Rules

• Move every letter from the rack into the blocks. Each letter is used exactly once.
• Words read left to right (across) and top to bottom (down). There are no diagonal words.
• Every across and down run of three or more blocks must be a word from this game's word list.
• Every word has a clue. The clue bar under the board shows the clue for the highlighted word. Tap a block to see its word's clue, use the arrows to flip through them, or tap the clue to see the full list.
• Boards start at 3×3 and grow step by step up to 8×8, with longer words as you go. Each level opens when you've solved the one before it.
• After level 1,000 the game keeps going with randomly generated levels (5×5 to 8×8), so the puzzles never run out.
• Where an across word crosses a down word they share one block, and that block holds one letter.
• Some boards have gaps. Empty space is not part of the puzzle and can't hold a letter.
• Any arrangement that makes every word valid counts as solved. A puzzle can have more than one solution. Clues describe one solution; a different real word that fits also counts, and the clue bar marks it as your own word.
• Early levels start with a few starter letters already locked in place (darker blocks with a dot). They taper off as you get the hang of it. For a real challenge, turn them off in Settings (or "Solve from scratch" in the pause menu) and every board starts empty.
• When a full row or column isn't a word, it gets a ✕ and a pink tint, and the message under the board names it.
• No timers, no lives. Undo and experiment as much as you like.

Controls

• Drag a letter onto a block. Dropping on a filled block swaps the two letters.
• Tap a letter, then tap a block. Or tap an empty block first, then the letter you want there.
• Drag or tap a placed letter back onto the rack to return it.
• Keyboard: Tab between board and rack, arrow keys to move, Enter or Space to pick up and place, Escape to cancel.
• Hint opens four kinds of help. Which letters? lights up the rack letters that finish a word, without saying where. Show a letter reveals one block. Show a word reveals a whole word and can place it for you. Check my letters finds any letter that's in the wrong place. Select a block or letter first to aim the hint at it. Hints are free and only counted in your stats.
• The buttons under the rack: Undo takes back your last move, Reset sends every letter back to the rack, Shuffle mixes up the rack, and Hint opens the hint menu.

The word list

WordPebble accepts only the words in its own list, not every English word. It has 79,000 words of 3 to 8 letters, so plurals, verb forms and less familiar words count too. Puzzle answers are drawn from the most familiar words, each with a hand-written clue. Difficulty is estimated from board size and word familiarity and hasn't been playtested.

Sources

Word data: ENABLE, wordfreq and Princeton WordNet. Derived word bank and puzzle data are licensed CC BY-SA 4.0. Full credits

Word and puzzle data

Word list: ENABLE (Alan Beale and Mendel Cooper, public domain). Word frequency: wordfreq by Robyn Speer and contributors (CC BY-SA 4.0), which includes SUBTLEX by Marc Brysbaert et al. and OpenSubtitles. Definitions and categories: Princeton WordNet 3.0 (WordNet 3.0 licence, © 2006 Princeton University), as packaged in Open Multilingual Wordnet (omw-en 1.4). Clues for every puzzle answer were hand-written or hand-edited for this game.

The derived word bank, dictionary and puzzle data are distributed under Creative Commons Attribution-ShareAlike 4.0. Changes from the sources: subset to words of 3 to 8 letters, frequency tiers, exclusions, short clues written from the definitions, and generation of 1,000 boards (pack LB4) that grow from 3×3 to 8×8, with unique letter sets and an answer word not repeating within 25 levels.