Canvs

Update elements on the board

update_elements

Destructive

Update elements on a canvas. Requires room_id from a previous Canvs tool result. Pass elements array with id and fields to update. IMPORTANT: in each update object ONLY id is required; all other fields are optional patch fields. Include ONLY elements that need changes; elements omitted from the request remain unchanged on the board. Prefer this tool for SMALL edits to existing diagrams (rename/move/restyle a few elements), typically after query_elements.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`room_id`	Yes	Room ID from a previous Canvs tool result. If you only have a URL, extract it from https://[host]/?room=[room_id] or https://[host]/gdrive?id=[room_id].
`elements`	Yes	Array of element updates (each must have id)

Output Schema

TableJSON Schema

Name	Required	Description
`url`	Yes	Canvas room URL
`isNew`	Yes	Whether a new canvas was created
`room_id`	No	Canvas room ID
`appState`	Yes	Canvas app state (viewBackgroundColor, etc.)
`elements`	Yes	All elements currently on the canvas
`collabUrl`	Yes	Collaboration server URL for Socket.IO

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

Changed1 schema field changedJun 7, 2026

changedInput schema / properties / elements / items / properties / text / description

Previous value: -"New text content (for text elements or arrow labels)"New value: +"New text content. For text elements and rectangle/ellipse/diamond shape labels, Supports the rich-text plugin HTML subset: <b>/<strong>, <i>/<em>, <u>, <br>, <div>/<p>, <ul>/<ol>/<li>, <a href>, <font color>, and <span style=\"color, background/background-color, font-size, font-family\">. Use textAlign for left/center/right alignment; avoid unsupported HTML/CSS. Shape text updates the bound label."

Changed4 schema fields changedJun 2, 2026

addedInput schema / properties / room_id

Added value: +{
+  "description": "Room ID from a previous Canvs tool result. If you only have a URL, extract it from https://[host]/?room=[room_id] or https://[host]/gdrive?id=[room_id].",
+  "type": "string"
+}

removedInput schema / properties / room_url

Removed value: -{
-  "description": "Canvas URL from create_canvas (e.g. https://canvs.io/?room=XXXX) or a Google Drive board URL (e.g. https://canvs.io/gdrive?id=FILE_ID)",
-  "type": "string"
-}

changedInput schema / required

Previous value: -[
-  "room_url",
-  "elements"
-]New value: +[
+  "room_id",
+  "elements"
+]

addedOutput schema / properties / room_id

Added value: +{
+  "description": "Canvas room ID",
+  "type": "string"
+}

Changed13 schema fields changedMay 24, 2026

addedInput schema / properties / elements / items / description

Added value: +"Patch object: only id is required. Include only the fields you want to change."

changedInput schema / properties / elements / items / properties / backgroundColor / description
```
Previous value: -"New fill color"New value: +"New fill color (hex or 'transparent')"
```

changedInput schema / properties / elements / items / properties / fillStyle / description

Previous value: -"New fill style"New value: +"New fill style (solid, hachure, cross-hatch)"

changedInput schema / properties / elements / items / properties / fontSize / description
```
Previous value: -"New font size"New value: +"New font size (for text elements)"
```

changedInput schema / properties / elements / items / properties / id / description

Previous value: -"Element ID to update"New value: +"ID of the element to update (required)"

addedInput schema / properties / elements / items / properties / locked

Added value: +{
+  "description": "Lock/unlock the element",
+  "type": "boolean"
+}

changedInput schema / properties / elements / items / properties / opacity / description
```
Previous value: -"New opacity"New value: +"New opacity (0-100)"
```

changedInput schema / properties / elements / items / properties / points / description

Previous value: -"New points array"New value: +"New points array (for arrow/line/freedraw elements)"

changedInput schema / properties / elements / items / properties / roughness / description

Previous value: -"New roughness"New value: +"New roughness (0=architect, 1=artist, 2=cartoonist)"

changedInput schema / properties / elements / items / properties / strokeColor / description
```
Previous value: -"New stroke color"New value: +"New stroke color (hex)"
```

changedInput schema / properties / elements / items / properties / text / description

Previous value: -"New text content"New value: +"New text content (for text elements or arrow labels)"

changedInput schema / properties / elements / items / properties / type / description

Previous value: -"New element type (e.g. rectangle, ellipse, diamond, arrow, line, freedraw, text, image)"New value: +"New element type"

addedInput schema / properties / elements / items / properties / type / enum

Added value: +[
+  "rectangle",
+  "ellipse",
+  "diamond",
+  "arrow",
+  "line",
+  "freedraw",
+  "text",
+  "image"
+]

Changed7 schema fields changedMay 23, 2026

addedOutput schema / properties / appState / additionalProperties
```
Added value: +true
```

changedOutput schema / properties / appState / description

Previous value: -"Current app state (viewBackgroundColor, etc.)"New value: +"Canvas app state (viewBackgroundColor, etc.)"

