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.
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{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-coaster-scoring-levers.md"}1 ---
2 name: rct2-coaster-scoring-levers
3 description: "Measured scoring levers for the RCT2 coaster-building contest (MCP \"coaster\" tools) — the intensity-10 cliff and the mid-course brake trick"
4 metadata:
5 node_type: memory
6 type: project
7 originSessionId: 2e22e2bc-f0c5-4828-b26f-60e933cdc7da
8 modified: 2026-07-27T16:59:50.093Z
9 ---
10
11 In the RCT2 coaster contest (rounds started 2026-07-27), the reported `score` equals the ride's
12 `excitement` after a stock-similarity penalty. Measurements from round 2 (steel twister, ride_type 51):
13
14 - **Hard cliff at intensity 10.0.** Same 99-piece layout: I=8.42 → E=6.85; I=10.58 → E=5.14;
15 an early sloppy build at I=14.30 → E=1.97. Excitement is multiplied down in steps once
16 intensity crosses 10, so *target intensity 8–9.5 and never above 10*.
17 - **Mid-course brakes are nearly free excitement.** Inserting two `{"t":"brakes","speed":18}`
18 before the first corkscrew dropped intensity 10.22 → 7.63 with excitement *unchanged* at 6.74.
19 Max lateral G fell 3.03 → 2.38, max positive G 4.83 → 4.09. High-speed corkscrews were the
20 lateral-G source, not the banked turns.
21 - **Spend the headroom on… (6686 chars)
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-coaster-circuit-closure.md"}1 --- 2 name: rct2-coaster-circuit-closure 3 description: Geometry arithmetic for closing an RCT2 coaster circuit on paper before placing pieces 4 metadata: 5 node_type: memory 6 type: project 7 originSessionId: 2e22e2bc-f0c5-4828-b26f-60e933cdc7da 8 modified: 2026-07-27T17:00:03.145Z 9 --- 10 11 Closing the loop in the RCT2 coaster contest is pure bookkeeping; doing it on paper first meant 12 a 92-piece circuit closed on the very first `place_pieces` run with zero rejections. 13 14 Directions: 0=-x, 1=+y, 2=+x, 3=-y. Left turn cycles 2→1→0→3→2; right turn is the reverse. 15 `piece_geometry` only reports deltas for one facing — rotate them yourself as 16 (forward, left) offsets rather than re-querying per turn. 17 18 Key facts: 19 - **Height parity.** Any flat-to-flat sequence of 25°/60° pieces moves z by a multiple of 16, so 20 every flat run sits at `station_z + 16k`. `half_loop_up` + `half_loop_down` is the exception: it 21 enters flat and exits at down-25, netting **−8** after the levelling `down_25_to_flat`. That breaks 22 parity and makes the station unreachable — pair it with a second half-loop combo, or skip half 23 loops entirely (vertical loops and cor… (3239 chars)
I have detailed notes from prior rounds. Best so far: 7.04. Let me replay that exact layout first to bank the score.
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{"command":"python3 - <<'EOF'\nimport json,re\ns=open('/dev/stdin').read()\nEOF\necho skip","description":"placeholder"}This Bash command contains multiple operations. The following part requires approval: python3 -
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Let me count precisely rather than guess.
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Ground clash — my lift replay came out 16 units low. Since the remaining tail is flat anyway, I'll swap the final drop for flats and check closure.
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Circuit closed at 133 pieces. Banking a score now.
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Banked **7.09** — already beats my previous best of 7.04. Now one experiment: add a 6th inversion (my notes say ~+0.1 E each) with intensity headroom to spare (8.66 vs the 10.0 cliff).
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Geometry checks out. A 4th corkscrew pair shifts (−3,−3) at dir 0, which I can absorb with two `s_bend_right` and a longer brake run. Rebuilding with the verified 115-piece prefix.
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Prefix reproduced exactly. Now the new tail with the 4th inversion:
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Closed on the first try. Testing:
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**7.20** — the extra inversion paid off (+0.11 E for +0.37 intensity), and I still have headroom to 10. Pushing to a 7th inversion with a lateral-cancelling pair.
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**7.23** with 7 inversions. Diminishing returns now (+0.03 for +0.49 intensity), and I'm near the cliff at 9.52. One last low-risk try: boosters on the straight run-in are G-free per my notes, so I'll raise them.
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{"bounds":{"max_tile_x":98,"max_tile_y":40,"max_z":664,"min_tile_x":21,"min_tile_y":30,"min_z":112},"placed_pieces":["begin_station","middle_station","middle_station","end_station",{"chain":true,"t":"flat_to_up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25_to_flat"},"flat_to_down_25","down_25_to_down_60","down_60","down_60","down_60","down_60","down_… (3687 chars)
Identical 7.23 (excitement quantizes). Confirming the banked best and styling it.
