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Utility Matrix

by io.github.helphub369
OverviewDiscussionsAdmin

EC2 Cost Calculator

ec2-cost-calculator
Read-onlyIdempotent

Use when a user asks about EC2 cost. Given instance type and hours, returns monthly cost and DO-equivalent savings estimate.

Input Schema

NameRequiredDescriptionDefault
osNoos used by this deterministic tool.
instance_typeYesinstance type used by this deterministic tool.
hours_per_monthNohours per month used by this deterministic tool.

Output Schema

NameRequiredDescriptionDefault
next_stepYes
do_savingsYes
annual_costYes
hourly_rateYes
output_tierYes
monthly_costYes
signal_valueYes
next_step_urlYes
why_follow_upYes
interpretationYes
affiliate_contextNo
computation_basisYes
do_equivalent_monthlyYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • changedInput schema / properties / hours_per_month / examples
      Previous value: -[
-  1
-]New value: +[
+  730
+]
    • changedInput schema / properties / instance_type / examples
      Previous value: -[
-  "example"
-]New value: +[
+  "t3.medium"
+]
    • changedInput schema / properties / os / examples
      Previous value: -[
-  "example"
-]New value: +[
+  "Linux"
+]
  2. Changed6 schema fields changed
    • addedInput schema / properties / hours_per_month / description
      Added value: +"hours per month used by this deterministic tool."
    • addedInput schema / properties / hours_per_month / examples
      Added value: +[
+  1
+]
    • addedInput schema / properties / instance_type / description
      Added value: +"instance type used by this deterministic tool."
    • addedInput schema / properties / instance_type / examples
      Added value: +[
+  "example"
+]
    • addedInput schema / properties / os / description
      Added value: +"os used by this deterministic tool."
    • addedInput schema / properties / os / examples
      Added value: +[
+  "example"
+]
  3. Changed1 schema field changed
    • 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"
+    },
+    "annual_cost": {
+      "type": "number"
+    },
+    "computation_basis": {
+      "type": "string"
+    },
+    "do_equivalent_monthly": {
+      "type": "number"
+    },
+    "do_savings": {
+      "type": "number"
+    },
+    "hourly_rate": {
+      "type": "number"
+    },
+    "interpretation": {
+      "type": "string"
+    },
+    "monthly_cost": {
+      "type": "number"
+    },
+    "next_step": {
+      "type": "string"
+    },
+    "next_step_url": {
+      "type": "string"
+    },
+    "output_tier": {
+      "type": "string"
+    },
+    "signal_value": {
+      "type": "number"
+    },
+    "why_follow_up": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "annual_cost",
+    "computation_basis",
+    "do_equivalent_monthly",
+    "do_savings",
+    "hourly_rate",
+    "interpretation",
+    "monthly_cost",
+    "next_step",
+    "next_step_url",
+    "output_tier",
+    "signal_value",
+    "why_follow_up"
+  ],
+  "type": "object"
+}
  4. Changed1 schema field changed
    • addedInput schema / additionalProperties
      Added value: +false
  5. First observed

TDQS

B3.4/5.0
Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds useful context that it returns a DO-equivalent savings estimate, a behavior not evident from the name. It doesn't add constraints, defaults, or rate-limit context.

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?

Two tight sentences with the trigger front-loaded ahead of the return description; every clause earns its place. Minor imprecision: it implies hours is needed, yet only instance_type is required.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values needn't be re-explained, and annotations carry safety. Remaining gaps are the optional status/default of hours_per_month and os, plus no sibling routing among numerous cost calculators.

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%, so all three parameters are already documented in the schema, establishing the baseline of 3. The description mentions only instance type and hours, omitting os, and adds no format or default details beyond the schema.

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?

States a specific verb+resource: returns monthly cost and a DO-equivalent savings estimate for EC2. It is clearly about EC2, which separates it from the many sibling cost calculators (egress, pipeline, query). However, it does not explicitly name or contrast against those siblings.

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

Usage Guidelines3/5

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

"Use when a user asks about EC2 cost" gives a clear trigger condition. But there is no when-not guidance and no routing to alternatives such as rightsizing-calculator or reserved-instance-breakeven, leaving the agent to infer boundaries among many overlapping cost tools.

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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