Engineering guides and deep dives on Claude - short how-tos and long-form breakdowns.
One rule, three layers, measured: a rule in Claude Code's auto memory held 3/3 runs until the user contradicted it, then failed 0/3 - the same score the identical rule got in CLAUDE.md.
Opus 5 ships at the same $5/$25 as Opus 4.8 with near-Fable agentic quality - more than double Opus 4.8 on Frontier-Bench, within 0.5% of Fable on CursorBench at half the cost per task - so escalate to Fable only when the peak or the refusal surface is worth it.
OS-level Bash sandboxing cut Anthropic's permission prompts ~84%, but /sandbox only wraps Bash. Pick the right isolation tier, deny credential reads, and lock managed settings for unattended work.
Channels are MCP servers that inject Telegram, Discord, iMessage, or webhook events into the local Claude Code session you already have open - v2.1.80+, `--channels` per session, and a sender allowlist, not just `.mcp.json`.
A practical map of Claude Code’s shortcuts, prefixes, session commands, and CLI flags - ordered like a real terminal cheatsheet.
Claude Code ships 42 built-in tools and only 13 ask for permission - the read/mutate split, gotchas for the tools you touch daily, and the ToolName(specifier) rules that restrict or disable any of them.
Fable 5 ships GA at $10/$50 per million tokens with a 1M context - and safety classifiers that return refusals as HTTP 200 responses, so every integration needs refusal handling, a fallback path, and new billing rules.
/goal sets a completion condition and Claude keeps taking turns until a separate small fast model (default Haiku) confirms it from the transcript. Requires v2.1.139+, one goal per session, condition up to 4,000 characters.
Plan mode makes Claude Code read and plan without touching disk until you approve - enable it with Shift+Tab or --permission-mode plan. Under the hood it's prompt reinforcement plus a markdown plan file, not a hard tool lockdown.
Claude Code runs a gather→act→verify loop: startup load fills context before you type, then file reads and tool output pile up as the loop runs - compaction, /clear, and subagents are the official levers for what sticks.
Fable 5 escalates for the hardest reasoning, Opus 5 orchestrates near Fable at half the price, Sonnet 5 is the default worker, Haiku 4.5 does the parallel grunt work. Choose by the job and the token bill, not the benchmark.
Sonnet 5 ships as the default on Free and Pro with intro API pricing at $2/$10 per million tokens - near Opus 5 on agentic benchmarks at 40% of Opus input cost through the 2026-08-31 intro window (60% at standard pricing) when you keep effort at Medium or below.
Claude Code runs up to a 1M-token window on flagship models, but a bigger window doesn't fix a cluttered one - every turn replays the whole history and quality drops before the cap.
A bloated CLAUDE.md gets filtered out as noise. Keep it to universal instructions and move everything else behind progressive disclosure.