chirp

Game sound effects and music as code. Write a small .cx.js file of tones, noise, envelopes
and patterns; chirp synthesizes WAV/OGG for every sound, chiptune songs that loop seamlessly, and
audio-sprite banks with JSON for Howler.js and Phaser. A live player rebuilds on save and plays
what you just changed.

Built for AI agents (it ships as a Claude Code skill). An agent can't hear, so every build also
writes a waveform + spectrogram preview and chirp info prints levels, clipping and the pitch
over time: the agent reads its sounds the way it reads its code.

Part of a family with vex (vector art, skeletal animation), pxl (pixel art), kiln (low-poly and voxel 3D) and loom (seamless textures and PBR materials). Inspired by
claude-pxl (pixel art), with the same architecture:
sandboxed source files, lazy cached builds, errors with exact locations, and a live viewer.

Showcase

Everything here is synthesized from code in showcase/. No samples, no recordings.

LAST CUP: a soundtrack for the vex noir scene

▶ Watch the scene with sound · ambience OGG ·
source: last_cup.cx.js

Rain on the glass with droplet plinks, a distant city drone and a far-off siren, the faint 15.7 kHz
whine of an old CRT, a tired electric piano in A minor, and the neon sign's buzz, which cuts out on
exactly the video frames where its dying letter flickers off:

LAST CUP (isometric): a 32 s room in sync with a pixel-art loop

▶ Listen (OGG) · source: last_cup_iso.cx.js ·
picture: the isometric scene in pxl

Scored for the pxl isometric cafe, whose animation loops every 1.6 s: the mix is exactly 20 loops.
Rain muffled by the window on the left, the city's sub-drone and a siren that never comes closer,
the CAFE sign's hum (dark on the same frames its F dies), the bar's kick-plate strip and the bulb,
the CRT's flyback whine, the robot's tired fan, a relay that clicks, servos as he lifts and lowers the
cup twice (in sync with the sip in the pixel art), a clink, oil dripping, the hooded sleeper's breathing,
a half-dead espresso machine, and a slow D minor theme. A second 10 s mix, last_cup_iso_3d, follows
the kiln version's clip instead.

Forest Kit: the sounds of the vex platformer pack

▶ Listen to all 22 sounds · bank OGG ·
source: forest_kit.cx.js

Jump, double jump, landing, footsteps (3 takes), coin, gem, heart, potion glugs, key, creaking
chest, hurt, slime, bat flap and screech, a seamless torch-crackle loop, UI sounds, and win and
game-over jingles, packed as one audio sprite with JSON offsets.

▶ Listen to the forest theme · OGG:
a 16-bar AABA chiptune loop. Pulse lead with delayed vibrato, arpeggiated chords and triangle
bass, all built from chord names with a few lines of JS.

coin	jump	chest_open

Quick start

git clone https://github.com/uilianks/chirp && cd chirp
npm install
node bin/chirp.js build examples/basics.cx.js        # -> examples/out/
node bin/chirp.js serve showcase/all.cx.js           # live player on http://127.0.0.1:4330

In the player, ✎ annotate (or a) lets you mark spans of time (and frequency bands) on the
spectrogram, pin notes to moments and send to Claude. The feedback lists the bar and beat for songs
and which layers are loudest in each span, with their source lines, so "check the feedback" is enough.

sfx("coin", { vol: 0.45 },
  tone({ wave: "square", freq: "B5", dur: 0.055, duty: 0.25 }),
  at(0.055, tone({ wave: "square", freq: "E6", dur: 0.18, duty: 0.25 })))
sfx("coin_big", { base: "coin", pitch: -5 })

sfx("explosion", { fx: [crush({ bits: 8 }), drive({ amount: 1.6 })] },
  noise({ color: "brown", dur: 0.5, filter: { type: "lp", from: 4000, to: 150 } }),
  tone({ wave: "sine", freq: 110, to: 35, dur: 0.4 }))

inst("lead", { wave: "square", duty: 0.25, env: [0.004, 0.1, 0.55, 0.07] })
song("theme", { bpm: 140 },
  track("lead", "E5 . G5 . C6 - B5 . | A5 . G5 . E5 - - ."),
  track("kick", "x . . . x . . ."), track("hat", ". x . x . x . x"))

bank("game_sfx", ["coin*", "explosion"])

$ chirp info sounds.cx.js coin
sfx coin: 0.4s  peak -6.8 dBFS  rms -16.79 dBFS  brightness 5196 Hz
pitch: B5 (988Hz -16dB) @0s → E6 (1318Hz -15dB) @0.05s

Features

• Voices: band-limited square (with duty), saw, triangle, sine, two-operator FM (bells, electric
  pianos, brass), white/pink/brown noise, chip sample-and-hold noise, and sample() for recorded WAVs
  (voice, foley, drum hits) repitched by note; ADSR envelopes, pitch slides, arpeggios, vibrato,
  tremolo, sweeping filters.
• Effects: delay (with ping-pong), Freeverb-style reverb, bitcrush, drive, filter sweeps, chorus,
  and a peak limiter for mixes that never clip.
• Music: instruments (voice options, samples or functions), built-in drum kit, tracker-style patterns
  with chords, holds, accents and swing, chord("Am7") / scale("D", "dorian") helpers for harmony.
  Songs loop seamlessly by default and also export as MIDI for a DAW.
• Reuse: variants (base + pitch), play() to layer sounds, at() for timing, JS for everything else.
• Game output: WAV, OGG (--ogg, via ffmpeg), audio-sprite banks + Howler JSON. Silent tails are
  trimmed and loop tails wrap onto the start.
• Agent ears: spectrogram previews, chirp info pitch traces, clipping warnings, located errors.
• Live player: rebuilds on save, auto-plays the edited sound, loops, solos layers.

Agent workflow: SKILL.md · Full API: reference.md

Use as a Claude Code skill

git clone https://github.com/uilianks/chirp ~/.claude/skills/chirp-game-audio
cd ~/.claude/skills/chirp-game-audio && npm install

Requires Node ≥ 22.18. npm run check typechecks and runs the tests.

License

MIT. Portions adapted from claude-pxl
(MIT, © crsolver), via vex.