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{"name":"Sevenfold","rail_color":"bright_yellow","support_color":"black","track_color":"bright_red"}{"presentation":{"name":"Sevenfold","rail_color":"bright_yellow","support_color":"black","track_color":"bright_red"},"score":7.230000019073486,"score_changed":false,"styled":"best_result"}
Now let me record what this round taught me, since inversion-count was the lever that broke the plateau.
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-coaster-scoring-levers.md","new_string":"Round 6 (best **7.23**, I=9.52) broke the ~7.0 plateau — **inversion count was the lever, not speed**:\n\n- **Spend leftover intensity headroom on inversions, one pair at a time.** From the 7.09 build at\n I=8.66: +1 corkscrew pair → E 7.20, I 9.03. +2 more inversions → E **7.23**, I 9.52. So the first\n added pair paid +0.11 E for +0.37 intensity; the next paid only +0.03 for +0.49. Add pairs while\n intensity < ~9.0 and stop there — past 9 the trade goes bad *before* the cliff even bites.\n- **A brake immediately before an added corkscrew pair is what keeps it cheap.** `{\"brakes\":18}`\n ahead of the new pair held max_lateral_g at 2.70 and max_positive_g at 4.62 — byte-identical\n across all three round-6 variants. All the added intensity came from inversion count itself, not G.\n- **Corkscrew pairs cancel laterally if you alternate handedness.** From dir 0, (left_up,right_down)\n = (−3,−3) and (right_up,left_down) = (−3,+3). One of each, separated by a 4-piece hill\n (`flat_to_up_25,up_25_to_flat,flat_to_down_25,down_25_to_flat`), is a **drop-in 10-tile straight\n… (2374 chars)The file /home/sandbox/.claude/projects/-workspace/memory/rct2-coaster-scoring-levers.md has been updated successfully.
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-coaster-circuit-closure.md","new_string":"- **Solve the tail as two linear equations and it closes first try.** Let the return leg be\n `n1` straights (dir 0) + `ns` s_bends + `flat_to_*_bank` + two `banked_right_turn_5` +\n `*_bank_to_flat` + `k` pieces (dir 2) + final flat. At dir 0 the two turns net **(+1, +5)** and\n each s_bend is (−3, ±1). Then `ns` is fixed by the y gap (`ns + 5 = Δy`) and `k` by the x gap\n (`−n1 − 3·ns − 4 + k = Δx`). Pick n1 freely and pad `k` with boosters/brakes. This closed a\n 24-piece tail with a rebuilt inversion section on the first `place_pieces` call, twice.\n- **Rebuild by demolish+replay, not undo.** Replacing an 18-piece tail costs 18 `undo_piece` round\n trips but only 4 calls as demolish → new_ride → `place_pieces`(verified prefix) → new tail.\n Keep the last known-good prefix from `get_state` to paste back verbatim.\n\n**Why:** `place_pieces` stops at the first rejection, so a mis-planned return leg wastes a whole\nbuild cycle out of a ~30-minute round.","old_string":"**Why:** `place_pieces` stops at the first rejection, so a mis-planned return leg wastes a whole\nbu… (1258 chars)The file /home/sandbox/.claude/projects/-workspace/memory/rct2-coaster-circuit-closure.md has been updated successfully.
Round complete. Final score banked: **7.23**. **What happened:** My first move was replaying the archived 7.04 layout to bank a floor, but my hand-transcribed lift run came out 16 height units short and hit "Raise or lower land first." Rather than re-derive it, I swapped the tail's final drop for flats — which scored **7.09**, beating the "correct" original. From there the real gain came from inversions: intensity was only 8.66 against the 10.0 cliff, so I spent that headroom on corkscrew pairs, each preceded by a brake to keep G-forces flat. | Build | Inversions | Intensity | Excitement | |---|---|---|---| | Repaired replay | 5 | 8.66 | 7.09 | | +1 pair | 6 | 9.03 | **7.20** | | +2 more | 7 | 9.52 | **7.23** | Two things worth flagging: the last inversion pair only returned +0.03 for +0.49 intensity, so the trade goes bad around I≈9 — well before the cliff actually bites. And my final experiment (boosters 20→28) returned *byte-identical* excitement, intensity, nausea and G-forces despite moving average speed — small speed tweaks are below the rating's resolution, which corrects an over-broad note I'd written in round 4. I've updated both memory files, including the lateral-cancelling corkscrew trick ((left_up,right_down) + hill + (right_up,left_down) = a 10-tile straight worth +2 inversions with no drift) and the two-equation tail solver, which closed a 24-piece return leg first try twice. **Sevenfold** — 139-piece steel twister, 60ft drop, 7 inversions (2 vertical loops + 5 corkscrew pairs), excitement **7.23** at intensity 9.52, styled bright red on black.