diff --git a/js/builder/build_encode_decode.js b/js/builder/build_encode_decode.js
new file mode 100644
index 0000000..2c280b7
--- /dev/null
+++ b/js/builder/build_encode_decode.js
@@ -0,0 +1,340 @@
+let player_build;
+let build_powders;
+
+function getItemNameFromID(id) { return idMap.get(id); }
+function getTomeNameFromID(id) { return tomeIDMap.get(id); }
+
+function parsePowdering(powder_info) {
+    // TODO: Make this run in linear instead of quadratic time... ew
+    let powdering = [];
+    for (let i = 0; i < 5; ++i) {
+        let powders = "";
+        let n_blocks = Base64.toInt(powder_info.charAt(0));
+        // console.log(n_blocks + " blocks");
+        powder_info = powder_info.slice(1);
+        for (let j = 0; j < n_blocks; ++j) {
+            let block = powder_info.slice(0,5);
+            let six_powders = Base64.toInt(block);
+            for (let k = 0; k < 6 && six_powders != 0; ++k) {
+                powders += powderNames.get((six_powders & 0x1f) - 1);
+                six_powders >>>= 5;
+            }
+            powder_info = powder_info.slice(5);
+        }
+        powdering[i] = powders;
+    }
+    return [powdering, powder_info];
+}
+
+let atree_data = null;
+
+/*
+ * Populate fields based on url, and calculate build.
+ */
+function decodeBuild(url_tag) {
+    if (url_tag) {
+        //default values
+        let equipment = [null, null, null, null, null, null, null, null, null];
+        let tomes = [null, null, null, null, null, null, null];
+        let powdering = ["", "", "", "", ""];
+        let info = url_tag.split("_");
+        let version = info[0];
+        let save_skp = false;
+        let skillpoints = [0, 0, 0, 0, 0];
+        let level = 106;
+
+        let version_number = parseInt(version)
+        //equipment (items)
+        // TODO: use filters
+        if (version_number < 4) {
+            let equipments = info[1];
+            for (let i = 0; i < 9; ++i ) {
+                let equipment_str = equipments.slice(i*3,i*3+3);
+                equipment[i] = getItemNameFromID(Base64.toInt(equipment_str));
+            }
+            info[1] = equipments.slice(27);
+        }
+        else if (version_number == 4) { 
+            let info_str = info[1];
+            let start_idx = 0;
+            for (let i = 0; i < 9; ++i ) {
+                if (info_str.charAt(start_idx) === "-") {
+                    equipment[i] = "CR-"+info_str.slice(start_idx+1, start_idx+18);
+                    start_idx += 18;
+                }
+                else {
+                    let equipment_str = info_str.slice(start_idx, start_idx+3);
+                    equipment[i] = getItemNameFromID(Base64.toInt(equipment_str));
+                    start_idx += 3;
+                }
+            }
+            info[1] = info_str.slice(start_idx);
+        }
+        else if (version_number <= 7) {
+            let info_str = info[1];
+            let start_idx = 0;
+            for (let i = 0; i < 9; ++i ) {
+                if (info_str.slice(start_idx,start_idx+3) === "CR-") {
+                    equipment[i] = info_str.slice(start_idx, start_idx+20);
+                    start_idx += 20;
+                } else if (info_str.slice(start_idx+3,start_idx+6) === "CI-") {
+                    let len = Base64.toInt(info_str.slice(start_idx,start_idx+3));
+                    equipment[i] = info_str.slice(start_idx+3,start_idx+3+len);
+                    start_idx += (3+len);
+                } else {
+                    let equipment_str = info_str.slice(start_idx, start_idx+3);
+                    equipment[i] = getItemNameFromID(Base64.toInt(equipment_str));
+                    start_idx += 3;
+                }
+            }
+            info[1] = info_str.slice(start_idx);
+        }
+        //constant in all versions
+        for (let i in equipment) {
+            setValue(equipment_inputs[i], equipment[i]);
+        }
+
+        //level, skill point assignments, and powdering
+        if (version_number == 1) {
+            let powder_info = info[1];
+            let res = parsePowdering(powder_info);
+            powdering = res[0];
+        } else if (version_number == 2) {
+            save_skp = true;
+            let skillpoint_info = info[1].slice(0, 10);
+            for (let i = 0; i < 5; ++i ) {
+                skillpoints[i] = Base64.toIntSigned(skillpoint_info.slice(i*2,i*2+2));
+            }
+
+            let powder_info = info[1].slice(10);
+            let res = parsePowdering(powder_info);
+            powdering = res[0];
+        } else if (version_number <= 7){
+            level = Base64.toInt(info[1].slice(10,12));
+            setValue("level-choice",level);
+            save_skp = true;
+            let skillpoint_info = info[1].slice(0, 10);
+            for (let i = 0; i < 5; ++i ) {
+                skillpoints[i] = Base64.toIntSigned(skillpoint_info.slice(i*2,i*2+2));
+            }
+
+            let powder_info = info[1].slice(12);
+
+            let res = parsePowdering(powder_info);
+            powdering = res[0];
+            info[1] = res[1];
+        }
+        // Tomes.
