Learn to Budget a Free Model Tier by Building a Tiny Token Ledger

Core point: a free model tier is not a yes/no answer; it is a budget. Before I send a batch job to an advertised free tier, I want a deterministic ledger that predicts a quota miss instead of discovering it after 40 minutes. Disclosure: This article was prepared as part of MonkeyCode's product outreach. Recent DEV threads circle around AI watermarking, agent tool gates, and whether AI is a thinking problem. My problem is smaller: I have an operator-supplied figure of 30,000,000 free tokens and a free server option , and I want to know if a batch script fits without making a single live request. Why this matters now Free tiers tend to advertise a raw allowance, but batch jobs fail in unhelpful ways: The counter jumps at the end, not before the job. A retry doubles the spend without visible feedback. System prompts, long completions, and JSON overhead count too. A tiny ledger turns that into a pass/fail fixture before any API call. The failing fixture Suppose a batch job needs 6,000 summaries where each prompt is roughly 21,000 characters. The completion target is 500 characters per call. My rough English heuristic is: 1 token ≈ 4 characters That gives 5,250 prompt tokens plus 125 completion tokens per call, so 5,375 tokens per call. Multiplied by 6,000 calls, the job would need about 32,250,000 tokens — over the 30,000,000 allowance. That is the error input. The job must fail before I spend anything. The minimal ledger Python 3.11+ is enough. No external packages. Replace the ALLOWANCE value with the limit from your own account. from dataclasses import dataclass ALLOWANCE = 30_000_000 # operator-supplied allowance, 30M tokens @dataclass ( frozen = True ) class Job : name : str prompt_chars : int completion_chars : int calls : int def estimate_tokens ( chars : int ) -> int : # Planning heuristic only: 1 English token ~= 4 characters. # A real tokenizer will differ; use it for order-of-magnitude checks. return max ( 1 , chars // 4 ) def plan_job ( job : Job , allowance