AI Rate Card

subscription_vs_api

Read-only

Is a chat subscription (e.g. Claude Pro) cheaper than the same use through the API? Messages a day and tokens per message priced at the cheapest real-time seller of a model and at the maker's own API, a month of 30 days, against the subscription's price, with the break-even messages a day. USD. preset claude-pro / mistral-pro takes the plan price from our plan tables; otherwise pass price.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "subscription_vs_api"
  }
}

Input Schema

Name	Required	Description
`model`	No	model id; default the preset's model (claude-pro: anthropic/claude-sonnet-5-5)
`price`	No	subscription USD a month, when no preset
`preset`	No	a plan we collect the price of
`input_tokens`	No	per message incl. the resent chat, default 3000
`output_tokens`	No	per message, default 600
`messages_per_day`	No	default 40

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 8, 2026

TDQS

A3.8/5.0

Behavior4/5

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

readOnlyHint=true already covers the safety profile, so this is bonus context: the description discloses the 30-day month assumption, the currency (USD), that prices come from cheapest real-time sellers versus the maker's own API, and that a break-even figure is produced. It does not describe pagination or response shape, but no output schema exists and the key behavioral assumptions are stated.

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 with no filler, and the decision question is front-loaded ahead of mechanism and currency. The second sentence is a dense run-on with elliptical phrasing ('a month of 30 days, against the subscription's price'), which costs some readability but not much length.

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?

All six parameters are optional with defaults documented in the schema, and the description supplies the interpretive frame (subscription price source, 30-day month, USD, break-even output). Return values are not explained, but the central output -- break-even messages a day -- is named, which is sufficient for a read-only calculator without an output schema.

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 coverage is 100%, so the baseline would be 3, but the description adds meaning the schema does not: the preset path pulls the plan price from internal plan tables while the non-preset path requires an explicit price, and the day/token inputs are framed as per-message consumption over a 30-day month. That resolves the practical ambiguity in how price, preset, and the token counts interact.

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 opening question states the exact comparison -- chat subscription cost versus the same workload through the API -- with the mechanism (cheapest real-time seller price vs maker's own API) and the deliverable (break-even messages a day). It is distinguishable from costing siblings such as estimate_cost or cheapest_for_workload, though the telegraphic phrasing takes a second read.

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?

Usage is implied by the question framing (buying decision for a chat plan), and the preset/price rule tells the agent which path to take when the plan is one of the collected tables. However, it never says when to prefer this over estimate_cost or cheapest_for_workload for a combined subscription-plus-API comparison.

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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