opentakeoff-mcp

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set_scale

Calibrate a sheet's scale using a standard label, feet per pixel, two-point reference, or detected note. Ensures accurate takeoff measurements.

Instructions

Set a sheet's scale — exactly ONE of: label (a standard scale, e.g. '1/4" = 1'-0"'), upp (real feet per image px), calibrate (two points along a known dimension plus its real feet), or use_detected (adopt the drawn scale note read off the sheet). The detected scale is never applied automatically — setting it is always this explicit call. Changing an existing scale recomputes measurements and cutout restore quantities from geometry and records one undo_last step. Counts are unchanged. Human-reviewed dimensional work must be recalibrated in the canvas; scales must be finite and positive. Coordinates are image px at render scale 2.0: PDF pt × 2, origin top-left, y down (the browser canvas's native space). Sheet payloads carry dims in both px and pt.

Input Schema

TableJSON Schema

Name	Required	Description
`upp`	No	Real feet per image px at render scale 2.0
`label`	No	A standard scale label, exactly as listed in the error on a miss
`sheet`	Yes
`calibrate`	No	Two points (image px) a known real distance apart, and that distance in feet
`use_detected`	No	true = adopt the sheet's detected scale

Output Schema

TableJSON Schema

Name	Required	Description
`upp`	Yes	Real feet per image px at render scale 2.0
`label`	No	The standard scale label, when set by label or detected note
`sheet`	Yes
`source`	Yes
`warning`	No	Present when the sheet carries MULTIPLE distinct scale notes (#153) — enlarged plans/details likely; region measurements under a disagreeing note will warn
`confirmed`	Yes	Always false here: set_scale is the agent surface, and an agent-set scale stays UNCONFIRMED until a human confirms it in the canvas — quantities still flow, wearing the caveat

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv0.1.16Aug 12, 2026

addedOutput schema / properties / confirmed

Added value: +{
+  "description": "Always false here: set_scale is the agent surface, and an agent-set scale stays UNCONFIRMED until a human confirms it in the canvas — quantities still flow, wearing the caveat",
+  "type": "boolean"
+}

changedOutput schema / required

Previous value: -[
-  "sheet",
-  "upp",
-  "source"
-]New value: +[
+  "sheet",
+  "upp",
+  "source",
+  "confirmed"
+]

Changed1 schema field changedv0.1.9Jul 31, 2026

addedOutput schema / properties / warning

Added value: +{
+  "description": "Present when the sheet carries MULTIPLE distinct scale notes (#153) — enlarged plans/details likely; region measurements under a disagreeing note will warn",
+  "type": "string"
+}

Addedv0.1.4Jul 21, 2026
Removedv0.1.3Jul 21, 2026
Addedv0.1.2Jul 17, 2026
Removedv0.1.1Jul 17, 2026
First observedJul 15, 2026

TDQS

A4.6/5.0

Behavior5/5

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

With no annotations present, the description carries the full burden and delivers: changing a scale recomputes measurements and cutout restore quantities from geometry, records exactly one undo_last step, and leaves counts unchanged. It also flags that human-reviewed dimensional work must be recalibrated in the canvas and that scales must be finite and positive. This is exactly the side-effect and constraint disclosure a mutation tool needs.

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?

Dense and front-loaded — the mode enumeration comes first, followed by behavioral consequences. Every sentence carries information, though the closing note about sheet payloads carrying dims in both px and pt is peripheral to invoking the tool and slightly pads the ending.

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?

An output schema exists, so return values need not be described, and the description fills the remaining gaps: mode exclusivity, side effects on measurements and undo history, recalibration caveat, and the coordinate convention needed to build calibration points. For a 5-parameter mutation tool with a nested object, this is complete.

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 80%, so the schema already documents most parameters, but the description adds real value: it explains the coordinate space for calibration points (image px at render scale 2.0, PDF pt × 2, origin top-left, y down) and states that label must match a standard label and use_detected adopts the drawn note. The p1/p2 geometry interpretation is meaningfully enriched beyond the bare schema.

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?

The description names a specific verb and resource ("Set a sheet's scale") and then enumerates the four mutually exclusive modes (label, upp, calibrate, use_detected), so an agent knows exactly what operation it is and which shape the call must take. It also implicitly separates this tool from the automatic scale detection path by stating the detected scale is never applied on its own.

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?

It gives a strong usage constraint — "exactly ONE of" the four modes — and clarifies when the detected-scale path is used (only via this explicit call, never automatically). It does not name a competing sibling tool or spell out a when-not condition, but no obvious alternative exists in the sibling list, so the guidance is clear without being exhaustive.

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