within

Convert a size

convert_size

Read-onlyIdempotent

Convert ring, shoe, clothing, suit, belt, hat, or designer sizes across countries using sourced size tables and return the page showing the answer.

Instructions

Turn a size in one system into every other system: rings, shoes, clothing, suits, belts and hats, or one designer's own chart (pass designer as its slug, e.g. 'nike'). Answers only from the size tables on shopwithin.co/sizes, where every row comes from a named source with the day it was read, and returns the page that shows the answer. Use this when someone asks what their size is in another country's system (EU to US shoe size, a ring size chart), which size to take in a designer, or how a designer's sizes run. Call it without from and size to list the systems and tables a kind or a designer has.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "convert_size"
  }
}

Input Schema

Name	Required	Description
`to`	No	Optional: one system key to lead the answer with.
`from`	No	The system the size is written in, as a key this tool lists, e.g. 'us', 'uk', 'eu'.
`kind`	No	What is being sized: rings, shoes, clothing, suits, belts or hats.
`size`	No	The size as printed, e.g. '7', 'N 1/2', '42', 'M'.
`table`	No	Optional: one table or chart id this tool lists.
`designer`	No	A designer's slug, as in shopwithin.co/designers/<slug>, to read that designer's own charts instead of a kind.
`department`	No	Optional: only women's or men's tables.

Output Schema

Name	Required	Description	Default
`note`	Yes
`kinds`	Yes
`scope`	Yes
`status`	Yes
`tables`	Yes
`matches`	Yes
`sources`	Yes
`systems`	Yes
`page_url`	Yes
`designers`	Yes
`size_page_url`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.1Nov 11, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds real value beyond that: answers are constrained to the size tables on shopwithin.co/sizes, every row carries a named source and read date, and it returns the page showing the answer. It does not describe behavior for unknown sizes or missing tables.

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?

Front-loaded with the core verb and resource, then scope, provenance and the discovery-mode tip. Dense but every clause carries information; the second sentence is long and could be split for readability.

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?

With an output schema, full parameter coverage and safety annotations, the description is nearly complete for a zero-required-parameter read tool. The only omission is edge-case behavior (unmatched size, kind/designer conflict), which is minor in context.

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?

Schema description coverage is 100%, so the baseline is 3. The description adds meaning on top: designer is passed as a slug (e.g. 'nike'), omitting from and size switches to a listing of systems/tables, and 'to' leads the answer with one system. That clarifies the semantics of optional-parameter omission, which the schema alone does not.

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 a specific verb and resource ('Turn a size in one system into every other system') and enumerates the sizing domains (rings, shoes, clothing, suits, belts, hats) plus the designer-chart variant. This is clearly distinct from siblings like piece_fit or search_pieces, which concern garments rather than conversion tables.

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?

Gives explicit trigger conditions: cross-country size questions, ring size charts, which size to take in a designer, and how a designer's sizes run. It also documents a discovery mode ('Call it without from and size to list the systems and tables'). It does not name any sibling as an alternative or state when-not to use it, so it stops short of a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.