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Kiln

by codeofaxel
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python

merge_stl

Combine multiple STL files into one mesh, applying per-file X/Y/Z offsets to position parts relative to each other before export.

Instructions

Merge multiple STL files into a single mesh (supports positional offsets).

Use this when you need to position parts relative to each other.
For simple concatenation without positioning, ``merge_mesh_files`` also works.
Combines triangle data from multiple STL files into one output file.
Optionally translates each part to a specified position before merging.

:param file_paths: JSON array of STL file paths.
:param output_path: Where to write the merged STL.
:param positions: Optional JSON array of {"x", "y", "z"} offsets per file.
:returns: Dict with output_path, total_triangles, bounding_box.

INLINE 3D STAGE: on success this tool opens Kiln's interactive 3D stage — an inline viewer panel the user can orbit, zoom, and turn over — in hosts that render MCP Apps panels (Kiln's hosted connection attaches a browser stage link for hosts that don't). Oversized meshes are decimated automatically for the stage; the PNG preview is the floor, not the whole experience.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "file_paths": "<file_paths>",
      "output_path": "<output_path>"
    },
    "name": "merge_stl"
  }
}

Input Schema

NameRequiredDescriptionDefault
positionsNoOptional JSON array of {"x", "y", "z"} offsets per file. Default: "".
file_pathsYesJSON array of STL file paths.
output_pathYesWhere to write the merged STL.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv1.5.1
    • addedInput schema / properties / file_paths / description
      Added value: +"JSON array of STL file paths."
    • addedInput schema / properties / output_path / description
      Added value: +"Where to write the merged STL."
    • changedInput schema / properties / positions / description
      Previous value: -"Default: \"\"."New value: +"Optional JSON array of {\"x\", \"y\", \"z\"} offsets per file. Default: \"\"."
  2. Changed2 schema fields changedv1.5.0
    • removedInput schema / properties / positions / default
      Removed value: -""
    • addedInput schema / properties / positions / description
      Added value: +"Default: \"\"."
  3. First observedv0.1.0

TDQS

A4.2/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the write-but-not-destructive profile is known. The description adds context annotations don't carry: it writes to a user-supplied output path, optionally translates each part before merging, and on success opens an interactive 3D stage where oversized meshes are auto-decimated. It does not say whether an existing file at output_path is overwritten, which is the main remaining behavioral gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The strongest content (purpose, when-to-use, sibling alternative) is front-loaded in the first two sentences and readable at a glance. However, the ':param' and ':returns' block duplicates the input schema and supplies no new information, and the inline-stage paragraph runs long relative to the one fact it conveys (a viewer panel opens, large meshes are decimated).

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, and the description compensates by naming the return shape (output_path, total_triangles, bounding_box). Combined with the documented offsets parameter and the stage behavior, an agent has nearly everything needed. The only omission is file-overwrite/conflict behavior at output_path for a tool that writes a new artifact.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all three parameters are already documented. The ':param' lines in the description restate the schema text nearly verbatim (JSON array of STL paths, where to write, optional {"x","y","z"} offsets) and add no syntax, ordering, or validation detail beyond it. Baseline 3 applies when the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Merge multiple STL files into a single mesh') plus a distinguishing capability ('supports positional offsets'), and explicitly names the sibling merge_mesh_files as the tool it is not. An agent can separate the two without inspecting either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit when-to-use condition ('when you need to position parts relative to each other') and names the alternative for the other case ('For simple concatenation without positioning, merge_mesh_files also works'). This is the when/when-not/alternative pattern done properly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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