CurrencyGuard Guard Pricing

Historic Best/Worst FX Performance

get_historic_best_worst

Read-only

Analyze historic best/worst FX performance for a currency pair over a Guard's duration. Uses Bank of England historic rates. Returns a 'performances' array with 6 entries — BEST and WORST for each of three lookback periods (5, 10, 25 years). Each entry contains: performanceType (BEST or WORST), periodInYears (5, 10 or 25), windowSizeInDays, startDate/endDate, startRate/endRate, performancePercentage, startAmount, finalAmount, deltaAmount (in the window's own money), finalAmountToday, deltaAmountToday (the same move applied to today's amount). For Guard-Pay: negative delta = cost decreased = BEST; positive delta = cost increased = WORST. For Guard-Receive: positive delta = receipt increased = BEST; negative delta = receipt decreased = WORST. When there is a preceding price_guard call, the parameters must match it, including payReceive (PAY or RECEIVE). WHEN TO CALL. Only when the user asks for historic performance, best or worst cases, or historic context. Never to answer "what can I do" or "what would you do". If there is no price_guard quote, leave guardAmount empty; do not call price_guard only to fill it. IF IT FAILS. A result with valid: false has no data. Say that historic figures are unavailable and stop. Do not show the table and do not estimate any figure.

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": {
      "guardCurrency": "<guardCurrency>",
      "foreignCurrency": "<foreignCurrency>",
      "payReceive": "<payReceive>",
      "foreignAmount": "<foreignAmount>",
      "settlementDate": "<settlementDate>"
    },
    "name": "get_historic_best_worst"
  }
}

Input Schema

Name	Required	Description
`payReceive`	Yes	MUST be the exact same payReceive value you used in price_guard (PAY or RECEIVE). Do NOT change it.
`guardAmount`	No	Guard amount in base/home currency from the Guard quote (the guardAmount field from the price_guard response). Leave it empty when there is no quote, and the tool uses today's indicative mid spot rate instead, so a risk question needs no price first.
`foreignAmount`	Yes	Amount in foreign currency — MUST match foreignAmount from price_guard
`guardCurrency`	Yes	Home/base currency ISO code — MUST match guardCurrency from price_guard
`settlementDate`	Yes	Settlement date in ISO format YYYY-MM-DD — MUST match settlementDate from price_guard
`foreignCurrency`	Yes	Foreign currency ISO code — MUST match foreignCurrency from price_guard

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedNov 5, 2026

changedInput schema / properties / guardAmount / description

Previous value: -"Guard amount in base/home currency from the Guard quote (the guardAmount field from the price_guard response). Optional: leave it empty when there is no quote, and the tool uses today's indicative mid spot rate instead, so a risk question needs no price first."New value: +"Guard amount in base/home currency from the Guard quote (the guardAmount field from the price_guard response). Leave it empty when there is no quote, and the tool uses today's indicative mid spot rate instead, so a risk question needs no price first."

Changed2 schema fields changedOct 17, 2026

changedInput schema / properties / guardAmount / description

Previous value: -"Guard amount in base/home currency from the Guard quote (the guardAmount field from the price_guard response)"New value: +"Guard amount in base/home currency from the Guard quote (the guardAmount field from the price_guard response). Optional: leave it empty when there is no quote, and the tool uses today's indicative mid spot rate instead, so a risk question needs no price first."

changedInput schema / required

Previous value: -[
-  "guardCurrency",
-  "foreignCurrency",
-  "payReceive",
-  "foreignAmount",
-  "guardAmount",
-  "settlementDate"
-]New value: +[
+  "guardCurrency",
+  "foreignCurrency",
+  "payReceive",
+  "foreignAmount",
+  "settlementDate"
+]

Changed8 schema fields changedOct 16, 2026
- addedInput schema / $schema
```
Added value: +"http://json-schema.org/draft-07/schema#"
```
- addedInput schema / properties / foreignAmount / exclusiveMinimum
```
Added value: +0
```
- addedInput schema / properties / foreignCurrency / maxLength
```
Added value: +3
```
- addedInput schema / properties / foreignCurrency / minLength
```
Added value: +3
```
- addedInput schema / properties / guardAmount / exclusiveMinimum
```
Added value: +0
```
- addedInput schema / properties / guardCurrency / maxLength
```
Added value: +3
```
- addedInput schema / properties / guardCurrency / minLength
```
Added value: +3
```
- addedInput schema / properties / payReceive / enum
```
Added value: +[
+  "PAY",
+  "RECEIVE"
+]
```
Changed1 schema field changedMay 11, 2026
- removedInput schema / additionalProperties
```
Removed value: -false
```
First observedApr 22, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered; the description layers on genuinely new behavior: BoE as the rate source, the PAY/RECEIVE sign interpretation for BEST vs WORST, the requirement to mirror a preceding price_guard call, and the IF IT FAILS contract (valid:false means no data, do not estimate). The only gap is that it doesn't say anything about ordering, latency, or parameter-mismatch handling beyond the mandate to match.

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?

The prose is dense but organized into front-loaded purpose, a return-shape block, a WHEN TO CALL block, and a failure block, so an agent can skim to the relevant part. The long enumeration of result fields is justified because there is no output schema, though a few clauses (e.g. the repeated delta explanations) could be tightened.

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?

With no output schema, the description carries the return-value burden and does so thoroughly, field by field, while also covering the no-quote, no-price_guard, and failure paths. An agent has everything needed to call it and to report results correctly after a valid:false response.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: it explains why guardAmount may be omitted (today's indicative mid is used instead) and what payReceive implies for interpreting delta as cost or receipt movement. That is interpretive context the schema does not carry.

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?

The description opens with a specific verb and resource ('Analyze historic best/worst FX performance for a currency pair over a Guard's duration'), names the data source (Bank of England rates), and enumerates what comes back (6 entries covering 5/10/25-year BEST and WORST windows). An agent can distinguish this from price_guard or compare_guard_with_forward from the text alone.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is an explicit WHEN TO CALL block with both the positive trigger ('user asks for historic performance, best or worst cases, or historic context') and the negative one ('Never to answer what can I do / what would you do'), plus the guardAmount fallback rule forbidding an unnecessary price_guard call. Nothing is left to inference.

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

All CurrencyGuard Guard Pricing tools Inspect

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