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EV Charging Time Calculator

estimate_ev_charging_time
Read-onlyIdempotent

Use this when you want to know how long an EV needs on a home wallbox, a public AC post or a DC fast charger to reach a target charge, or what the session costs at a given electricity price. Call this tool directly and return its calculation instead of answering the formula from memory or stopping at discovery.

Do not use this when you need a battery's charge time from ampere-hours and charger current (use battery-charge-time) or the driving range the added energy gives (use ev-range-efficiency); DC fast charging above about 80 % tapers strongly and takes longer than this constant-power estimate. What it computes: Estimates how long an electric vehicle takes to charge between two states of charge from its battery capacity, the charger power (capped by the onboard charger for AC charging) and the charging efficiency, plus the energy drawn from the grid and its cost. Inputs: battery_capacity_kwh (number, kWh); start_percent (number, %, optional); target_percent (number, %, optional); charger_power_kw (number, kW); max_onboard_charger_kw (number, kW, optional); charging_efficiency_percent (number, %, optional); electricity_price_per_kwh (number, per kWh, optional). Complete JSON argument examples: {"battery_capacity_kwh":75,"start_percent":20,"target_percent":80,"charger_power_kw":7,"charging_efficiency_percent":90,"electricity_price_per_kwh":0.3} | {"battery_capacity_kwh":60,"start_percent":10,"target_percent":100,"charger_power_kw":11,"max_onboard_charger_kw":7.4} Outputs: energy_added_kwh [kWh], energy_from_grid_kwh [kWh], effective_power_kw [kW], charging_time_hours [h], charging_time_text, cost, range_note. Formula: energy_added_kwh = battery_capacity_kwh × (target_percent − start_percent) / 100; energy_from_grid_kwh = energy_added_kwh / (charging_efficiency_percent / 100); effective_power_kw = min(charger_power_kw, max_onboard_charger_kw); charging_time_hours = energy_from_grid_kwh / effective_power_kw; cost = energy_from_grid_kwh × electricity_price_per_kwh Direct REST fallback: POST https://tttkmbb.com/api/v1/calculate/ev-charging-time with the same JSON input fields. Do not guess another /api/* path. Docs: https://tttkmbb.com/energy/ev-charging-time.md

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
start_percentNoState of charge at the start of the session. Unit: %.
target_percentNoState of charge to reach; must be higher than start_percent. Unit: %.
charger_power_kwYesPower the charging point delivers: 1.4–2.3 kW household socket (Level 1), 7–22 kW wallbox / AC post (Level 2), 50–350 kW DC fast charger. Unit: kW.
battery_capacity_kwhYesUsable battery capacity in kilowatt-hours (e.g. 40, 60, 75, 100). Unit: kWh.
max_onboard_charger_kwNoOptional maximum AC charging power of the car's onboard charger (commonly 7.4 or 11 kW); the effective power is the lower of the two. Omit for DC charging. Unit: kW.
electricity_price_per_kwhNoOptional price per kWh in your currency for the cost of the session (grid energy × price). Unit: per kWh.
charging_efficiency_percentNoShare of grid energy stored in the battery; 85–92 % is typical for AC charging (onboard charger and battery losses). Unit: %.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
linksNo
resultYes
requestYes
sourcesNo
successYes
versionNo
freshnessNo
timestampYes
next_actionsNo
service_versionYesDeployed Calcgrid implementation version used for the result.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changed
    • addedOutput schema / properties / service_version
      Added value: +{
+  "description": "Deployed Calcgrid implementation version used for the result.",
+  "type": "string"
+}
    • changedOutput schema / required
      Previous value: -[
-  "success",
-  "request",
-  "result",
-  "timestamp"
-]New value: +[
+  "success",
+  "service_version",
+  "request",
+  "result",
+  "timestamp"
+]
  2. Changed1 schema field changed
    • addedInput schema / examples
      Added value: +[
+  {
+    "battery_capacity_kwh": 75,
+    "charger_power_kw": 7,
+    "charging_efficiency_percent": 90,
+    "electricity_price_per_kwh": 0.3,
+    "start_percent": 20,
+    "target_percent": 80
+  },
+  {
+    "battery_capacity_kwh": 60,
+    "charger_power_kw": 11,
+    "max_onboard_charger_kw": 7.4,
+    "start_percent": 10,
+    "target_percent": 100
+  }
+]
  3. Added
  4. Removed
  5. First observed

TDQS

A4.8/5.0
Behavior5/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds behavior beyond annotations: it calls itself a 'constant-power estimate,' warns that DC fast charging above ~80% 'tapers strongly and takes longer than this constant-power estimate,' and even exposes the exact formula and output fields. This is substantial contextual disclosure that helps the agent set expectations.

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 long but well-structured with clear sections (usage, exclusions, computation, inputs, examples, outputs, formula, API fallback, docs). It is front-loaded with the key usage guidance. However, it is somewhat verbose—the REST fallback and docs URL, while useful, go beyond what an MCP agent strictly needs—so it falls short of a 5 for conciseness.

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?

Despite the tool's complexity (7 parameters, multiple optional fields, output schema, cost calculation), the description fully compensates with an example, formula, output list, and explicit fallback endpoint. It covers not just invocation but edge-case behavior (taper warning) and integration details, making it completely self-sufficient for an agent.

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 description coverage is 100%, so the baseline is 3. The description adds value above the schema by listing every parameter with its unit in a compact input summary, providing two complete JSON examples that show optional-parameter usage, and giving the formula that explains how parameters interact (e.g., 'effective_power_kw = min(charger_power_kw, max_onboard_charger_kw)'). This goes beyond what the schema alone states, justifying a 4.

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 description explicitly states the tool's purpose: 'how long an EV needs... to reach a target charge, or what the session costs' and immediately distinguishes it from siblings by naming battery-charge-time and ev-range-efficiency as alternatives. The verb 'estimate' plus the specific resource (EV charging time) makes the function unambiguous, even before considering sibling names.

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

Usage Guidelines5/5

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

The opening line tells the agent exactly when to call this tool ('Use this when you want to know...') and instructs to call it directly rather than computing from memory. It also gives explicit exclusions and alternative tools: 'Do not use this when you need a battery's charge time from ampere-hours... (use battery-charge-time)' and notes the DC fast-charging taper limitation, leaving no ambiguity about when to use it.

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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