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assembly_session

Destructive

Build persistent-joint FreeCAD assemblies: ground parts, add components, define mates, solve, verify, and roll back steps so joints survive later moves.

Instructions

Persistent-joint assembly on FreeCAD's Assembly workbench; prefer it over the one-shot assemble when joints must survive later moves.

Workflow: start(ground=part), add_component(part), mate(a, b, joint_type, trim?), solve, verify, complete. Moving a parent part and re-solving moves the children. rollback(to_step) restores placements atomically. A mate ref is {"part": <name>} plus exactly one of face="FaceN", anchor=<name> or point=[x,y,z].

Reference: operation_help("assembly_session").

Input Schema

TableJSON Schema

Name	Required	Default
`a`	No
`b`	No
`name`	No
`part`	No
`trim`	No
`joint`	No
`to_step`	No
`doc_name`	No
`operation`	Yes
`joint_type`	No	fixed
`gap_samples`	No

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv0.7.7Oct 7, 2026

addedInput schema / properties / gap_samples / maximum
```
Added value: +64
```
addedInput schema / properties / gap_samples / minimum
```
Added value: +2
```

changedInput schema / properties / to_step / anyOf

Previous value: -[
-  {
-    "type": "integer"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "maximum": 1000000,
+    "minimum": 0,
+    "type": "integer"
+  },
+  {
+    "type": "null"
+  }
+]

First observedv0.4.0Jul 31, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already flag destructive=true and idempotent=false, but the description adds genuinely non-derivable behavior: parent moves propagate to children on re-solve, rollback(to_step) restores placements atomically, and state persists across calls. It stops short of covering failure modes or required permissions, so a 4 rather than 5.

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

Conciseness4/5

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

Front-loaded with purpose and routing before the workflow and mate-ref syntax. Every line earns its place, though the inline mate-reference sentence is dense and the trailing operation_help pointer deflects detail that could have been stated.

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

Completeness3/5

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

For a stateful 11-parameter tool with 0% schema descriptions, the description covers the workflow spine and rollback semantics but leaves several parameter meanings and the exact operation-to-argument mapping unstated. An output schema exists, so return values need no explanation, and the operation_help reference partly offsets the gaps, but the definition is not fully self-sufficient.

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 coverage is 0%, so the description must carry the parameter burden. It explains the operation vocabulary (start/add_component/mate/solve/verify/complete/rollback), part=ground, to_step, joint_type/trim, and the mate ref shape ({part} plus exactly one of face/anchor/point), but leaves a, b, name, doc_name, and gap_samples undefined. Partial compensation only.

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 ('Persistent-joint assembly on FreeCAD's Assembly workbench') and explicitly positions it against the sibling 'assemble' ('prefer it over the one-shot assemble when joints must survive later moves'). An agent can distinguish it from assemble without opening 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?

Names the alternative explicitly and the condition that selects it (joints must survive later moves), and supplies the ordered workflow (start, add_component, mate, solve, verify, complete). Routing decision is fully determined without inference.

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