Utility Matrix

Reserved Instance Breakeven Calculator

reserved-instance-breakeven

Read-onlyIdempotent

Use this when a user asks whether to buy Reserved Instances or stay on On-Demand, or how long an RI takes to pay for itself. Takes On-Demand and RI monthly costs plus optional upfront fees (0 when omitted). Judges the 1-year and 3-year terms separately and returns each break-even month and net saving. It recommends a term only when that term saves money over its own length, and prefers 3 years only when it beats three 1-year terms over 36 months at current prices.

Input Schema

Name	Required	Description
`od_monthly`	Yes	On-Demand cost per month in USD.
`ri_1yr_monthly`	Yes	1-year Reserved Instance cost per month in USD, excluding the upfront fee.
`ri_1yr_upfront`	No	1-year upfront fee in USD; 0 when omitted (no-upfront RI).
`ri_3yr_monthly`	Yes	3-year Reserved Instance cost per month in USD, excluding the upfront fee.
`ri_3yr_upfront`	No	3-year upfront fee in USD; 0 when omitted (no-upfront RI).

Output Schema

Name	Required	Description	Default
`severity`	Yes
`next_step`	Yes
`next_step_url`	Yes
`why_follow_up`	Yes
`interpretation`	Yes
`breakeven_months`	No
`recommended_term`	Yes
`affiliate_context`	No
`computation_basis`	Yes
`net_savings_1yr_usd`	Yes
`net_savings_3yr_usd`	Yes
`breakeven_months_3yr`	No
`monthly_saving_1yr_usd`	Yes
`monthly_saving_3yr_usd`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed19 schema fields changedOct 11, 2026

changedInput schema / properties / od_monthly / description

Previous value: -"od monthly used by this deterministic tool."New value: +"On-Demand cost per month in USD."

changedInput schema / properties / od_monthly / examples
```
Previous value: -[
-  1
-]New value: +[
+  450
+]
```
addedInput schema / properties / od_monthly / exclusiveMinimum
```
Added value: +0
```

changedInput schema / properties / ri_1yr_monthly / description

Previous value: -"ri 1yr monthly used by this deterministic tool."New value: +"1-year Reserved Instance cost per month in USD, excluding the upfront fee."

changedInput schema / properties / ri_1yr_monthly / examples
```
Previous value: -[
-  1
-]New value: +[
+  280
+]
```
addedInput schema / properties / ri_1yr_monthly / minimum
```
Added value: +0
```

changedInput schema / properties / ri_1yr_upfront / description

Previous value: -"ri 1yr upfront used by this deterministic tool."New value: +"1-year upfront fee in USD; 0 when omitted (no-upfront RI)."

changedInput schema / properties / ri_1yr_upfront / examples
```
Previous value: -[
-  1
-]New value: +[
+  0
+]
```
addedInput schema / properties / ri_1yr_upfront / minimum
```
Added value: +0
```

changedInput schema / properties / ri_3yr_monthly / description

Previous value: -"ri 3yr monthly used by this deterministic tool."New value: +"3-year Reserved Instance cost per month in USD, excluding the upfront fee."

changedInput schema / properties / ri_3yr_monthly / examples
```
Previous value: -[
-  1
-]New value: +[
+  180
+]
```
addedInput schema / properties / ri_3yr_monthly / minimum
```
Added value: +0
```

changedInput schema / properties / ri_3yr_upfront / description

Previous value: -"ri 3yr upfront used by this deterministic tool."New value: +"3-year upfront fee in USD; 0 when omitted (no-upfront RI)."

changedInput schema / properties / ri_3yr_upfront / examples
```
Previous value: -[
-  1
-]New value: +[
+  0
+]
```
addedInput schema / properties / ri_3yr_upfront / minimum
```
Added value: +0
```
addedOutput schema / properties / breakeven_months_3yr
```
Added value: +{
+  "type": "number"
+}
```
addedOutput schema / properties / monthly_saving_1yr_usd
```
Added value: +{
+  "type": "number"
+}
```
addedOutput schema / properties / monthly_saving_3yr_usd
```
Added value: +{
+  "type": "number"
+}
```

changedOutput schema / required

Previous value: -[
-  "computation_basis",
-  "interpretation",
-  "net_savings_1yr_usd",
-  "net_savings_3yr_usd",
-  "next_step",
-  "next_step_url",
-  "recommended_term",
-  "severity",
-  "why_follow_up"
-]New value: +[
+  "computation_basis",
+  "interpretation",
+  "monthly_saving_1yr_usd",
+  "monthly_saving_3yr_usd",
+  "net_savings_1yr_usd",
+  "net_savings_3yr_usd",
+  "next_step",
+  "next_step_url",
+  "recommended_term",
+  "severity",
+  "why_follow_up"
+]

Changed1 schema field changedOct 1, 2026

changedOutput schema / required

Previous value: -[
-  "breakeven_months",
-  "computation_basis",
-  "interpretation",
-  "net_savings_1yr_usd",
-  "net_savings_3yr_usd",
-  "next_step",
-  "next_step_url",
-  "recommended_term",
-  "severity",
-  "why_follow_up"
-]New value: +[
+  "computation_basis",
+  "interpretation",
+  "net_savings_1yr_usd",
+  "net_savings_3yr_usd",
+  "next_step",
+  "next_step_url",
+  "recommended_term",
+  "severity",
+  "why_follow_up"
+]

