Utility Matrix

PostgreSQL Query Cost Estimator

query-cost-estimator

Read-onlyIdempotent

Estimate PostgreSQL sequential-scan and index-scan cost from table rows, table pages, selectivity, and storage type. Uses the same four-input model as the browser calculator.

Input Schema

Name	Required	Description
`table_rows`	Yes	table rows used by this deterministic tool.
`table_pages`	Yes	table pages used by this deterministic tool.
`storage_type`	Yes	storage type; accepted values: ssd, nvme, hdd, network.
`selectivity_pct`	Yes	selectivity expressed as a percentage.

Output Schema

Name	Required	Description	Default
`next_step`	Yes
`cost_ratio`	Yes
`index_pages`	Yes
`index_tuples`	Yes
`storage_type`	Yes
`next_step_url`	Yes
`why_follow_up`	Yes
`interpretation`	Yes
`index_scan_cost`	Yes
`random_page_cost`	Yes
`recommended_plan`	Yes
`affiliate_context`	No
`computation_basis`	Yes
`sequential_scan_cost`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 11, 2026

addedOutput schema / properties / storage_type
```
Added value: +{
+  "type": "string"
+}
```

changedOutput schema / required

Previous value: -[
-  "computation_basis",
-  "cost_ratio",
-  "index_pages",
-  "index_scan_cost",
-  "index_tuples",
-  "interpretation",
-  "next_step",
-  "next_step_url",
-  "random_page_cost",
-  "recommended_plan",
-  "sequential_scan_cost",
-  "why_follow_up"
-]New value: +[
+  "computation_basis",
+  "cost_ratio",
+  "index_pages",
+  "index_scan_cost",
+  "index_tuples",
+  "interpretation",
+  "next_step",
+  "next_step_url",
+  "random_page_cost",
+  "recommended_plan",
+  "sequential_scan_cost",
+  "storage_type",
+  "why_follow_up"
+]

Changed18 schema fields changedSep 28, 2026

removedInput schema / properties / query

Removed value: -{
-  "description": "SQL query to analyze",
-  "type": "string"
-}

addedInput schema / properties / selectivity_pct

Added value: +{
+  "description": "selectivity expressed as a percentage.",
+  "examples": [
+    1
+  ],
+  "maximum": 100,
+  "minimum": 0,
+  "type": "number"
+}

addedInput schema / properties / storage_type

Added value: +{
+  "description": "storage type; accepted values: ssd, nvme, hdd, network.",
+  "enum": [
+    "ssd",
+    "nvme",
+    "hdd",
+    "network"
+  ],
+  "examples": [
+    "ssd"
+  ],
+  "type": "string"
+}

addedInput schema / properties / table_pages

Added value: +{
+  "description": "table pages used by this deterministic tool.",
+  "examples": [
+    1
+  ],
+  "minimum": 1,
+  "type": "number"
+}

addedInput schema / properties / table_rows

Added value: +{
+  "description": "table rows used by this deterministic tool.",
+  "examples": [
+    1
+  ],
+  "minimum": 1,
+  "type": "number"
+}

changedInput schema / required

Previous value: -[
-  "query"
-]New value: +[
+  "table_rows",
+  "table_pages",
+  "selectivity_pct",
+  "storage_type"
+]

removedOutput schema / properties / cost_level
```
Removed value: -{
-  "type": "string"
-}
```
addedOutput schema / properties / cost_ratio
```
Added value: +{
+  "type": "number"
+}
```
removedOutput schema / properties / cost_score
```
Removed value: -{
-  "type": "number"
-}
```
addedOutput schema / properties / index_pages
```
Added value: +{
+  "type": "number"
+}
```
addedOutput schema / properties / index_scan_cost
```
Added value: +{
+  "type": "number"
+}
```
addedOutput schema / properties / index_tuples
```
Added value: +{
+  "type": "number"
+}
```
addedOutput schema / properties / random_page_cost
```
Added value: +{
+  "type": "number"
+}
```
addedOutput schema / properties / recommended_plan
```
Added value: +{
+  "type": "string"
+}
```
addedOutput schema / properties / sequential_scan_cost
```
Added value: +{
+  "type": "number"
+}
```
removedOutput schema / properties / warning_count
```
Removed value: -{
-  "type": "number"
-}
```

removedOutput schema / properties / warnings

Removed value: -{
-  "items": {
-    "type": "string"
-  },
-  "type": "array"
-}

changedOutput schema / required

Previous value: -[
-  "computation_basis",
-  "cost_level",
-  "cost_score",
-  "interpretation",
-  "next_step",
-  "next_step_url",
-  "warning_count",
-  "warnings",
-  "why_follow_up"
-]New value: +[
+  "computation_basis",
+  "cost_ratio",
+  "index_pages",
+  "index_scan_cost",
+  "index_tuples",
+  "interpretation",
+  "next_step",
+  "next_step_url",
+  "random_page_cost",
+  "recommended_plan",
+  "sequential_scan_cost",
+  "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"
+    },
+    "computation_basis": {
+      "type": "string"
+    },
+    "cost_level": {
+      "type": "string"
+    },
+    "cost_score": {
+      "type": "number"
+    },
+    "interpretation": {
+      "type": "string"
+    },
+    "next_step": {
+      "type": "string"
+    },
+    "next_step_url": {
+      "type": "string"
+    },
+    "warning_count": {
+      "type": "number"
+    },
+    "warnings": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "why_follow_up": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "computation_basis",
+    "cost_level",
+    "cost_score",
+    "interpretation",
+    "next_step",
+    "next_step_url",
+    "warning_count",
+    "warnings",
+    "why_follow_up"
+  ],
+  "type": "object"
+}

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

TDQS

B3.2/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false, and destructiveHint=false, so the safe deterministic profile is covered. The description adds that this is a pure estimate using a known four-input model, consistent with the annotations, but adds no extra behavioral context beyond that.

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 sentences, front-loaded with the operation and its inputs, with no padding. The trailing sentence about the browser calculator is mildly useful context rather than filler.

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

Completeness4/5

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 need not be explained, and annotations carry the safety profile. For a deterministic estimator with fully documented parameters, the description is complete enough, though a note on the underlying cost model would add value.

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 four parameters (table_rows, table_pages, selectivity_pct, storage_type) are already documented, including the storage_type enum. The description only restates the input list without adding syntax or modeling detail, so the baseline 3 applies.

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 (Estimate) and a precise resource (PostgreSQL sequential-scan and index-scan cost), then names the four inputs. It is clearly distinguishable from sibling cost calculators (ec2-cost-calculator, terraform-plan-cost-estimator) though it does not explicitly contrast itself with them.

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

Usage Guidelines2/5

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

There is no explicit when-to-use, when-not-to-use, or alternative-tool guidance. The reference to 'the same four-input model as the browser calculator' gives context about consistency but tells the agent nothing about when this tool is the right pick.

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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