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t0knight
by t0knight

create_custom_widget

Create a custom widget that auto-fills the canvas width and height. Seed it with HTML, CSS, JS, and default model data; any omitted field uses the starter template.

Instructions

Create a single Custom Widget — the primary entrypoint of this MCP.

The widget is auto-sized to fill the main canvas: full width (all columns) and a
height measured from the canvas's available pixel height. Size and position are not
configurable. `html`/`css`/`js` seed its source; any omitted field falls back to
Appsmith's starter template. `default_model` seeds the data the widget reads via
`appsmith.model` (dict or JSON string). Seeded source is written to both `srcDoc` and
`uncompiledSrcDoc` so a reload can't revert it (`synced: true`).
Returns `{widgetId, widgetName, type, parent, columns, rows, measuredHeightPx, synced}`.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
jsNo
cssNo
htmlNo
nameNo
default_modelNo
Behavior4/5

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

The description discloses important behaviors: auto-sizing to full width/height, non-configurable size/position, fallback to starter template for omitted fields, seeding of default_model, and syncing of source to both srcDoc and uncompiledSrcDoc. Since no annotations are provided, the description carries full burden and does so well.

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?

The description is a single, focused paragraph with clear structure: purpose first, then details. It is concise with no fluff, though could be slightly more structured with bullet points.

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

Completeness3/5

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

The description covers the return format and syncing behavior, but lacks prerequisites (e.g., whether a page must exist) and does not mention any related tools. Given the complexity and no output schema, it is adequate but not fully 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?

The description explains the purpose of html/css/js (seed source), default_model (seed data), and mentions that omitted fields fall back to starter template. It adds meaning beyond the input schema, though the name parameter is not explicitly described. Schema coverage is 0%, so description compensates effectively.

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 clearly states 'Create a single Custom Widget — the primary entrypoint of this MCP', using a specific verb and resource. It distinguishes itself from sibling tools like add_widgets and update_custom_widget by positioning itself as the primary creation tool.

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

Usage Guidelines3/5

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

The description implies this is the main creation tool but does not explicitly state when to use it versus alternatives, nor does it provide when-not-to-use conditions. No alternatives are named.

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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