节省

PRECC追踪每次拦截的估计token节省。使用 precc savings 查看PRECC阻止了多少浪费。

快速摘要

$ precc savings
Session Token Savings
=====================
Total estimated savings: <span data-stat="session_tokens_saved">8,741</span> tokens

Breakdown:
  Pillar 1 (cd prepends):         <span data-stat="session_p1_tokens">3,204</span> tokens  (<span data-stat="session_p1_count">6</span> corrections)
  Pillar 4 (skill activations):   <span data-stat="session_p4_tokens">1,560</span> tokens  (<span data-stat="session_p4_count">4</span> activations)
  RTK rewrites:                   <span data-stat="session_rtk_tokens">2,749</span> tokens  (<span data-stat="session_rtk_count">11</span> rewrites)
  Lean-ctx wraps:                 <span data-stat="session_lean_tokens">1,228</span> tokens  (<span data-stat="session_lean_count">2</span> wraps)

详细分类（Pro）

$ precc savings --all
Session Token Savings (Detailed)
================================
Total estimated savings: <span data-stat="session_tokens_saved">8,741</span> tokens

Command-by-command:
  #  Time   Command                          Saving   Source
  1  09:12  cargo build                      534 tk   cd prepend (cargo-wrong-dir)
  2  09:14  cargo test                       534 tk   cd prepend (cargo-wrong-dir)
  3  09:15  git status                       412 tk   cd prepend (git-wrong-dir)
  4  09:18  npm install                      824 tk   cd prepend (npm-wrong-dir)
  5  09:22  find . -name "*.rs"              387 tk   RTK rewrite (output truncation)
  6  09:25  cat src/main.rs                  249 tk   RTK rewrite (lean-ctx wrap)
  7  09:31  cargo clippy                     534 tk   cd prepend (cargo-wrong-dir)
  ...

Pillar Breakdown:
  Pillar 1 (context resolution):   <span data-stat="session_p1_tokens">3,204</span> tokens  <span data-stat="session_p1_pct">36.6</span>%
  Pillar 2 (GDB debugging):            0 tokens   0.0%
  Pillar 3 (mined preventions):        0 tokens   0.0%
  Pillar 4 (automation skills):    <span data-stat="session_p4_tokens">1,560</span> tokens  <span data-stat="session_p4_pct">17.8</span>%
  RTK rewrites:                    <span data-stat="session_rtk_tokens">2,749</span> tokens  <span data-stat="session_rtk_pct">31.5</span>%
  Lean-ctx wraps:                  <span data-stat="session_lean_tokens">1,228</span> tokens  <span data-stat="session_lean_pct">14.1</span>%

如何估算节省

每种修正类型都有基于没有PRECC时会发生什么的估计token成本：

这些是保守估计。实际节省通常更高，因为Claude对错误的推理可能很冗长。

累计节省

节省数据在PRECC数据库中跨会话持久化。随着时间推移，您可以跟踪总体影响：

$ precc savings
Session Token Savings
=====================
Total estimated savings: <span data-stat="session_tokens_saved">8,741</span> tokens

Lifetime savings: <span data-stat="total_tokens_saved">142,389</span> tokens across <span data-stat="total_sessions">47</span> sessions

Status Bar

After installation, PRECC wires a statusLine entry into ~/.claude/settings.json so the Claude Code status bar shows live session metrics:

$0.42 spent | 1.2M in/out | 📊 last cmd: −1.2K | PRECC: 7 fixes | 5.8ms avg | this session: 320 saved over 7 cmds (~$0.05) | lifetime: 8.9K saved over 217 cmds (~$2.85)

Each segment:

The lifetime: segment is placed last so it’s the first to be truncated if Claude Code’s UI clips the bar at the right edge.

Why cost and token count don’t divide

The displayed 1.2M in/out is not the denominator that produced $0.42 spent. Claude Code’s cost.total_cost_usd is computed from the API’s full token breakdown — base input, output, plus cache reads and cache creations. The session-wide cumulative cache token counts are not exposed in the statusline schema, so PRECC can only show the visible (non-cache) portion.

On long sessions with heavy file rereads, cache reads can be 10× the visible token count. That’s why pairing the two as a ratio would mislead — PRECC shows them as independent segments instead.

Why PRECC doesn’t compute the cost

The cost number is authoritative. PRECC reads cost.total_cost_usd verbatim from the JSON Claude Code pipes into the status command on stdin. That’s the same number Claude Code charges against your subscription/usage budget. You can verify it any time with the built-in /cost slash command — both should agree.

What drives the cost

For Claude Opus 4.6:

The biggest drivers on long sessions are usually:

1. Output tokens — most expensive per-token type, especially on the 1M context tier
2. Repeated cache reads — cheap individually but accumulate fast across many turns
3. Cache creations — written once per file read, ~1.25× the base input rate

PRECC reduces the visible-token cost by compressing Bash output (the 📊 last cmd: segment shows the per-command saving), but it cannot reduce cache reads of files Claude has already loaded.

Stable session counts

The “PRECC: N fixes” segment counts events since the persisted session start, written to ~/.local/share/precc/sessions/<session_id>.start on the first statusline refresh of each session. This makes the count monotonic — it cannot drop mid-session even if cost.total_duration_ms is missing on a particular refresh (which would otherwise collapse the window to “since now” and silently drop nearly all events).

Auto-refreshed lifetime snapshot

The lifetime: segment reads ~/.local/share/precc/.lifetime_summary.json, which is rewritten:

• On every PostToolUse measurement (so it stays current as commands accumulate)
• On every precc savings invocation

The this session: segment reads the same lifetime file but subtracts a per-session baseline persisted to ~/.local/share/precc/sessions/<session_id>.savings_baseline on the first refresh of each session.

No need to manually refresh anything — the files update themselves.

Suppressing the status bar

If you’d rather keep your existing status bar, set your own statusLine command in ~/.claude/settings.json. PRECC’s installer will detect the custom value and leave it alone on subsequent updates.

To suppress only the per-interaction 📊 PRECC line (in additionalContext), set PRECC_QUIET=1 in your shell environment.