Tools Howto
A 429 is free. The ninth retry is not.
A 429 bills you nothing - the request never reaches the model. The cost arrives when your backoff outlives the cache TTL and the cold retry burns 101x the limit.
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Tools & how-to.
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Concrete how-to guides for working with LLM APIs and tooling -- enabling prompt caching the right way, instrumenting cost telemetry, picking a model for a specific workload class. Each guide includes runnable code or commands, the exact vendor page that documents the API surface, and a date stamp that lets the reader judge how fresh the recipe is. We do not publish a how-to until it has been run against a live API at least once. The category opens empty in Phase D. The first guides will follow once the analysis catalogue covers the conceptual ground a how-to builds on.
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Tools Howto 02
input_tokens means three different things. Your cost function knows one of them.
Anthropic's input_tokens excludes cached tokens, OpenAI's includes them. Port a cost function between the two and a $0.082 request bills $0.378. Fields, traps, code.
Tools Howto 03
The 20x in Claude Code caching is real — it's a penalty, not a discount
A cache miss costs exactly 20x the warm read of the same history. What that does to your plan limits, which settings change it, and the number nobody can compute.
Tools Howto 04
The Batch API discount isn't 50% -- and it isn't always a discount
Batch halves token rates at OpenAI, Anthropic and Google -- but takes 20% at SpaceXAI and nothing on its flagship. When batch beats a warm cache, and when it costs more.
Tools Howto 05
How to actually get prompt cache hits (and why yours are missing)
Prompt caching fails silently -- no error, no warning, just a full-price bill. The floors, the breakpoint rules, and everything that quietly invalidates a cache.
Tools Howto 06
The context engineering playbook: which lever, in what order, and what each is worth
Five levers, one deployment order: which context feature to reach for by symptom, what each does to your cache and your bill, and one config that runs them all.
Tools Howto 07
The MCP context tax: how to stop paying for tools your agent never calls
Five MCP servers burn ~55k tokens before you ask anything. Tool search and programmatic tool calling (both now GA) cut that 85%+ — with one caveat that bites.
Tools Howto 08
Compaction: when to summarize an agent's history — and when it backfires
Anthropic's compaction API summarizes an agent's history when it hits a token threshold. How it works, the billing pass you don't see, and when it backfires.
Tools Howto 09
Context editing: cut agent token bills ~84% by clearing stale tool results
Anthropic's context editing clears stale tool results from an agent's window, cutting token use up to 84%. How it works, the config, and the prompt-cache catch.
Tools Howto 10
Caveman mode for Claude Code: the math behind the 65% headline
Caveman mode strips filler from Claude's output. The 65% headline is real for output tokens. Here's what it actually saves on your monthly bill.