Add a bone to an armature with custom head and tail positions, name, and optional parent for hierarchical rigging.
Add a bone to an armature.
Args: armature_name: Target armature. bone_name: Name for the bone. head: [x, y, z] bone head position. tail: [x, y, z] bone tail position. parent_bone: Parent bone name (for hierarchy).
| Name | Required | Description | Default |
|---|---|---|---|
| head | No | ||
| tail | No | ||
| bone_name | Yes | ||
| parent_bone | No | ||
| armature_name | Yes |
Changes observed during successful MCP inspections.
v3.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It implies a mutation (adding a bone) but does not disclose potential side effects, failure conditions (e.g., duplicate bone name, missing armature), or whether the operation modifies the scene destructively. It also doesn't mention return values or errors. The description only restates parameter purposes without behavioral context.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, clear sentence followed by a bulleted parameter list. It is front-loaded with the action, and every line serves a purpose. No redundant or filler content. The structure is easy to scan and parse.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple mutation tool with five parameters and no output schema, the description covers the parameters but misses important context: it doesn't state whether the armature must already exist, how the bone is positioned in 3D space, whether parent_bone is optional, or what happens if the bone_name conflicts. It also doesn't explain the default behavior of head and tail when null. These gaps leave room for misuse, so the description is adequate but not complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description is the only source of parameter meaning. It provides a concise explanation for each parameter (e.g., 'head: [x, y, z] bone head position'), adding value beyond the schema's type and title. However, it lacks details like units, coordinate system, or behavior when head/tail are omitted (default null), so it doesn't fully compensate for the schema's lack of descriptions.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states 'Add a bone to an armature' – a specific verb and resource, clearly distinguishing it from siblings like create_armature (which creates the armature) and add_bone_constraint (which adds constraints to bones). No ambiguity about what this tool does.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description gives no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., that the armature must already exist), nor does it cross-reference related tools like create_armature or add_bone_constraint. The user must infer usage from the name and context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.