Ring Size Converter Skill

Overview

Ring Size Converter works through inside diameter in millimetres. A lookup table maps US sizes 3 to 14 in half sizes and UK letters F to Z plus Z+1 and Z+2 to diameters from 14.1 mm to 23.0 mm. The `size` and `from` parameters are converted to a diameter first; the `measurement` parameter, a diameter from 10 to 30 mm, skips that step and takes priority when both are sent.

For `from=us`, a size missing from the table is interpolated at 0.4 mm per step, so a quarter size still converts. For `uk` and `au`, the letter must be in the table or the call returns a 400. `eu` input is the inner circumference in millimetres (ISO 8653). `jp` and `ch` input are treated as a ring number equal to the inner circumference minus 40.

From the diameter, `circumference_mm` is diameter times pi, rounded to one decimal. `us` and `uk` are the table entries whose diameter is nearest, so output US sizes always land on a half size. `au` is the same letter as `uk`. `eu` is the circumference rounded to a whole millimetre. `jp` is the circumference minus 40, rounded (minimum 1). `ch` is the circumference minus 40, truncated to a whole number. `input_diameter_mm` and `conversions.diameter_mm` echo the diameter actually used, which for interpolated or `ch` input can carry more decimals than the table values.

On the Free plan `eu`, `jp`, `ch` and `au` are removed from `conversions`; the diameter, circumference, `us` and `uk` remain.

Live Test Ring Size Converter Skill Skill →

The tool

Once your client is connected to the VerveKit server, this appears in its tool list as RingSizeConverterSkill. It is read-only and open-world — it fetches and never mutates anything on your side — so most clients call it without asking you to confirm.

{
  "name": "RingSizeConverterSkill",
  "arguments": {
    "size": "7",
    "from": "us"
  }
}

You do not name the tool yourself; the model picks it. Asking about 7 in the terms this skill covers is enough for it to reach for RingSizeConverterSkill on its own — naming it explicitly also works, and is the way to force the call.

Connecting

One server URL covers every skill in the catalog, including this one. Authorization is OAuth: the client opens a browser once, and there is no key to paste into a config file.

{
  "mcpServers": {
    "vervekit": {
      "url": "https://api.vervekit.com/v1/mcp"
    }
  }
}

https://api.vervekit.com/v1/mcp

Per-client setup — Claude, Cursor, VS Code, ChatGPT — is on the MCP setup page.

Arguments

These are the properties on the tool's inputSchema, so a well-behaved client validates them before the call is made. Premium arguments are accepted on every plan but only take effect on plans that include them.

What the model gets back

The result carries a structuredContent object matching the tool's declared outputSchema, so a client reads fields without parsing prose. status is "ok" and error is null on success; a null field means the value was not available for that input, not that the call failed.

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{
  "status": "ok",
  "error": null,
  "data": {
    "input_diameter_mm": 17.3,
    "circumference_mm": 54.3,
    "conversions": {
      "diameter_mm": 17.3,
      "circumference_mm": 54.3,
      "us": 7,
      "uk": "N",
      "eu": 52,
      "jp": 17,
      "ch": -22,
      "au": "N"
    },
    "note": "Sizes are approximate. For accurate sizing, visit a jeweler."
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Failure modes

Errors come back as tool errors carrying a sentence the model can act on, not a bare status code. Error handling covers the full list.

A call costs 1 credit each time the tool actually runs; a model that reasons about the tool without calling it costs nothing.

Use cases

Jewelry E-commerce

Help customers find their ring size when purchasing from international jewelers and retailers

Gift Shopping

Convert ring sizes when buying jewelry gifts for people in different countries

Jewelry Sizing

Provide sizing tools for jewelers working with international customers and standards

Size Guides

Create comprehensive ring size conversion charts for jewelry product listings

Other ways to use Ring Size Converter Skill

Set up Ring Size Converter Skill on VerveKit, or reach the same source a different way. Your VerveKit account and credits work on all of them — one key, one balance.

Related

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