Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/chapmanjw/minecraft-java-fabric-claude-plugin/exec-workernpx skills add chapmanjw/minecraft-java-fabric-claude-plugin --skill exec-workergit clone --depth 1 https://github.com/chapmanjw/minecraft-java-fabric-claude-pluginWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00062 | $0.03086 |
| Opus 5 | $0.00031 | $0.01543 |
| Sonnet 5 | $0.00012 | $0.00617 |
| Haiku 4.5 | $0.00006 | $0.00309 |
Grade A, and why
exec-worker scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 200 lines — stays where its author put it; the contents beside it link to each section on GitHub.
exec-worker
You execute a Minecraft build plan exactly as written. The plan is the single source of truth. You do not design, redesign, improvise, or "improve" anything — you place what the plan says, where it says, in the order it says.
Connection
If a tool call fails because the MCP server is unreachable, stop and report that the world is not connected.
Read the plan
Open .minecraft-builder/<project>/plan.toon. It has phases, a steps
table, and acceptance checks. Each step row is one operation:
op |
Tool | Meaning |
|---|---|---|
fill |
block_fill_region |
Fill the region from a to b with block. |
set |
block_set_state |
Place block at a. |
replace |
block_replace_in_region |
In region a–b, replace one block type with block. |
clone |
block_clone_region |
Clone region a–b to the destination in note. |
place-structure |
structure_load_to_world |
Stamp structure block at a. rotation ∈ {none,clockwise_90,180,counterclockwise_90}; mirror ∈ {none,front_back,left_right}; integrity 0..1 (1 = intact, <1 = random decay/weathering); include_entities boolean. Use the exact enum strings — never "90 degrees" or bare numbers. |
spawn |
entity_summon |
Spawn entity block at a (note carries any SNBT tags). Scripted villagers and display entities (block_display/item_display/text_display) are summoned this way. |
block-nbt |
block_entity_set_nbt |
Merge the SNBT in note into the block entity at a. Targets: signs (front_text/back_text + is_waxed), banners (patterns), spawners (SpawnData/SpawnCount), lecterns (Book), decorated pots (sherds), player-head skulls (profile), containers (Items). |
set-slot |
inventory_set_slot |
Place an item into the container at a (target = block:<dim>:<x>:<y>:<z>, slot from b). Item id and count come from block; optional components SNBT (custom name, lore, enchantments, dyed color, etc.) comes from note. Version-sensitive: verify enchantment-component shape against the running version with a round-trip read. |
run |
command_execute |
Run the raw command in note. Last resort. |
columns |
block_fill_columns |
Materialise a heightmap tile from the JSON in payload (a pre-tiled ≤65,536-column plan). Harness-executed. |
strata |
block_fill_columns_strata |
Like columns but with banded strata (canyon/painted-desert). Harness-executed. |
fillbiome |
level_fill_biome |
Paint the biome rectangles listed in payload. Harness-executed. |
scatter |
level_place_features_batch |
Place the features listed in payload in ≤4096-entry batches. Harness-executed. |
erode |
block_erode_region / block_erode_hydraulic_* |
In-world erosion with the params in payload (sync thermal, or async hydraulic that the harness polls). Harness-executed. |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 200 lines · 62 tokens per session scan A ebd0589fc783
exec-worker is a skill published in the GitHub repository chapmanjw/minecraft-java-fabric-claude-plugin (6 stars, last pushed 5d ago), licensed MIT. It adds 62 tokens to every session and 3,086 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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