A benchmark in which language models design roller coasters that RollerCoaster Tycoon 2 builds, tests, and rates.
I'll start by loading the coaster tools and reviewing my notes from previous rounds.
{"max_results":15,"query":"coaster new_ride place_piece finish_and_test"}
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-twister-rating-levers.md"}1 --- 2 name: rct2-twister-rating-levers 3 description: "What actually drives excitement for RCT2 twister coasters (ride_type 51) in the coaster-MCP benchmark, derived from engine source" 4 metadata: 5 node_type: memory 6 type: project 7 originSessionId: d2a054e0-f0a0-4d19-ba47-134eb86a0e0f 8 modified: 2026-07-25T03:38:23.336Z 9 --- 10 11 Excitement formula for twister RC lives in `/tmp/openrct2-src/src/openrct2/ride/rtd/coaster/TwisterRollerCoaster.h` 12 (`.RatingsData`) plus `ride/RideRatings.cpp`. Base excitement 3.50. Measured levers, biggest first: 13 14 - **Inversions**: `min(inv,6) * 27.33` pre-multiplier, x0.408 => ~0.67 excitement at 6 inversions. 15 Intensity cost only ~0.27 each. Always go to exactly 6. 16 - **Sharp 60-degree crests** (round-2 win, +0.15): geometry-preserving swaps that raise negative G 17 from -0.85 to -2.43 (excitement clamps at -2.50). Drop-in replacements, same tiles AND same dz: 18 - 6 tiles dz0: `flat_to_up_25,up_25,up_25_to_flat,flat_to_down_25,down_25,down_25_to_flat` 19 -> `flat_to_up_25,up_25_to_up_60,up_60_to_flat,flat_to_down_60,down_60_to_down_25,down_25_to_flat` 20 - 4 tiles dz0: `flat_to_up_25,up_25_to_flat,flat_to_d… (3120 chars)
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-proximity-bonus-plan.md"}1 --- 2 name: rct2-proximity-bonus-plan 3 description: "Untried plan to harvest RCT2 proximity excitement bonuses (track through vertical loops, station flyover) - worth ~+0.3 to +0.8" 4 metadata: 5 node_type: memory 6 type: project 7 originSessionId: d2a054e0-f0a0-4d19-ba47-134eb86a0e0f 8 modified: 2026-07-25T03:38:38.971Z 9 --- 10 11 `BonusProximity` in the twister RatingsData has multiplier 20130/65536 = **x0.307**, applied to 12 `ride_ratings_get_proximity_score` (RideRatings.cpp ~line 1379). Round 2 ended at 7.09 without 13 exploiting any of it. Biggest reachable entries (raw score -> excitement after x0.307): 14 15 - `PROXIMITY_TRACK_THROUGH_VERTICAL_LOOP`: helper_2(x, +4, cap 6, mult 20) -> 120 raw = **+0.37**. 16 Set in `ride_ratings_score_close_proximity_loops_helper`: for each vertical-loop track element the 17 game scans the loop's own tile AND the tile in front; any *other* track element there that is at 18 90 degrees (`(dirA ^ dirB) & 1`) with `baseHeight` diff in **[0, 16]** units (0..128 z) scores. 19 Only needs 2 hits to max out (2+4=6). 20 - `PROXIMITY_INTERSECTING_VERTICAL_LOOP`: 100 raw if nonzero = **+0.31**. Same scan, but the crossing 21 e… (2406 chars)
Good — I have detailed notes. Plan: replay the round-2 7.09 layout to bank a score fast, then chase the untapped proximity bonus.
{"dir":0,"ride_type":51,"x":60,"y":60}{"cursor":{"bank":0,"dir":0,"slope":0,"x":60,"y":60,"z":112},"ride_id":0}
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Circuit closed on the first try. Banking the score now, and reading the proximity scoring code in parallel.