Changed12 schema fields changedSep 28, 2026

addedInput schema / properties / od_monthly / description

Added value: +"od monthly used by this deterministic tool."

addedInput schema / properties / od_monthly / examples
```
Added value: +[
+  1
+]
```

addedInput schema / properties / ri_1yr_monthly / description

Added value: +"ri 1yr monthly used by this deterministic tool."

addedInput schema / properties / ri_1yr_monthly / examples
```
Added value: +[
+  1
+]
```

addedInput schema / properties / ri_1yr_upfront / description

Added value: +"ri 1yr upfront used by this deterministic tool."

addedInput schema / properties / ri_1yr_upfront / examples
```
Added value: +[
+  1
+]
```

addedInput schema / properties / ri_3yr_monthly / description

Added value: +"ri 3yr monthly used by this deterministic tool."

addedInput schema / properties / ri_3yr_monthly / examples
```
Added value: +[
+  1
+]
```

addedInput schema / properties / ri_3yr_upfront / description

Added value: +"ri 3yr upfront used by this deterministic tool."

addedInput schema / properties / ri_3yr_upfront / examples
```
Added value: +[
+  1
+]
```
addedOutput schema / properties / computation_basis
```
Added value: +{
+  "type": "string"
+}
```

changedOutput schema / required

Previous value: -[
-  "breakeven_months",
-  "interpretation",
-  "net_savings_1yr_usd",
-  "net_savings_3yr_usd",
-  "next_step",
-  "next_step_url",
-  "recommended_term",
-  "severity",
-  "why_follow_up"
-]New value: +[
+  "breakeven_months",
+  "computation_basis",
+  "interpretation",
+  "net_savings_1yr_usd",
+  "net_savings_3yr_usd",
+  "next_step",
+  "next_step_url",
+  "recommended_term",
+  "severity",
+  "why_follow_up"
+]

Changed1 schema field changedJul 15, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": false,
+  "properties": {
+    "affiliate_context": {
+      "additionalProperties": false,
+      "properties": {
+        "affiliate": {
+          "type": "string"
+        },
+        "cta_label": {
+          "type": "string"
+        },
+        "disclosure": {
+          "type": "string"
+        },
+        "framing": {
+          "type": "string"
+        },
+        "posture": {
+          "enum": [
+            "secondary"
+          ],
+          "type": "string"
+        },
+        "slot_id": {
+          "type": "string"
+        },
+        "url": {
+          "type": "string"
+        },
+        "variant": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "affiliate",
+        "cta_label",
+        "disclosure",
+        "framing",
+        "posture",
+        "slot_id",
+        "url",
+        "variant"
+      ],
+      "type": "object"
+    },
+    "breakeven_months": {
+      "type": "number"
+    },
+    "interpretation": {
+      "type": "string"
+    },
+    "net_savings_1yr_usd": {
+      "type": "number"
+    },
+    "net_savings_3yr_usd": {
+      "type": "number"
+    },
+    "next_step": {
+      "type": "string"
+    },
+    "next_step_url": {
+      "type": "string"
+    },
+    "recommended_term": {
+      "type": "string"
+    },
+    "severity": {
+      "type": "string"
+    },
+    "why_follow_up": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "breakeven_months",
+    "interpretation",
+    "net_savings_1yr_usd",
+    "net_savings_3yr_usd",
+    "next_step",
+    "next_step_url",
+    "recommended_term",
+    "severity",
+    "why_follow_up"
+  ],
+  "type": "object"
+}

Changed1 schema field changedJul 13, 2026
- addedInput schema / additionalProperties
```
Added value: +false
```
First observedJun 29, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description goes well beyond them by disclosing the decision logic: terms are judged independently, a recommendation is made only when a term saves money over its own length, and 3-year is preferred only when it beats three consecutive 1-year terms. That is exactly the kind of hidden reasoning an agent needs to interpret or trust the result.

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?

Four dense sentences, no filler: trigger first, inputs second, output third, recommendation policy last. Every sentence carries distinct information and the ordering matches how an agent would use it.

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 an output schema present and annotations covering safety, the description supplies the remaining missing layer — the recommendation rules and separate per-term evaluation — so an agent knows not just how to call it but how to interpret and relay the result.

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% and the description mostly restates schema facts ('optional upfront fees (0 when omitted)'). It adds no syntax or semantics beyond what the parameter descriptions already say, so the 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?

Names a specific verb+resource (break-even calculation between Reserved Instances and On-Demand) and states the exact scope: judging 1-year and 3-year terms separately and returning each break-even month and net saving. No sibling in the list (ec2-cost-calculator, cloud-waste-calculator, total-cost-of-ownership-calculator) overlaps this specific decision, so an agent can route here without opening schemas.

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?

Front-loads an explicit trigger: 'Use this when a user asks whether to buy Reserved Instances or stay on On-Demand, or how long an RI takes to pay for itself.' That is clear when-to-use context, though it names no exclusions or alternative tools (e.g., when to prefer the general cost calculators instead).

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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