inner secp type behind a
-        // crate-private accessor, so round-trip through hex to hand
-        // Event::new the low-level key it wants.
-        let bytes = hex::decode(sk.0.to_hex()).map_err(js_err)?;
-        let secp_sk = secp256k1::SecretKey::from_slice(&bytes).map_err(js_err)?;
-        Ok(Event(cev::Event::new(
-            kind, content, tags, created_at, &secp_sk,
-        )))
+        let tags = Tags::from(
+            raw_tags
+                .into_iter()
+                .map(|v| Tag::from(v))
+                .collect::<Vec<_>>(),
+        );
+
+        let hashed = cev::EventContent::new(content, tags)
+            .kind(kind)
+            .stamp(created_at)
+            .own(sk.0.public_key())
+            .hash();
+        let sig = sk.0.sign(&hashed.id);
+        Ok(Event(hashed.sign(sig)))
     }
 
     /// Parse an event from its JSON representation.
@@ -209,12 +217,12 @@ impl Event {
 
     #[wasm_bindgen(getter)]
     pub fn id(&self) -> String {
-        self.0.id.clone()
+        hex::encode(self.0.id)
     }
 
     #[wasm_bindgen(getter)]
     pub fn pubkey(&self) -> String {
-        self.0.pubkey.clone()
+        self.0.pubkey.to_hex()
     }
 
     #[wasm_bindgen(getter, js_name = createdAt)]
@@ -234,7 +242,7 @@ impl Event {
 
     #[wasm_bindgen(getter)]
     pub fn sig(&self) -> String {
-        self.0.sig.clone()
+        hex::encode(self.0.sig)
     }
 
     #[wasm_bindgen(getter)]
@@ -242,24 +250,15 @@ impl Event {
         serde_wasm_bindgen::to_value(&self.0.tags).map_err(|e| JsError::new(&e.to_string()))
     }
 
-    /// Canonical `[0, pubkey, created_at, kind, tags, content]` serialization.
-    #[wasm_bindgen]
-    pub fn serialize(&self) -> String {
-        self.0.serialize()
-    }
-
-    #[wasm_bindgen(js_name = computeId)]
-    pub fn compute_id(&self) -> String {
-        self.0.compute_id()
-    }
-
-    #[wasm_bindgen(js_name = idIsValid)]
-    pub fn id_is_valid(&self) -> bool {
-        self.0.id_is_valid()
-    }
-
+    /// Verify both the id and the Schnorr signature.
     #[wasm_bindgen]
     pub fn verify(&self) -> bool {
-        self.0.verify()
+        self.0.verify().is_ok()
+    }
+
+    /// Check whether the recomputed id matches the stored id.
+    #[wasm_bindgen(js_name = verifyId)]
+    pub fn verify_id(&self) -> bool {
+        self.0.verify_id()
     }
 }