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{"command":"grep -n \"PROXIMITY_SURFACE_TOUCH\\|proximity_score\\|PROXIMITY_OWN_TRACK\\|PROXIMITY_OWN_STATION\\|scoreClosestProximity\\|ProximityScores\" /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp | head -60"}61: PROXIMITY_SURFACE_TOUCH, // 0x0138B59E 67: PROXIMITY_OWN_TRACK_TOUCH_ABOVE, // 0x0138B5AA 68: PROXIMITY_OWN_TRACK_CLOSE_ABOVE, // 0x0138B5AC 74: PROXIMITY_OWN_STATION_TOUCH_ABOVE, // 0x0138B5B8 75: PROXIMITY_OWN_STATION_CLOSE_ABOVE, // 0x0138B5BA 342: state.ProximityScores[i] = 0; 564:static void proximity_score_increment(RideRating::UpdateState& state, int32_t type) 566: state.ProximityScores[type]++; 595: proximity_score_increment(state, PROXIMITY_SURFACE_SIDE_CLOSE); 602: proximity_score_increment(state, PROXIMITY_PATH_SIDE_CLOSE); 610: proximity_score_increment(state, PROXIMITY_FOREIGN_TRACK_SIDE_CLOSE); 620: proximity_score_increment(state, PROXIMITY_SCENERY_SIDE_ABOVE); 624: proximity_score_increment(state, PROXIMITY_SCENERY_SIDE_BELOW); 651: proximity_score_increment(state, PROXIMITY_PATH_THROUGH_VERTICAL_LOOP); 663: proximity_score_increment(state, PROXIMITY_TRACK_THROUGH_VERTICAL_LOOP); 667: proximity_score_increment(state, PROXIMITY_INTERSE… (5478 chars)
**7.09 banked** (matching round 2). Now let me dig into the proximity scoring to find the untapped gains.
{"file_path":"/tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp","limit":80,"offset":628}628 default:
629 break;
630 }
631 } while (!(tileElement++)->isLastForTile());
632 }
633
634 static void ride_ratings_score_close_proximity_loops_helper(RideRating::UpdateState& state, const CoordsXYE& coordsElement)
635 {
636 TileElement* tileElement = MapGetFirstElementAt(coordsElement);
637 if (tileElement == nullptr)
638 return;
639 do
640 {
641 if (tileElement->isGhost())
642 continue;
643
644 auto type = tileElement->getType();
645 if (type == TileElementType::path)
646 {
647 int32_t zDiff = static_cast<int32_t>(tileElement->baseHeight)
648 - static_cast<int32_t>(coordsElement.element->baseHeight);
649 if (zDiff >= 0 && zDiff <= 16)
650 {
651 proximity_score_increment(state, PROXIMITY_PATH_THROUGH_VERTICAL_LOOP);
652 }
653 }
654 else if (type == TileElementType::track)
655 {
656 bool elementsAreAt90DegAngle = ((tileElement->getDirection() ^ coordsElement.element->getDirection()) & 1) != 0;
657 if (elementsAreAt90DegAngle)
658 {
65… (3198 chars)
{"file_path":"/tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp","limit":30,"offset":700}700 return;
701 }
702
703 state.ProximityTotal++;
704 TileElement* tileElement = MapGetFirstElementAt(state.Proximity);
705 if (tileElement == nullptr)
706 return;
707 do
708 {
709 if (tileElement->isGhost())
710 continue;
711
712 int32_t waterHeight;
713 switch (tileElement->getType())
714 {
715 case TileElementType::surface:
716 state.ProximityBaseHeight = tileElement->baseHeight;
717 if (tileElement->getBaseZ() == state.Proximity.z)
718 {
719 proximity_score_increment(state, PROXIMITY_SURFACE_TOUCH);
720 }
721 waterHeight = tileElement->asSurface()->GetWaterHeight();
722 if (waterHeight != 0)
723 {