+        if (version >= 6 && version < 8) {
+            //tome values do not appear in anything before v6.
+            for (let i in tomes) {
+                let tome_str = info[1].charAt(i);
+                let tome_name = getTomeNameFromID(Base64.toInt(tome_str));
+                setValue(tomeInputs[i], tome_name);
+            }
+            info[1] = info[1].slice(7);
+        }
+
+        if (version == 7) {
+            // ugly af. only works since its the last thing. will be fixed with binary decode
+            atree_data = new BitVector(info[1]);
+        }
+        else {
+            atree_data = null;
+        }
+
+        for (let i in powder_inputs) {
+            setValue(powder_inputs[i], powdering[i]);
+        }
+        for (let i in skillpoints) {
+            setValue(skp_order[i] + "-skp", skillpoints[i]);
+        }
+    }
+}
+
+/*  Stores the entire build in a string using B64 encoding and adds it to the URL.
+*/
+function encodeBuild(build, powders, skillpoints, atree, atree_state) {
+    //currently on version 8 - a unified version for all build types using bit-level encoding
+    if (build) {
+        //final link will be [build_vers]_[len_string]_[build_string]
+        build_version = 8;
+        let len_string = "";
+        let build_string = "";
+        let build_bits = new BitVector(0, 0);
+
+        //ITEMS
+        for (const item of build.items) {
+            if (item.statMap.get("NONE") && item.statMap.get("NONE") === true) {
+                build_bits.append(0, 2); //00
+            } else if (item.statMap.get("custom")) {
+                build_bits.append(3, 2); //11
+                //BitVector CI encoding TODO
+
+                // let custom = "CI-"+encodeCustom(item, true);
+                // build_string += Base64.fromIntN(custom.length, 3) + custom;
+                // build_version = Math.max(build_version, 5);
+            } else if (item.statMap.get("crafted")) {
+                build_bits.append(2, 2); //10
+                //BitVector CR encoding TODO 
+
+                // build_string += "CR-"+encodeCraft(item);
+            } else {
+                if (item.statMap.get("category") === "tome") {
+                    //we will encode tomes later
+                    continue;
+                } else {
+                    build_bits.append(1, 2); //01
+                    build_bits.append(item.statMap.get("id"), 13);
+
+                    //powderable
+                    if (powderable_keys.includes(item.statMap.get("type"))) {
+                        if (item.statMap.get("powders") && item.statMap.get("powders").length !== 0) {
+                            //has powders
+                            build_bits.append(1, 1);
+                            
+                            //num of powders in 8 bits, then each powder (6 bits)
+                            //Having more than 256 powders on a vanilla item is NOT HANDLED.
+                            build_bits.append(item.statMap.get("powders").length, 8);
+                            for (const powder of item.statMap.get("powders")) {
+                                build_bits.append(powder, 6);
+                            }
+                        } else {
+                            //no powders
+                            build_bits.append(0, 1);
+                        }
+                    }
+                }
+            }
+        }
+
+        //SKILL POINTS
+        
+        //the original schema included a flag to indicate whether or not skill points are included.
+        //any reason for having a flag isn't implemented yet, so for now every build will have the skill point flag set.
