Rahul D Sarker: Marketing & RevOps Tools

SaaS Churn Cohort Visualizer

saas_churn_cohort_visualizer

Read-onlyIdempotent

Project how a customer cohort decays over time under a monthly churn rate, and the implied average customer lifespan. See the full version at https://rahuldsarker.co/calculators/saas-churn-cohort-visualizer

Input Schema

TableJSON Schema

Name	Required	Description
`segment`	No	Customer segment for the benchmark verdict: smb, mid_market or enterprise (default smb)
`currency`	No	ISO 4217 code for money in the result, e.g. "USD", "INR", "EUR", "GBP". Omit to show plain numbers.
`cohortSize`	Yes	Starting cohort size (number of customers)
`monthlyChurnPct`	Yes	Monthly logo churn rate, as a percentage

Output Schema

TableJSON Schema

Name	Required	Description
`url`	Yes
`kind`	Yes
`tool`	Yes	The calculator tool that produced this result
`notes`	Yes
`title`	Yes
`inputs`	Yes
`compact`	Yes
`metrics`	Yes	Every "Label: value" line of the result; value is the first number on the line
`currency`	Yes
`benchmarks`	Yes	Rule-of-thumb verdicts for the headline numbers
`bookingUrl`	Yes
`calculator`	Yes	Slug of the interactive calculator on rahuldsarker.co

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedSep 30, 2026

addedInput schema / properties / currency

Added value: +{
+  "description": "ISO 4217 code for money in the result, e.g. \"USD\", \"INR\", \"EUR\", \"GBP\". Omit to show plain numbers.",
+  "pattern": "^[A-Za-z]{3}$",
+  "type": "string"
+}

addedInput schema / properties / segment

Added value: +{
+  "description": "Customer segment for the benchmark verdict: smb, mid_market or enterprise (default smb)",
+  "enum": [
+    "smb",
+    "mid_market",
+    "enterprise"
+  ],
+  "type": "string"
+}

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "additionalProperties": false,
+  "properties": {
+    "benchmarks": {
+      "description": "Rule-of-thumb verdicts for the headline numbers",
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "band": {
+            "type": "string"
+          },
+          "display": {
+            "type": "string"
+          },
+          "metric": {
+            "type": "string"
+          },
+          "name": {
+            "type": "string"
+          },
+          "read": {
+            "type": "string"
+          },
+          "segment": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "source": {
+            "type": "string"
+          },
+          "target": {
+            "type": "string"
+          },
+          "tone": {
+            "enum": [
+              "good",
+              "ok",
+              "warn",
+              "bad"
+            ],
+            "type": "string"
+          },
+          "value": {
+            "type": "number"
+          }
+        },
+        "required": [
+          "metric",
+          "name",
+          "value",
+          "display",
+          "band",
+          "tone",
+          "read",
+          "target",
+          "segment",
+          "source"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "bookingUrl": {
+      "type": "string"
+    },
+    "calculator": {
+      "description": "Slug of the interactive calculator on rahuldsarker.co",
+      "type": "string"
+    },
+    "compact": {
+      "type": "boolean"
+    },
+    "currency": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "inputs": {
+      "additionalProperties": {},
+      "propertyNames": {
+        "type": "string"
+      },
+      "type": "object"
+    },
+    "kind": {
+      "const": "calculator",
+      "type": "string"
+    },
+    "metrics": {
+      "description": "Every \"Label: value\" line of the result; value is the first number on the line",
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "display": {
+            "type": "string"
+          },
+          "label": {
+            "type": "string"
+          },
+          "unit": {
+            "anyOf": [
+              {
+                "enum": [
+                  "currency",
+                  "x",
+                  "%",
+                  "months"
+                ],
+                "type": "string"
+              },
+              {
+                "type": "null"
+              }
+            ]
+          },
+          "value": {
+            "type": [
+              "number",
+              "null"
+            ]
+          }
+        },
+        "required": [
+          "label",
+          "value",
+          "unit",
+          "display"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "notes": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "title": {
+      "type": "string"
+    },
+    "tool": {
+      "description": "The calculator tool that produced this result",
+      "type": "string"
+    },
+    "url": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "kind",
+    "tool",
+    "title",
+    "calculator",
+    "url",
+    "bookingUrl",
+    "currency",
+    "compact",
+    "inputs",
+    "metrics",
+    "notes",
+    "benchmarks"
+  ],
+  "type": "object"
+}

First observedSep 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, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds useful context about what is being projected (cohort decay and average customer lifespan), but does not add behavioral details beyond annotations, such as output format or calculation constraints.

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 description is two sentences and front-loads the core purpose efficiently. The URL to the full version is slightly extraneous for an agent invocation but does not significantly detract from conciseness.

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?

Given that an output schema exists and schema coverage for parameters is 100%, the description does not need to explain return values or parameter details. It adequately conveys the tool's purpose for a read-only calculator, though it could mention the optional segment and currency parameters to be fully self-contained.

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 are already documented in the input schema. The description mentions monthly churn rate generically but adds no parameter-specific meaning beyond the schema, making the baseline of 3 appropriate.

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?

The description states a specific action (project cohort decay over time) and resource (customer cohort, monthly churn rate, implied average lifespan). It is clear what the tool computes, but it does not explicitly differentiate itself from similar calculation siblings like ltv_cac_calculator or net_revenue_retention_forecaster.

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?

The description only explains what the tool does, with no guidance on when to use it versus alternatives. It does not name any sibling tool or specify conditions or exclusions for invocation.

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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