addedOutput schema / properties / appState / properties

Added value: +{
+  "viewBackgroundColor": {
+    "type": "string"
+  }
+}

changedOutput schema / properties / elements / description

Previous value: -"Current scene elements for inline SVG rendering"New value: +"All elements currently on the canvas"

addedOutput schema / properties / elements / items

Added value: +{
+  "additionalProperties": true,
+  "type": "object"
+}

removedOutput schema / properties / pendingMermaid

Removed value: -{
-  "description": "Mermaid definition to be rendered client-side",
-  "type": "object"
-}

addedOutput schema / required

Added value: +[
+  "url",
+  "isNew",
+  "collabUrl",
+  "elements",
+  "appState"
+]

Changed3 schema fields changedMay 23, 2026

removedInput schema / properties / elements / items / properties / locked

Removed value: -{
-  "description": "Lock/unlock element",
-  "type": "boolean"
-}

changedInput schema / properties / elements / items / properties / type / description

Previous value: -"New element type"New value: +"New element type (e.g. rectangle, ellipse, diamond, arrow, line, freedraw, text, image)"

removedInput schema / properties / elements / items / properties / type / enum

Removed value: -[
-  "rectangle",
-  "ellipse",
-  "diamond",
-  "arrow",
-  "line",
-  "freedraw",
-  "text",
-  "image"
-]

Changed1 schema field changedApr 26, 2026
- changedInput schema / properties / elements / items / properties / fontFamily / description
```
Previous value: -"New font family"New value: +"New font family (5=Excalifont, 6=Nunito, 7=Lilita One, 8=Comic Shanns)"
```

Changed5 schema fields changedApr 19, 2026

changedInput schema / properties / room_url / description

Previous value: -"Room URL (from create_canvas) or room ID to operate on"New value: +"Canvas URL from create_canvas (e.g. https://canvs.io/?room=XXXX) or a Google Drive board URL (e.g. https://canvs.io/gdrive?id=FILE_ID)"

addedOutput schema / properties / appState

Added value: +{
+  "description": "Current app state (viewBackgroundColor, etc.)",
+  "type": "object"
+}

addedOutput schema / properties / collabUrl

Added value: +{
+  "description": "Collaboration server URL for Socket.IO",
+  "type": "string"
+}

addedOutput schema / properties / elements

Added value: +{
+  "description": "Current scene elements for inline SVG rendering",
+  "type": "array"
+}

addedOutput schema / properties / pendingMermaid

Added value: +{
+  "description": "Mermaid definition to be rendered client-side",
+  "type": "object"
+}

First observedFeb 12, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already indicate this is a destructive/mutating operation (readOnlyHint=false, destructiveHint=true). The description adds critical patch semantics: 'only id is required; all other fields are optional patch fields' and 'elements omitted from the request remain unchanged.' These go beyond the annotations and clarify exactly how the mutation behaves.

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?

The description is compact — five sentences, with key information front-loaded. The critical 'IMPORTANT' caveat is highlighted, and every sentence adds value (purpose, prerequisite, input format, patch behavior, usage context). No fluff or redundancy.

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

Completeness4/5

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

Given the tool's moderate complexity (2 outer params, nested elements objects), the description covers the essential workflow: requires room_id from a previous Canvs result, passes a patch array, and is preferred for small edits after query_elements. It omits failure behavior but is otherwise complete for practical use, especially since an output schema exists.

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

Parameters3/5

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

Schema has 100% coverage, so the baseline is 3. The description reinforces the patch nature of 'elements' and emphasizes that fields are optional, but the schema already describes each property and the items-level note 'only id is required.' No additional meaning beyond the schema is added.

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 opens with 'Update elements on a canvas,' using a specific verb and resource. It clearly distinguishes from siblings by emphasizing 'existing diagrams' and 'small edits' (rename/move/restyle), contrasting with add_elements and delete_elements. This makes the tool's purpose unambiguous.

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?

Provides explicit when-to-use guidance: 'Prefer this tool for SMALL edits to existing diagrams... typically after query_elements.' It also requires room_id from a previous result, covering prerequisites. It stakes a clear position among siblings, though it doesn't explicitly name build/delete alternatives.

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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TDQS

A4.4/5.0

Disambiguation5/5

Each tool has a clear, distinct purpose: add_elements for manual creation, add_elements_from_mermaid for Mermaid-based creation, delete/query/update for lifecycle operations, and get_guide for workflow guidance. The overlap between the two creation tools is explicitly resolved in descriptions, leaving no ambiguity.

Naming Consistency5/5

All tool names follow a consistent verb_noun pattern: add_elements, add_elements_from_mermaid, delete_elements, get_guide, query_elements, update_elements. The modifier 'from_mermaid' extends the base pattern without breaking consistency, and all verbs are clear (add, delete, get, query, update).

Tool Count5/5

With 6 tools, the set is well-scoped for a canvas/diagram server, covering creation, query, update, delete, and guidance. This is within the ideal 3-15 range, and each tool earns its place without redundancy or bloat.

Completeness4/5

The toolset provides solid CRUD coverage for canvas elements (add, query, update, delete) plus a Mermaid import option and usage guidance. A minor gap is that there is no explicit tool to list existing canvases/rooms; agents must rely on prior room_id, which could be a friction point in new sessions, but core workflows are fully supported.

Resources

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