NBG Rates

Convert via NBG rate

nbg_convert

Read-onlyIdempotent

Convert an amount between currencies at the official NBG rate for a calendar date, including GEL pairs and weekend/holiday carry-over rates.

Instructions

Converts an amount between two currencies using the official NBG rate in force on a calendar date. Either side may be GEL; a pair without GEL is converted through GEL (via: "GEL"). Show resultRounded as the amount; result is the unrounded value for further calculation. Dates are calendar days in Tbilisi; the default is today. NBG sets a rate on business days around 17:00 Tbilisi time, valid from the next calendar day until the next rate, so after 17:00 tomorrow can be requested by date. Sundays, Mondays and days after a public holiday have no rate of their own: the rate in force was set earlier and is returned with carriedOver true and effectiveDate set to the day it took effect. Quote effectiveDate when carriedOver is true. A date whose rate NBG has not published yet returns an error, never a guess.

Input Schema

TableJSON Schema

Name	Required	Description
`to`	Yes	ISO 4217 code, or GEL.
`date`	No	Calendar date YYYY-MM-DD whose official rate to apply. Defaults to today in Tbilisi.
`from`	Yes	ISO 4217 code, or GEL.
`amount`	Yes	Amount in the "from" currency. May be negative.

Output Schema

TableJSON Schema

Name	Required	Description
`to`	Yes
`via`	Yes
`from`	Yes
`rate`	Yes	One unit of "from" expressed in "to"
`amount`	Yes
`result`	Yes	Unrounded
`carriedOver`	Yes	true when the rate in force on requestedDate took effect on an earlier day; it is still the official rate
`effectiveDate`	Yes	Calendar date the returned rate took effect, as published by NBG
`requestedDate`	Yes
`resultRounded`	Yes	result rounded half up to 2 decimals from the exact value; the amount to show. JSON drops trailing zeros, so 3.90 arrives as 3.9. Exact up to about 7e13 in the target currency; above that the nearest double.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 16, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description adds substantial behavior beyond them: rate publication at ~17:00 Tbilisi with next-day validity, carried-over rates on Sundays/Mondays/post-holidays flagged via carriedOver and effectiveDate, and an explicit 'error, never a guess' failure mode. That is exactly the extra context an agent needs to interpret results.

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?

One dense paragraph, front-loaded with the core purpose, then usage, then output/date semantics. Every sentence carries information, though the 17:00/carried-over timing block is lengthy and could be tightened without losing meaning.

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?

For a 4-parameter conversion tool with annotations and an output schema, the description covers input constraints, the GEL routing rule, output-field usage (resultRounded vs result), date/rollover behavior, and error semantics. Nothing an agent needs to call it correctly is missing.

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: it constrains 'from'/'to' to currency sides (one may be GEL), explains the implicit GEL conversion and the 'via' output value, and clarifies 'date' is a Tbilisi calendar day defaulting to today with post-17:00 forward availability.

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 opening sentence names a specific verb and resource ('Converts an amount between two currencies') and pins the rate source and effective-date semantics. This clearly separates it from nbg_convert_many (bulk) and nbg_rate_history (historical listing), so an agent can route correctly without opening the 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?

It gives concrete usage context: either side may be GEL, non-GEL pairs route through GEL with a 'via' value, and the date defaults to today in Tbilisi. It also implies the single-pair use case but never explicitly names an alternative tool (e.g. nbg_convert_many) or states exclusions, so it stops short of a full when/when-not 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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