Blender MCP

Blender MCP

Use the connected Blender MCP server as the primary interface for live Blender work. Refer to tools by their logical names; the client may expose a qualified variant.

Route the request

1. Decide whether the request depends on live Blender state.
2. For a conceptual Blender question, answer from reliable knowledge or version-correct documentation without probing the scene.
3. For a live task, confirm that relevant Blender MCP tools are available. If they are absent, report that Blender MCP is not installed or enabled in this client; do not silently switch to GUI automation.
4. Call list_blender_instances before inspecting scene state. When one instance is ready, select it; when several are ready, require an explicit instance_id or an exact unique match on visible file/scene metadata. Never choose by port, registry order, foreground window, or recency.
5. Claiming is automatic: the first command of any kind, read or write, claims the single available instance. When several are registered, no command runs until one is named, so select the instance up front rather than after a multiple_instances_require_selection error. Respect manual and claimed_by_other_client; do not bypass a human-reserved Blender window.
6. Start with the smallest read-only inspection that can identify the target and constraints.
7. Prefer, in order:
   • a dedicated structured tool;
   • a runtime schema plus a validated transactional node patch;
   • a small, auditable execute_blender_code call only for the exact primitive the structured surface cannot express.

Treat execute_blender_code as a capability-gap fallback, not a shortcut. In node workflows, do not use arbitrary Python for nodes, interfaces, links, properties, defaults, node-group creation, or Geometry Nodes modifier setup when structured tools can express them. If one primitive still requires Python, isolate that primitive in the smallest call possible, then return immediately to structured export, validation, patching, and readback. Use Python for an entire graph only when the structured surface genuinely cannot express the graph and the missing primitive cannot be isolated; state that limitation before execution.

Do not call every status or inspection tool preemptively. Let the requested outcome determine what evidence is necessary.

Inspect before changing

• Use get_scene_info only when broad scene context is necessary.
• Use get_object_info when the target object is already known.
• Use audit_external_dependencies, inspect_evaluated_mesh, and get_simulation_status instead of diagnostic Python when they answer the question.
• Use node-tree indexes and targeted exports instead of loading a large graph. Read graphs through the default view=auto, which selects the compact slim view; escalate to operations, semantic, or all only for an identified missing fact, since each step roughly doubles context for less information.
• When the user means the visible, current, or selected nodes, call get_node_editor_context; it reports active_node and selected_nodes as exact stable names. Continue automatically only for UNIQUE_EDITOR or PINNED_EDITOR. For MULTIPLE_EDITORS require an explicit choice, and refresh after STALE_CONTEXT; never infer a Node Editor from focus, window order, or recency.
• When a request points at a node by role and no index or query resolves it to one candidate, ask the user to select it in the Node Editor rather than guessing through several rounds of names.
• Use get_runtime_automation_context before version-sensitive Blender Python.
• Resolve version-correct official Blender documentation with get_blender_documentation_context, search_blender_docs, and get_blender_doc_page when an API or feature contract is uncertain.
• Treat returned revisions, editability, owner identity, exact names, and runtime schemas as authoritative.

