Yappman Data Supermarket Price Snapshots

Product classes with the largest index moves

get_class_movers

Read-onlyIdempotent

Returns the product classes (e.g. dairy-eggs) whose index moved most, week on week, in one published week: the largest rises and falls, each with its matched-product count and a thinBase flag where a class rests on few products. Classes only: no retailers, no products, no prices. Index changes, not price changes paid; not a CPI. Omit vintage for the latest week.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "market": "<market>"
    },
    "name": "get_class_movers"
  }
}

Input Schema

Name	Required	Description
`limit`	No	Classes per direction, 1 to 10. Omit for 5.
`market`	Yes	uk or au. Example: "au".
`vintage`	No	ISO week, e.g. "2026-W45". Omit for the latest published week.
`direction`	No	"up" for rises or "down" for falls. Omit for both.

Output Schema

Name	Required	Description	Default
`up`	No
`asOf`	Yes
`base`	No
`down`	No
`limit`	Yes
`notes`	Yes
`title`	No
`credit`	Yes
`market`	Yes
`notCpi`	Yes
`vintage`	Yes
`publishedAt`	No
`classesConsidered`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 12, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare read-only, idempotent, closed-world behavior, so the description adds genuine value beyond them: it discloses per-item fields (matched-product count, thinBase flag), explains what thinBase means (small product base), and clarifies that the metric is index change rather than price change. It stops short of covering boundary behavior, such as what a vintage with no published data yields.

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?

Front-loaded with what is returned, then the item fields, then the negative scope, then the semantic caveat. Every clause carries information and nothing redundant is present despite the density.

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?

An output schema exists so return values need no further explanation, annotations cover safety, and the description covers scope, ranking direction, and caveats for a 4-parameter read tool. A note on empty-vintage or single-direction results would close the remaining gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents market, vintage, direction and limit. The description's only parameter-relevant content ('Omit vintage for the latest week') restates the schema's own note, adding no new syntax or constraint. Baseline 3 applies.

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 (returns product classes with the largest week-on-week index moves), gives a concrete example ('dairy-eggs'), and delimits scope with 'Classes only: no retailers, no products, no prices' plus 'not a CPI'. An agent can distinguish this from a price-index tool without opening any schema.

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?

Usage context is clear through exclusions: it is for index movement, not prices paid, and it is not a CPI, which routes the agent away from price-oriented siblings. It also tells the agent to omit vintage for the latest week. It does not explicitly name an alternative tool, so it falls short of a full when/when-not/alternative statement.

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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