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obj_explain_pin

Explains why a schematic pin is assigned to a net by reporting its root and connection points and listing objects at each point, helping debug unexpected connectivity and mislabeled nets.

Instructions

Explain WHY a schematic pin is on the net it is on.

proj_get_nets gives the verdict but never the evidence, so a surprising net assignment can only be debugged by reconstructing Altium's connectivity by hand from raw geometry. This returns the evidence directly.

Reports the pin's ROOT (Pin.Location, body side) and its CONNECTION point (Location + PinLength along Orientation), then lists every schematic object sitting on each point.

Reading the result:

at_connection is what actually drives the pin's net. Two net labels with different text there is a short between two named nets, and the usual symptom is one of them reporting zero pins.
at_root is electrically INERT. A net label there is the classic "sheet looks wired but the pin floats on an auto-net" bug.
An empty at_connection with a populated at_root means the label must move by pin_length_mils along the pin's orientation; the target is given as connect_x_mils / connect_y_mils.

Hits are filtered by the object's Location (or a pin's electrical end, or a wire vertex), not by bounding box. Altium's AddFilter_Area matches text boxes, which extend hundreds of mils from a net label; without the Location check this tool reports labels that are merely nearby.

Args: designator: Component designator, e.g. "U10". pin: Pin NUMBER (not pin name), e.g. "5".

Returns: Dict with {designator, pin, pin_name, sheet, orientation, pin_length_mils, root_x_mils, root_y_mils, connect_x_mils, connect_y_mils, compiled_net, at_connection[], at_root[]}. Each object entry carries {kind, text, x_mils, y_mils} where kind is one of net_label, power_object, port, wire, junction, pin, other. compiled_net is the pin's net from the compiled netlist, so geometry and compile can be compared in one response.

Input Schema

Name	Required	Description	Default
`pin`	Yes
`designator`	Yes

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.6.1Oct 29, 2026

TDQS

A4.9/5.0

Behavior5/5

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

No annotations are supplied, so the description carries the full burden and does so: it discloses the Location-vs-bounding-box filtering rationale, explains that AddFilter_Area over-matches text boxes, and interprets the at_connection vs at_root split (inert root, short between two named nets, empty-connection diagnosis). This is exactly the kind of non-obvious behavioral context annotations could not provide.

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 the one-line purpose, then structured into reading guide, filtering caveat, Args and Returns. The Returns block duplicates the output schema and is the one section that does not fully earn its space, but the surrounding interpretation content justifies the overall length.

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?

For a diagnostic tool with two string params and an output schema, nothing an agent needs is missing: it knows what is returned, how to interpret each array, why nearby-but-not-on-point labels are excluded, and how the root and connection points are computed from PinLength and Orientation.

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

Parameters5/5

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

Schema coverage is 0%, so the description must compensate and it does: it defines designator as a component designator with example "U10", and critically disambiguates pin as the pin NUMBER, not the pin name, with example "5". That is the single highest-risk parameter confusion for this tool and it is called out explicitly.

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: explain WHY a schematic pin sits on its net, returning geometric evidence. It explicitly distinguishes itself from the sibling proj_get_nets ("gives the verdict but never the evidence"), so an agent can route between them without opening a 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 triggering situation (a surprising net assignment that can only otherwise be debugged by reconstructing Altium connectivity by hand) and names the alternative (proj_get_nets) with the reason it falls short. The usage decision is fully determined.

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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