Hopi

Savings goal calculator

hopi_savings_goal_calculator

Read-onlyIdempotent

Plan a savings goal, compounded monthly. Mode 'time' works out how long a monthly deposit takes to reach a target. Mode 'monthly' works out the monthly saving needed to reach a target within a number of years. Both take an optional starting balance and an annual interest rate. Amounts in GBP. Source: https://hopi.co.uk/savings-goal-calculator/

Input Schema

TableJSON Schema

Name	Required	Description
`mode`	Yes	'time' finds the time to reach the goal; 'monthly' finds the monthly saving needed
`rate`	Yes	Annual interest rate as a percentage
`start`	No	Starting balance in GBP (default 0)
`years`	No	Monthly mode: number of years to reach the goal
`target`	Yes	Savings target in GBP (greater than zero)
`monthly`	No	Time mode: monthly deposit in GBP

Output Schema

TableJSON Schema

Name	Required	Description
`mode`	Yes
`rate`	Yes
`start`	Yes
`months`	Yes
`target`	Yes
`monthly`	No
`summary`	Yes
`interest`	Yes
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)
`timeToReach`	No
`totalPaidIn`	Yes
`finalBalance`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026

addedOutput schema / required

Added value: +[
+  "finalBalance",
+  "interest",
+  "mode",
+  "months",
+  "rate",
+  "source_url",
+  "start",
+  "summary",
+  "target",
+  "totalPaidIn"
+]

First observedSep 20, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already establish that the tool is read-only, idempotent, and non-destructive. The description adds valuable behavioral detail beyond that: compounding is monthly, amounts are in GBP, and the calculation supports an optional starting balance and annual interest rate.

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?

The description is compact and well-structured: a one-line purpose, two mode explanations, shared optional parameters, currency context, and a source link. Every sentence contributes useful information without redundancy.

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?

Given the rich schema, 100% parameter coverage, output schema existence, and annotations, the description provides the essential contextual facts—monthly compounding, mode behavior, optional inputs, and currency—that an agent needs to invoke this tool correctly.

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 coverage is 100%, and every parameter already has a meaningful description. The description adds a helpful prose summary of the mode-dependent roles of 'monthly' and 'years', but it does not significantly extend what the schema already provides.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly identifies the tool as a savings goal planner with monthly compounding and explains both modes: 'time' for duration and 'monthly' for required monthly deposit. It is specific and understandable, but it does not explicitly differentiate itself from related sibling tools such as the compound interest calculator.

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 gives clear mode-based usage context: use 'time' when you have a monthly deposit and want the time to reach a target, and use 'monthly' when you have a time frame and want the required monthly saving. It does not explicitly state when not to use this tool or mention alternatives among siblings.

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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