Context Tax

Context Tax Calculator

Retrospectively classifies every turn in the current Claude Code session into five categories — four flavors of "context work" plus actual feature work — then estimates the time and tokens spent on each. The output is a breakdown report that helps the user see exactly what a session cost them beyond building the feature they sat down to build.

Why this matters

Every new Claude Code session starts cold. The user carries context in their head, retypes it, paraphrases it, and corrects Claude when it misremembers or reinvents things. That work is invisible in the moment — it just feels like "coding" — but it's a tax on the session. Measuring it once gives the user the number they need to decide whether persistent project documentation is worth the setup cost.

Numbers from this skill are approximations, not exact measurements. Classification is heuristic and will occasionally miscategorize borderline turns. That's fine — the goal is a roughly accurate breakdown that reveals which category dominates, not a precise audit.

When to Use

• User invokes /context-tax at the end of a coding session
• User asks to "calculate the context tax", "show me my context tax", "how much did I spend on context this session", "audit this session", or similar phrasings about session efficiency
• User is about to close the terminal and wants a post-mortem of the session they just completed

Run this skill BEFORE the session ends — once the transcript is closed, the in-context conversation disappears and only the JSONL file remains.

Procedure

Step 1: Locate the session transcript

Primary source: the JSONL file at ~/.claude/projects/<slug>/<session-id>.jsonl where <slug> is the current working directory with / replaced by - (e.g., /home/alice/projects/myapp becomes -home-alice-projects-myapp).

# Find the most recent session file for this project
ls -t ~/.claude/projects/"$(pwd | sed 's|/|-|g')"/*.jsonl 2>/dev/null | head -1

If the JSONL isn't readable (permissions, not yet flushed, or the user is not in Claude Code), fall back to analyzing the conversation visible in the current context window. The JSONL is preferred because it contains precise token counts and timestamps per turn.

Step 2: Classify each turn

For each USER turn, pick exactly one category based on the dominant content. When a turn mixes categories, pick the one the user spent the most words on.

For each ASSISTANT turn, classify by dominant activity:

• Re-reading CLAUDE.md, rule files, or style guide references → style_guide
• Searching for existing utilities, reading the project structure, exploring files for orientation → codebase_explanation
• Writing new feature code, fixing bugs, running tests, debugging → feature_work
• Re-explaining an approach or walking the user through an alternative because the prior approach was rejected → ways_of_doing_things
• Rewriting code that duplicated an existing utility, after being corrected → reinvented_wheel_fix

When a turn is ambiguous, classify as feature_work — we want a conservative tax estimate, not an inflated one.

Step 3: Estimate time and tokens per turn

Tokens (preferred — from JSONL):

Each JSONL entry has message.usage.input_tokens and message.usage.output_tokens. Sum both for the turn's token cost.

Tokens (fallback — from in-context conversation):

Estimate at 4 characters per token. Count total characters in the turn (user message or assistant response) and divide by 4. When using this fallback, prefix the Tokens column in the final report with `` to signal approximation.

Time (preferred — from JSONL timestamps):

Each JSONL entry has a timestamp field. Compute the time between consecutive turns and attribute it to the earlier turn (this captures user thinking time + assistant response time).

Time (fallback — when timestamps are unavailable):

• Assistant turns: assume 200 tokens/second output rate
• User turns: assume 40 words/minute typing rate

Step 4: Identify the top 3 costliest context moments

Across all non-feature_work turns, rank by individual-turn time spent and pick the top 3. For each, capture a short quote (first 12 words) or a summary of what the turn was about. Skip this section entirely if the session has fewer than 5 turns — the sample is too small to be meaningful.

