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Tomorrow Central: Cloud Cost Sentinel

Compare one price across regions (no account needed)

compare_regions
Read-only

Compare the same thing's price across AWS regions, cheapest first.

Use this when a user asks where something is cheapest, or what moving a workload
to another region would cost. `match` should be specific enough to identify one
priced thing, for example `t3.medium` or `gp3`.

`regions` limits the comparison; omit it to compare across every region the book
covers. Regions where the thing is not offered are listed separately rather than
silently dropped, because "not available there" is usually the more important
answer.

Region choice is rarely only about price. Data residency, latency to users, and
which services exist in a region all matter, and this tool speaks to none of them.
A cheaper region that cannot legally hold the data is not an option.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
matchYes
regionsNo
serviceYes
quantityNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.4/5.0
Behavior5/5

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

Annotations only flag read-only. Description adds output ordering ('cheapest first'), unavailable-region handling ('listed separately rather than silently dropped'), and a limitation caveat (data residency, latency, service availability). This goes well beyond the annotation.

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?

Purpose is front-loaded in the first sentence, then usage trigger, parameter guidance, and a caveat. Each paragraph adds distinct value without redundancy.

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?

Covers output ordering ('cheapest first'), absence behavior, and a key business limitation. However, missing explicit directions for the 'service' parameter and no mention of the return shape (e.g., unit, currency) prevent a 5.

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 descriptions are 0%, so the description must carry parameter meaning. It clearly explains 'match' and 'regions', but says nothing about required 'service' or optional 'quantity'. Partial coverage, so a middle score.

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?

Compare the same thing's price across AWS regions, cheapest first.

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?

It explicitly says 'Use this when a user asks what moving a workload to another region would cost,' giving a clear trigger condition. It does not name alternatives (e.g., price_lookup, compare_architectures), but the condition is specific enough to guide selection.

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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