Apply changes safely

• Preserve the user's current project and unrelated datablocks.
• Validate a node patch before applying it. Keep transactional backups unless the user explicitly prefers otherwise.
• Prefer modify_verify_save when the task benefits from candidate-count assertions and the user has stated a save policy; its default remains unsaved.
• Read back the affected object or targeted subgraph after mutation.
• When creating or formatting nodes, read the reference layout style linked from references/node-workflows.md before placing nodes. Use named stage frames, a left-to-right main path, and local parameter inputs.
• Encapsulate functional modules as subgroups with an explicit interface. Use Frames for processing steps inside a tree; do not turn every step into a subgroup or substitute a Frame for module encapsulation.
• Every non-Frame node in a generated or reformatted tree must have a NodeFrame parent, including Group Input, Group Output, Reroute, constants, and auxiliary nodes. Root frames may be unparented. Check each generated nested tree too.
• Each Frame must contain 4-19 direct child nodes; a nested Frame counts as one child of its parent and must satisfy the same rule itself. Group by meaningful stages, merge tiny steps, and nest complex stages. Do not add filler nodes or decorative frames to meet the count. Use the frame audit linked from references/node-workflows.md.
• Enforce the six strict formatting rules in Strict layout constraints: no overlap or touching between unrelated boxes; every link strictly rightward; exactly one visible used output and one outgoing link per Group Input; Group Inputs within 250 canvas units of their targets and aligned to the receiving sockets; ordered fan-in; compact vertical spacing between stacked neighbors (target 20-40 canvas units edge-to-edge, maximum 60). These are completion requirements, not preferences. Do not relax them for related parameters, local fan-out, uniform oversized rows, or a passing tool result. Never rename built-in nodes to explain their role; use Frame labels.
• Within each processing step's Frame, minimize total internal wire length among layouts satisfying every constraint. Compare legal node orders, columns, and compact placement; do not accept the first valid planner result as the shortest arrangement. Optimize nested steps from the inside out. Preserve semantic membership, computation, and socket order; shorter wires never justify violating a hard rule. See Shortest wiring within each step.
• Run the layout post pass after changes to nodes, links, parenting, widths, socket visibility, or other settings that affect the displayed layout. Require both complete frame membership and readable placement; patch valid=true alone does not verify layout (references/node-workflows.md, "Layout post pass").
• Prefer inspect_node_layout for measured canvas bounds and audit_node_layout for membership, 4-19 counts, containment, overlaps, and wire-order diagnostics. After semantic membership is correct, use plan_node_layout with an explicit main_path to generate a candidate patch, then validate/apply through the tree's existing transaction tools. Reinspect after redraw; predicted/cached dimensions and audit valid=true do not prove visual acceptance. These tools operate on one complete tree, so repeat for authored subgroups and do not use the whole-tree planner for an unrelated local edit.
• Before sending the final response for any live Blender task, call release_blender_instance if this MCP process selected or claimed an instance. Release after read-only work as well as mutation, and also before failure or early-stop handoffs, since a claim taken to read still holds the lock until it is released or expires. If release cannot reach Blender, report that the lease will expire as a fallback. The viewport border marks the instance as AI-occupied for the life of the claim, and a Node Editor joins it once the AI writes that kind of tree; neither is an input lock.
• Use get_viewport_screenshot only when appearance or spatial composition materially affects success. A screenshot is not a substitute for structured verification.
• Do not save, overwrite, or change the path of a .blend file unless the user asked for that outcome.
• Do not begin a provider download, paid generation job, or destructive cleanup unless the request already authorizes it or the user confirms it.
• When arbitrary Python is necessary, confine it to the unsupported primitive, avoid global context assumptions, return compact evidence, and resume the structured workflow immediately afterward.

Handle failures

• Stop after no_registered_instances or a clear disconnected response. Tell the user to open Blender and enable or start the Blender MCP add-on; endpoint allocation and registration are automatic.
• On multiple_instances_require_selection, show bounded file/scene summaries and ask which instance to use. Never probe windows through client-specific computer control to guess.
• On instance_manual or instance_claimed_by_other_client, preserve human control and ask the user to enable or release that Blender instance.
• On file_session_changed or instance_changed, discard the stale target, list instances again, and require a fresh claim before mutation.
• When Blender reports a missing node type, socket, property, or edit capability, inspect the live schema or documentation once. If no equivalent exists, report the limitation instead of guessing.
• Do not bypass linked-library or read-only restrictions with arbitrary Python.
• On validation failure, correct the patch from diagnostics and revalidate before any application attempt.
• On a partial or uncertain result, report what changed, what did not, and the safest recovery action.

Load focused guidance

• Read references/node-workflows.md for Geometry, Shader, or Compositor node work.
• Read references/asset-workflows.md for bundled node assets, PolyHaven, Sketchfab, Hyper3D, or Hunyuan3D.
• Read references/render-workflows.md when visual output, render configuration, or viewport verification is part of acceptance.
• Read references/recovery.md after transport, validation, transaction, or arbitrary-code failures.

Report completion

Summarize the target, the mutation performed, verification evidence, release status, and any retained backup or unsaved state. State explicitly when the Blender file has not been saved.