Step 5: Render the report

Output this exact markdown structure, filling in the bracketed values:

# Context Tax Report — [YYYY-MM-DD HH:MM]

**Total session**: [X] minutes · [Y] tokens

## Breakdown

| Category               | Time    | Tokens  | % of session |
| ---------------------- | ------- | ------- | ------------ |
| Codebase explanation   | [X] min | [Y] tok | [Z]%         |
| Style guide            | [X] min | [Y] tok | [Z]%         |
| Ways of doing things   | [X] min | [Y] tok | [Z]%         |
| Reinvented-wheel fixes | [X] min | [Y] tok | [Z]%         |
| **Feature work**       | [X] min | [Y] tok | [Z]%         |

**Context tax**: [100 minus feature_work %]% of this session went to
context, not features.

## Top 3 costliest context moments

1. **[Category]** — [X] min — "[short quote or summary]"
2. **[Category]** — [X] min — "[short quote or summary]"
3. **[Category]** — [X] min — "[short quote or summary]"

## The fix

If your context tax is above 20%, persist this context so you don't pay
it again next session. Create three files in your project root:

- `PROJECT.md` — the "why" (stack decisions, constraints, non-goals)
- `ROADMAP.md` — the "what" (phases, current status)
- `STATE.md` — the "where" (cursor: which phase/task you stopped on)

Then add a Session Protocol to your `CLAUDE.md` that reads all three
files on session start and updates STATE.md on session end. The first
run of `/context-tax` after adopting persistent context usually drops
by 20-40 percentage points.

Output Conventions

• Always fill in real numbers — never leave [X] placeholders in the final output
• Round time to the nearest minute; if a category is under 1 minute, show <1 min
• Round token counts to the nearest 100 if above 1000 (e.g., 12.3k tok)
• Round percentages to whole numbers
• When feature_work is above 80%, add a closing line: "Most of this session went to features — nice work." Skip the "fix" section in that case since the tax is already low
• Skip the "Top 3" section if the session has fewer than 5 turns
• When falling back to character-based token estimation, prefix the Tokens column header with ~ (e.g., ~Tokens) and add a single-line note at the bottom: "Tokens estimated from character counts — add the --jsonl flag or ensure session transcript access for precise numbers."

Examples

Input scenario (session has 18 turns, 45 minutes):

The user spent the first 10 minutes explaining their project structure, then 5 minutes correcting Claude's assumption about their style guide, then 25 minutes pair-programming a feature, then 5 minutes at the end because Claude built a duplicate of an existing helper.

Expected report:

# Context Tax Report — 2026-04-15 21:34

**Total session**: 45 minutes · 38.2k tokens

## Breakdown

| Category               | Time   | Tokens    | % of session |
| ---------------------- | ------ | --------- | ------------ |
| Codebase explanation   | 10 min | 8.5k tok  | 22%          |
| Style guide            | 5 min  | 4.1k tok  | 11%          |
| Ways of doing things   | <1 min | 0.3k tok  | 1%           |
| Reinvented-wheel fixes | 5 min  | 3.8k tok  | 11%          |
| **Feature work**       | 25 min | 21.5k tok | 55%          |

**Context tax**: 45% of this session went to context, not features.

## Top 3 costliest context moments

1. **codebase_explanation** — 6 min — "ok so the project structure is a
   monorepo with apps/ and packages/, and..."
2. **reinvented_wheel_fix** — 5 min — "no we already have formatDate in
   lib/utils/date.ts, please don't..."
3. **style_guide** — 3 min — "we don't use semicolons, check CLAUDE.md,
   also we prefer const over let..."

## The fix

If your context tax is above 20%, persist this context so you don't
pay it again next session. Create three files in your project root:

- `PROJECT.md` — the "why" (stack decisions, constraints, non-goals)
- `ROADMAP.md` — the "what" (phases, current status)
- `STATE.md` — the "where" (cursor: which phase/task you stopped on)

Then add a Session Protocol to your `CLAUDE.md` that reads all three
files on session start and updates STATE.md on session end. The first
run of `/context-tax` after adopting persistent context usually drops
by 20-40 percentage points.

Notes

• Classification is heuristic — borderline turns may be miscategorized, but the aggregate breakdown will still be directionally accurate
• The skill is designed for a single session at a time; don't attempt to aggregate across sessions unless the user explicitly asks
• If the user runs the skill twice in the same session, the second run will include the first run's output in the transcript; that's fine, it usually classifies as feature_work and doesn't skew results