Hopi

JSON to CSV converter

hopi_json_to_csv

Read-onlyIdempotent

Convert a JSON array of objects into CSV. The union of all keys becomes the header row in first-seen order, missing keys become empty cells, and nested objects or arrays are written back as compact JSON in the cell. Output follows RFC 4180 quoting. Source: https://hopi.co.uk/json-to-csv/

Input Schema

TableJSON Schema

Name	Required	Description	Default
`json`	Yes	A JSON array of objects to convert

Output Schema

TableJSON Schema

Name	Required	Description
`csv`	No
`rows`	No
`columns`	No
`headers`	No
`summary`	Yes
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026
- addedOutput schema / required
```
Added value: +[
+  "source_url",
+  "summary"
+]
```
First observedSep 20, 2026

TDQS

A4.7/5.0

Behavior5/5

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

Annotations already declare read-only, idempotent, and non-destructive. The description adds rich behavioral context: union of keys as header, first-seen order, empty cells for missing keys, compact JSON for nested values, RFC 4180 quoting, and a source URL. No contradiction.

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?

Two efficient sentences that front-load the core purpose, then pack in essential behavioral specifics without fluff. The source URL is relevant and non-intrusive.

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 single-parameter tool with an output schema, the description covers all critical behaviors: input format, conversion rules, quoting, and even source. Nothing an agent needs to call it correctly is missing.

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 schema describes the single 'json' parameter as 'A JSON array of objects to convert', and the tool description expands on conversion rules (header, missing keys, nested handling). With 100% schema coverage, the baseline is 3, but the description adds meaningful detail beyond the 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?

States the specific action 'Convert a JSON array of objects into CSV' with precise details on header generation, missing keys, nested objects, and quoting. Clearly distinguishes from sibling tools like hopi_csv_to_json.

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?

The description clearly conveys the tool's purpose, so an agent knows when to use it (JSON to CSV conversion). However, it does not explicitly mention when not to use it or name alternative tools, though the sibling list makes the inverse obvious.

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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