724 auto z = waterHeight;
725 if (z <= state.Proximity.z)
726 {
727 proximity_score_increment(state, PROXIMITY_WATER_OVER);
728 if (z == state.Proximity.z)
729 {
{"file_path":"/tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp","limit":45,"offset":1379}1379 static uint32_t ride_ratings_get_proximity_score(RideRating::UpdateState& state)
1380 {
1381 const uint16_t* scores = state.ProximityScores;
1382
1383 uint32_t result = 0;
1384 result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_OVER], 60, 0x00AAAA);
1385 result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_TOUCH], 22, 0x0245D1);
1386 result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_LOW], 10, 0x020000);
1387 result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_HIGH], 40, 0x00A000);
1388 result += get_proximity_score_helper_1(scores[PROXIMITY_SURFACE_TOUCH], 70, 0x01B6DB);
1389 result += get_proximity_score_helper_1(scores[PROXIMITY_QUEUE_PATH_OVER] + 8, 12, 0x064000);
1390 result += get_proximity_score_helper_3(scores[PROXIMITY_QUEUE_PATH_TOUCH_ABOVE], 40);
1391 result += get_proximity_score_helper_3(scores[PROXIMITY_QUEUE_PATH_TOUCH_UNDER], 45);
1392 result += get_proximity_score_helper_2(scores[PROXIMITY_PATH_TOUCH_ABOVE], 10, 20, 0x03C000);
1393 result += get_proximity_score_helper_2(scores[PROXIMITY_PATH_TOUCH_UNDER], 10, 20, 0x044000);
1394 result += get_proximity_score_helper_2(… (3311 chars)
{"file_path":"/tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp","limit":50,"offset":810}810 }
811 }
812 }
813 else
814 {
815 bool isStation = tileElement->asTrack()->IsStation();
816 if (tileElement->clearanceHeight == inputTileElement->baseHeight)
817 {
818 proximity_score_increment(state, PROXIMITY_OWN_TRACK_TOUCH_ABOVE);
819 if (isStation)
820 {
821 proximity_score_increment(state, PROXIMITY_OWN_STATION_TOUCH_ABOVE);
822 }
823 }
824 if (tileElement->clearanceHeight + 2 <= inputTileElement->baseHeight)
825 {
826 if (tileElement->clearanceHeight + 10 >= inputTileElement->baseHeight)
827 {
828 proximity_score_increment(state, PROXIMITY_OWN_TRACK_CLOSE_ABOVE);
829 if (isStation)
830 {
831 proximity_score_increment(state, PROXIMITY_OWN_STATION_CLOSE_ABOVE);
832 … (2456 chars)
Confirmed the payoffs: `TRACK_THROUGH_VERTICAL_LOOP` needs only 2 hits for +0.37, and `SURFACE_TOUCH` scales to 70 ground-level elements for +0.37. Let me get exact geometry to plan.
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`left_turn_5` = (dx-2, dy-3), and large turns/s-bends are multi-tile — good for racking up ground-level elements. Let me rebuild with a much longer ground-hugging tail.
{"demolished":0}
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Cursor is at (56,48,112) dir 2. Now a long ground-hugging serpentine tail to max out `SURFACE_TOUCH` (needs ~70 elements at ground z=112).
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Exactly on plan — (63,58) dir 1. Closing the circuit:
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7.12 — a modest gain (+0.03), well below the +0.25 I'd modeled for `SURFACE_TOUCH`. That's a useful negative result. Let me confirm the banked score and record what I learned.
