io.github.Lynn-hh/armguard-mcp

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plan_to_joints

Read-only

Plans a joint-space motion from the current state to target joint positions without moving the robot; validates the trajectory against the safety envelope and returns a plan ID for execution.

Instructions

Plan (do NOT move) a joint-space motion from the current state to joint_positions [rad]. Returns a plan summary validated against the safety envelope; if status is not 'rejected', pass plan_id to execute_plan. Scaling above the policy cap is clamped.

Input Schema

Name	Required	Description
`joint_positions`	Yes	Target joint positions [rad], one per joint in the order ['fr3_joint1', 'fr3_joint2', 'fr3_joint3', 'fr3_joint4', 'fr3_joint5', 'fr3_joint6', 'fr3_joint7']
`velocity_scaling`	No	Fraction of max joint speed (0, 1]
`acceleration_scaling`	No	Fraction of max joint accel (0, 1]

Output Schema

Name	Required	Description
`kind`	Yes
`notes`	No
`status`	Yes	rejected plans can never be executed; needs_approval requires a human to approve
`dry_run`	Yes
`plan_id`	Yes
`duration_s`	Yes
`executable`	Yes
`expires_at`	No	ISO-8601 UTC expiry of the plan handle
`violations`	No
`final_ee_pose`	Yes
`num_waypoints`	Yes
`force_monitoring`	Yes	Whether the backend currently provides an external wrench estimate. Without one the server cannot enforce the contact force limit, and execute_plan refuses to move unless the policy sets force.require_wrench: false
`velocity_scaling`	Yes
`requires_approval`	Yes
`tcp_path_length_m`	Yes
`acceleration_scaling`	Yes
`max_joint_travel_rad`	Yes
`final_joint_positions`	Yes
`start_joint_positions`	Yes
`max_joint_velocity_ratio`	Yes	Peak joint speed as a fraction of the joint limit
`max_joint_acceleration_ratio`	Yes	Peak joint acceleration (estimated from the waypoint timing) as a fraction of the joint limit

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 26, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Adds real context beyond the annotations: the plan is validated against the safety envelope, a plan summary with a status field is returned, and scaling above the policy cap is clamped rather than rejected. The readOnlyHint=true annotation aligns with "do NOT move", so no contradiction. It doesn't say what a 'rejected' status implies or whether plan_ids expire.

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

Conciseness5/5

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

Front-loads the critical constraint "(do NOT move)" and packs purpose, validation, next step, and clamping behavior into two tight sentences with no filler.

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

Completeness5/5

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

Covers what the tool does, what it returns conceptually (plan summary + status), what to do next (plan_id to execute_plan), and edge-case behavior (clamping). With an output schema present, nothing material is left for the description to carry.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3, but the description adds meaning the schema lacks: the clamping behavior when scaling exceeds the policy cap explains what actually happens at the boundary instead of just stating a max. It also reinforces the [rad] unit and current-state origin for joint_positions.

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 ("Plan ... a joint-space motion") and disambiguates from pose/Cartesian planning siblings via "joint-space" plus the explicit "do NOT move" scope limit. An agent can pick it apart from plan_to_pose and plan_cartesian_path without opening any schema.

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

Usage Guidelines4/5

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

Gives a concrete workflow rule: if status is not 'rejected', pass plan_id to execute_plan — clear downstream handoff. It also implies what not to expect (this tool does not move the robot). It stops short of naming plan_to_pose/plan_cartesian_path as alternatives with a stated selection condition.

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