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add_assembly_interface

Read-only

Define how two parts connect by specifying joint type, clearance, and optional fastener hardware so assembly validation and clearance checks can run. Enables accurate BOMs and manuals.

Instructions

Add a mating interface between two parts in an assembly.

        Defines how two parts connect (joint type and clearance),
        which is used during validation and clearance checking.  For
        screw/anchor-based joints, ``fastener`` may provide an
        explicit hardware spec so downstream manuals and BOM tools do
        not have to guess from clearance alone.

        Args:
            assembly_json: JSON string of the current assembly state.
            part_a_id: ID of the first part in the interface.
            part_b_id: ID of the second part in the interface.
            joint_type: Type of joint (default ``"clearance_fit"``).
            clearance_mm: Clearance gap in mm (default 0.2).  For
                ``"interference_fit"`` pass a NEGATIVE value (the
                part is intentionally larger than its socket);
                interference geometry is the entire point.
            magnet_polarity_aligned: Only meaningful when
                ``joint_type == "magnetic"``.  ``True`` declares
                the designer has confirmed which poles face each
                other in each magnet pocket; ``None`` means
                unknown.  Downstream tooling refuses to ship a
                hand-wavy "make sure they pull together"
                instruction when polarity is unknown.
            fastener: Optional FastenerSpec as a dict or JSON object
                string.  Supported keys include ``size``, ``family``,
                ``length_mm``, ``length_range_mm``, ``head_type``,
                ``drive_type``, ``surface_type``,
                ``quantity_per_interface``, and ``notes``.

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": {
      "assembly_json": "<assembly_json>",
      "part_a_id": "<part_a_id>",
      "part_b_id": "<part_b_id>"
    },
    "name": "add_assembly_interface"
  }
}

Input Schema

Name	Required	Description
`fastener`	No	Optional FastenerSpec as a dict or JSON object string. Supported keys include ``size``, ``family``, ``length_mm``, ``length_range_mm``, ``head_type``, ``drive_type``, ``surface_type``, ``quantity_per_interface``, and ``notes``.
`part_a_id`	Yes	ID of the first part in the interface.
`part_b_id`	Yes	ID of the second part in the interface.
`joint_type`	No	Type of joint (default ``"clearance_fit"``). Default: "clearance_fit".
`clearance_mm`	No	Clearance gap in mm (default 0.2). For ``"interference_fit"`` pass a NEGATIVE value (the part is intentionally larger than its socket); interference geometry is the entire point. Default: 0.2.
`assembly_json`	Yes	JSON string of the current assembly state.
`magnet_polarity_aligned`	No	Only meaningful when ``joint_type == "magnetic"``. ``True`` declares the designer has confirmed which poles face each other in each magnet pocket; ``None`` means unknown. Downstream tooling refuses to ship a hand-wavy "make sure they pull together" instruction when polarity is unknown.

Schema Changelog

Changes observed during successful MCP inspections.

Changed7 schema fields changedv1.5.1Nov 5, 2026

addedInput schema / properties / assembly_json / description

Added value: +"JSON string of the current assembly state."

changedInput schema / properties / clearance_mm / description

Previous value: -"Default: 0.2."New value: +"Clearance gap in mm (default 0.2).  For ``\"interference_fit\"`` pass a NEGATIVE value (the part is intentionally larger than its socket); interference geometry is the entire point. Default: 0.2."

addedInput schema / properties / fastener / description

Added value: +"Optional FastenerSpec as a dict or JSON object string.  Supported keys include ``size``, ``family``, ``length_mm``, ``length_range_mm``, ``head_type``, ``drive_type``, ``surface_type``, ``quantity_per_interface``, and ``notes``."

changedInput schema / properties / joint_type / description

Previous value: -"Default: \"clearance_fit\"."New value: +"Type of joint (default ``\"clearance_fit\"``). Default: \"clearance_fit\"."

addedInput schema / properties / magnet_polarity_aligned / description

Added value: +"Only meaningful when ``joint_type == \"magnetic\"``.  ``True`` declares the designer has confirmed which poles face each other in each magnet pocket; ``None`` means unknown.  Downstream tooling refuses to ship a hand-wavy \"make sure they pull together\" instruction when polarity is unknown."

addedInput schema / properties / part_a_id / description

Added value: +"ID of the first part in the interface."

addedInput schema / properties / part_b_id / description

Added value: +"ID of the second part in the interface."

Changed8 schema fields changedv1.5.0Oct 23, 2026
- addedInput schema / properties / assembly_json / anyOf
```
Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "additionalProperties": true,
+    "type": "object"
+  }
+]
```
- removedInput schema / properties / assembly_json / type
```
Removed value: -"string"
```
- removedInput schema / properties / clearance_mm / default
```
Removed value: -0.2
```
- addedInput schema / properties / clearance_mm / description
```
Added value: +"Default: 0.2."
```
- removedInput schema / properties / fastener / default
```
Removed value: -null
```
- removedInput schema / properties / joint_type / default
```
Removed value: -"clearance_fit"
```
- addedInput schema / properties / joint_type / description
```
Added value: +"Default: \"clearance_fit\"."
```
- removedInput schema / properties / magnet_polarity_aligned / default
```
Removed value: -null
```
First observedv0.1.0Jul 4, 2026

TDQS

B3/5.0

Behavior1/5

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

The description declares a state-changing operation ('Add a mating interface', defining how parts connect and feeding downstream manuals and BOM tools), while annotations set readOnlyHint=true and destructiveHint=false. This directly contradicts the annotation, so the agent cannot tell whether the call mutates assembly_json or is a pure read.

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?

Purpose and behavioral notes are front-loaded and readable, but the Args section restates the input schema line for line, which is substantial wasted length. Some of that content earns its place (interference-fit sign convention, polarity rationale), yet the duplication drags structure down.

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?

For a 7-parameter mutation with no output schema and no enums, the description covers joint semantics, clearance sign conventions, polarity handling, and the fastener spec keys well enough to call the tool correctly. What it omits is the consequence of the call on assembly state and any error conditions, which matters more given the contradictory readOnlyHint.

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% and the description's Args block reproduces the schema descriptions almost verbatim, adding no meaning beyond what structured fields already provide. The genuinely useful nuance (negative clearance_mm for interference_fit, polarity 'unknown' blocking shipment) appears in both places, so baseline 3 applies.

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

Purpose4/5

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

The description opens with a specific verb and resource ('Add a mating interface between two parts in an assembly') and explains that the interface defines joint type and clearance used during validation and clearance checking, which separates it from part-level siblings like add_assembly_part. It never names a sibling tool or an explicit alternative, so it falls short of full differentiation.

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

Usage Guidelines3/5

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

Usage context is implied rather than stated: the interface is 'used during validation and clearance checking', which tells the agent when the data matters downstream, and conditional guidance exists for fastener (screw/anchor joints) and magnet_polarity_aligned (only when joint_type == 'magnetic'). There is no explicit when-to-use-this-instead-of-X guidance and no prerequisites or exclusions.

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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