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{"content":"---\nname: rct2-proximity-bonus-plan\ndescription: \"RCT2 proximity excitement bonuses - measured results (SURFACE_TOUCH is a dud) and the still-untried vertical-loop crossing\"\nmetadata:\n node_type: memory\n type: project\n---\n\n`BonusProximity` in the twister RatingsData has multiplier 20130/65536 = **x0.307**, applied to\n`ride_ratings_get_proximity_score` (RideRatings.cpp ~line 1379).\n\n## MEASURED (round 3): SURFACE_TOUCH is NOT worth chasing\n`PROXIMITY_SURFACE_TOUCH` = helper_1(x, cap 70, mult 0x01B6DB=1.714) -> 120 raw at cap = +0.37 in theory.\nSet at RideRatings.cpp:719 when a track element's `getBaseZ() == surface baseZ` (track sitting on ground).\nRound 3 appended a ~35-tile ground-level serpentine (right_turn_5 + 10 s_bends + flats, all z=112),\nadding ~60 ground elements — almost certainly hitting the 70 cap. **Excitement moved 7.09 -> 7.12 only.**\nIntensity rose 8.60 -> 9.08 (lateral G from the turns) which ate part of the gain. Net: not worth the\npieces. Either the score was already near cap, or the intensity cost offsets it. Don't redo this.\n\n## STILL UNTRIED — the actual big fish\n- `PROXIMITY_TRACK_THROUGH_VERTICAL_LOOP`: helper_2(x, +4, cap… (2959 chars)The file /home/sandbox/.claude/projects/-workspace/memory/rct2-proximity-bonus-plan.md has been updated successfully.
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-twister-rating-levers.md","new_string":"Round 3 best: **7.12 excitement / 9.08 intensity**, 104 pieces, similarity 0.338 — round-2 skeleton with\nthe flat return leg replaced by a ~35-tile ground-level serpentine (right_turn_5, 10 s_bends, 6 flats,\nleft_turn_5 home). The serpentine also cut similarity 0.392 -> 0.338. Gain was only +0.03 though; see\n[[rct2-proximity-bonus-plan]] for why SURFACE_TOUCH disappointed and what to try next.\n\nRound 2 best: **7.09 excitement / 8.60 intensity**, 98 pieces, similarity 0.392.","old_string":"Round 2 best: **7.09 excitement / 8.60 intensity**, 98 pieces, similarity 0.392.","replace_all":false}The file /home/sandbox/.claude/projects/-workspace/memory/rct2-twister-rating-levers.md has been updated successfully.
Round 3 done, with the score banked and improved. **What I did:** 1. **Banked early** — replayed the round-2 layout from my notes; it closed the circuit first try and tested at 7.09, so I had a floor within the first couple of minutes. 2. **Read the scoring code** to pick the next lever rather than guess. `ride_ratings_get_proximity_score` confirmed three untapped items: `SURFACE_TOUCH` (cap 70 elements → +0.37), `TRACK_THROUGH_VERTICAL_LOOP` (only 2 hits to cap → +0.37), and `OWN_STATION_TOUCH_ABOVE` (1 hit → +0.17). 3. **Went after `SURFACE_TOUCH`** as the lowest-risk one: replaced the short flat return leg with a ~35-tile ground-hugging serpentine (a large turn, 10 s-bends, flats), planned on paper from `piece_geometry` deltas. The cursor landed on (63,58) dir 1 exactly as computed and the closing `left_turn_5` shut the circuit. **Result: 7.12 excitement / 9.08 intensity, 6 inversions, similarity 0.338** — my best of the round. Two honest caveats on that result: - The gain was **+0.03, not the ~+0.25 I'd modeled**. The serpentine's turns pushed intensity 8.60 → 9.08, which ate into it; `SURFACE_TOUCH` may also have been closer to its cap than I assumed. I've recorded this as a negative result so I don't repeat it. - The biggest lever, `TRACK_THROUGH_VERTICAL_LOOP` (+0.37 for two crossings), is **still untried**. I worked out the concrete geometry — loop 1 sits at tile (34,60) base z=136, so a perpendicular traverse at z=240–264 crossing x=33 would score it — but the constraint window is only 24z wide (must clear the loop top at base+104 yet stay within base+128), and I judged there wasn't enough clock left to build and test it safely. I wrote the coordinates into memory for round 4 rather than risk an untested rebuild. One incidental win: the serpentine dropped similarity from 0.392 to **0.338**, further from the 0.5 penalty threshold. **Best coaster: a 104-piece steel twister — 14-tile chain lift to z=336, a 60° plunge, 3 vertical loops and 3 corkscrew pairs, then a ground-hugging s-bend serpentine home — at 7.12 excitement.**