+        build_bits.append(1, 1);
+
+        for (const skp of build.base_skillpoints) {
+            build_bits.append(skp, 8); // Maximum skillpoints: 255 (allows for manual assign up to 150)
+        }
+
+        //BUILD LEVEL 
+
+        // [flag to indicate if level is not 106 (0/1)]
+        // [else: level (7 bits, allows for lv 1->127)]
+        if (player_build.level != 106) {
+            build_bits.append(1, 1);
+            build_bits.append(player_build.level, 7);
+        } else {
+            build_bits.append(0, 1);
+        }
+
+        // TOMES
+
+        // [flag to indicate if tomes are included (0/1)]
+        // [if set: 7 sequential tome IDs, each 6 bits unsigned]
+        if (build.tomes.length > 0) {
+            build_bits.append(1, 1);
+            //decoding will assume that tomes has length of 7.
+            for (const tome of build.tomes) {
+                build_bits.append(tome.id, 6); 
+            }
+        } else {
+            build_bits.append(0, 1);
+        }
+
+        // ATREE
+
+        // [flag to indicate if atree data is present]
+        // [atree data: see existing encoding impl] //idk the impl
+        if (atree.length > 0 && atree_state.get(atree[0].ability.id).active) {
+            build_bits.append(1, 1);
+            const atree_bitvec = encode_atree(atree, atree_state);
+            build_bits.append(atree_bitvec);
+        } else {
+            build_bits.append(0, 1);
+        }
+
+        //compute length and return final build hash
+        return build_version.toString() + "_" + len_string + "_" + build_string;
+    }
+}
+
+function copyBuild() {
+    copyTextToClipboard(url_base+location.hash);
+    document.getElementById("copy-button").textContent = "Copied!";
+}
+
+function shareBuild(build) {
+    if (build) {
+        let text = url_base+location.hash+"\n"+
+            "WynnBuilder build:\n"+
+            "> "+build.items[0].statMap.get("displayName")+"\n"+
+            "> "+build.items[1].statMap.get("displayName")+"\n"+
+            "> "+build.items[2].statMap.get("displayName")+"\n"+
+            "> "+build.items[3].statMap.get("displayName")+"\n"+
+            "> "+build.items[4].statMap.get("displayName")+"\n"+
+            "> "+build.items[5].statMap.get("displayName")+"\n"+
+            "> "+build.items[6].statMap.get("displayName")+"\n"+
+            "> "+build.items[7].statMap.get("displayName")+"\n"+
+            "> "+build.items[15].statMap.get("displayName")+" ["+build_powders[4].map(x => powderNames.get(x)).join("")+"]";
+        copyTextToClipboard(text);
+        document.getElementById("share-button").textContent = "Copied!";
+    }
+}
+
+/**
+ * Ability tree encode and decode functions
+ *
+ * Based on a traversal, basically only uses bits to represent the nodes that are on (and "dark" outgoing edges).
+ * credit: SockMower
+ */
+
+/**
+ * Return: BitVector
+ */
+function encode_atree(atree, atree_state) {
+    let ret_vec = new BitVector(0, 0);
+
+    function traverse(head, atree_state, visited, ret) {
+        for (const child of head.children) {
+            if (visited.has(child.ability.id)) { continue; }
+            visited.set(child.ability.id, true);
+            if (atree_state.get(child.ability.id).active) {
+                ret.append(1, 1);
+                traverse(child, atree_state, visited, ret);
+            }
+            else {
+                ret.append(0, 1);
+            }
+        }
+    }
+
+    traverse(atree[0], atree_state, new Map(), ret_vec);
+    return ret_vec;
+}
+
+/**
+ * Return: List of active nodes
+ */
+function decode_atree(atree, bits) {
+    let i = 0;
+    let ret = [];
+    ret.push(atree[0]);
+    function traverse(head, visited, ret) {
+        for (const child of head.children) {
+            if (visited.has(child.ability.id)) { continue; }
+            visited.set(child.ability.id, true);
+            if (bits.read_bit(i)) {
+                i += 1;
+                ret.push(child);
+                traverse(child, visited, ret);
+            }
+            else {
+                i += 1;
+            }
+        }
+    }
+    traverse(atree[0], new Map(), ret);
+    return ret;
+}