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Kookerella-Ltd

Excel MCP Server (FsOpenXmlDsl)

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create_workbook_from_json

Build an Excel workbook from JSON data, including styles, tables, and charts, and save it to a specified file path.

Instructions

Builds a new Excel workbook from JSON matching the shape generate_json produces (see the main library repo's Json.schema.json) and saves it to disk - the inverse of generate_json. The JSON-side equivalent of create_workbook_from_xml, for a caller that already produces data as JSON and wants to reach Excel without learning the OOXML schema or this library's own F#/C# API. Covers the same worksheet/workbook-level feature set generate_json does; unlike create_workbook, this isn't limited to plain cell values - styling, tables, charts, and every other modeled feature can be expressed in the JSON.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
jsonYesThe workbook JSON content - an object matching Json.schema.json's root shape.
pathYesOutput file path, e.g. "C:\reports\invoice.xlsx". The directory must already exist.
Behavior3/5

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

There are no annotations, so the description carries the burden. It clearly discloses the side-effect of saving to disk and the inverse relationship to generate_json. However, it does not mention overwrite behavior, failure modes, validation of the JSON, or filesystem permissions, which are relevant for a mutation tool.

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 thorough and front-loaded with the core action, but longer than strictly necessary. Every sentence earns its place by clarifying the inverse relationship, sibling tool, and feature scope, though a more compact phrasing could preserve the same value with less verbosity.

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?

Despite having no output schema and no annotations, the description gives an agent enough context to invoke correctly: it identifies the expected JSON shape, the output destination, and how this tool relates to alternative sibling tools. It is somewhat incomplete on overwrite behavior and errors, but those are minor gaps for a tool with only two well-described parameters.

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 input schema already covers both parameters fully, so baseline is 3. The description adds value by explaining that json must match the shape generate_json produces, linking to Json.schema.json, and enumerating the feature set expressible in JSON, which clarifies what content the json parameter can hold beyond the schema's generic wording.

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?

This says it builds a new Excel workbook from JSON and saves it to disk – a specific verb, resource, and output. It also differentiates itself from siblings: inverse of generate_json, JSON-side equivalent of create_workbook_from_xml, and distinct from create_workbook because it supports styling, tables, charts, and every other modeled feature.

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?

It explicitly states when to use it: when a caller already has data as JSON and wants Excel without learning OOXML schema or the library's own F#/ C# API. It also names alternatives and exclusions: use create_workbook when only plain cell values are needed, and notes it covers the same feature set as generate_json.

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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