How do I install the Capture skill?

Run npx skillmds@latest add zapgun-ai/capture in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Capture safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Capture?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Capture free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Capture?

zapgun-ai (@zapgun-ai) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Capture by zapgun-ai — Agent Skill

Name: Capture
Author: zapgun-ai

Capture

Capture a REAL Claude Code /v1/messages body as a replay fixture, so the HTTP replay arm (.skills/replay) faithfully reproduces Claude Code's cache_control breakpoint structure (a hand-authored fixture makes the 1h-TTL knob look like a no-op). Starts a clawback proxy with --capture-body, drives ONE real claude turn through it via the PTY driver, verifies the dump carries cache_control breakpoints, and promotes it to the fixture path. Spends real Anthropic tokens (exactly one turn; pin a cheap model with --model). Use once before replay-based benchmarking, or to refresh the fixture when Claude Code changes its request shape.

zapgun-ai f01595f 2 files · 8.3 KB Updated Sep 17, 2026

File contents

clawback fixture capture

Run .skills/capture/scripts/capture_fixture.sh from the project root. It captures the genuine Claude Code request body end to end:

starts a standalone clawback proxy with --capture-body <tmp> (detached, via .skills/monitor's run_monitor.sh --detach);
drives one real claude turn through it (benchmark/bin/drive_pty.js --turns 1), which points claude at the proxy and types a single prompt;
stops the proxy;
verifies the dump with benchmark/bin/verify_fixture.js (must carry ≥1 cache_control breakpoint, else the 1h-TTL arm is a no-op);
promotes the temp dump to the fixture path at mode 0600.

The captured bytes are the request body only — system prompt, tools, and the one message. The Anthropic API key is not captured (it rides in headers clawback never dumps). Still, treat the fixture as sensitive: it contains your system prompt and tool definitions. It is gitignored-by-convention and excluded from the npm tarball.

Spends real tokens

Step 2 runs the real claude binary against your own Anthropic limits — exactly one turn. Pin a cheap model to keep it trivial:

.skills/capture/scripts/capture_fixture.sh --model claude-haiku-4-5-20251001

Requirements: the claude CLI on PATH, node-pty installed (npm i node-pty), and claude already authenticated.

Usage

# default: capture to benchmark/fixtures/ccode.json on 127.0.0.1:8787
.skills/capture/scripts/capture_fixture.sh --model claude-haiku-4-5-20251001

# custom destination / port / prompt:
.skills/capture/scripts/capture_fixture.sh --out benchmark/fixtures/mywork.json \
  --port 8790 --prompt "Summarize README.md in one line."

Options

--out PATH — fixture destination (default benchmark/fixtures/ccode.json).
--host, --port — proxy bind (default 127.0.0.1:8787).
--model ID — pin claude's model (cost control; forwarded to drive_pty).
--prompt TEXT — the single prompt to type (default: a read-only listing).
--keep-tmp — keep the temp dump even if verification fails (debugging).
everything after -- is forwarded to drive_pty.js.

Why this exists

--capture-body (in src/server.js) dumps the pristine body once, before clawback's strip/1h-rewrite mutations — so the fixture is exactly what Claude Code put on the wire. Replaying it through clawback then exercises the real cache mechanic. See .skills/replay.

After capture

Replay the fixture with .skills/replay, then analyze with .skills/bench and visualize with .skills/plot. For the faithful (non-replay) arm that drives real claude live, see .skills/drive.

---name: capturedescription: Capture a REAL Claude Code /v1/messages body as a replay fixture, so the HTTP replay arm (.skills/replay) faithfully reproduces Claude Code's cache_control breakpoint structure (a hand-authored fixture makes the 1h-TTL knob look like a no-op). Starts a clawback proxy with --capture-body, drives ONE real claude turn through it via the PTY driver, verifies the dump carries cache_control breakpoints, and promotes it to the fixture path. Spends real Anthropic tokens (exactly one turn; pin a cheap model with --model). Use once before replay-based benchmarking, or to refresh the fixture when Claude Code changes its request shape.---# clawback fixture captureRun `.skills/capture/scripts/capture_fixture.sh` from the project root. It captures thegenuine Claude Code request body end to end:1. starts a standalone clawback proxy with `--capture-body <tmp>` (detached, via `.skills/monitor`'s `run_monitor.sh --detach`);2. drives **one** real `claude` turn through it (`benchmark/bin/drive_pty.js --turns 1`), which points claude at the proxy and types a single prompt;3. stops the proxy;4. verifies the dump with `benchmark/bin/verify_fixture.js` (must carry ≥1 `cache_control` breakpoint, else the 1h-TTL arm is a no-op);5. promotes the temp dump to the fixture path at mode 0600.The captured bytes are the request body only — system prompt, tools, and theone message. The Anthropic API key is **not** captured (it rides in headersclawback never dumps). Still, treat the fixture as sensitive: it contains yoursystem prompt and tool definitions. It is gitignored-by-convention and excludedfrom the npm tarball.## Spends real tokensStep 2 runs the real `claude` binary against your own Anthropic limits —exactly one turn. Pin a cheap model to keep it trivial:```bash.skills/capture/scripts/capture_fixture.sh --model claude-haiku-4-5-20251001```Requirements: the `claude` CLI on PATH, `node-pty` installed (`npm inode-pty`), and claude already authenticated.## Usage```bash# default: capture to benchmark/fixtures/ccode.json on 127.0.0.1:8787.skills/capture/scripts/capture_fixture.sh --model claude-haiku-4-5-20251001# custom destination / port / prompt:.skills/capture/scripts/capture_fixture.sh --out benchmark/fixtures/mywork.json \ --port 8790 --prompt "Summarize README.md in one line."```## Options- `--out PATH` — fixture destination (default `benchmark/fixtures/ccode.json`).- `--host`, `--port` — proxy bind (default `127.0.0.1:8787`).- `--model ID` — pin claude's model (cost control; forwarded to drive_pty).- `--prompt TEXT` — the single prompt to type (default: a read-only listing).- `--keep-tmp` — keep the temp dump even if verification fails (debugging).- everything after `--` is forwarded to `drive_pty.js`.## Why this exists`--capture-body` (in `src/server.js`) dumps the **pristine** body once, beforeclawback's strip/1h-rewrite mutations — so the fixture is exactly whatClaude Code put on the wire. Replaying it through clawback then exercises thereal cache mechanic. See `.skills/replay`.## After captureReplay the fixture with `.skills/replay`, then analyze with `.skills/bench`and visualize with `.skills/plot`. For the faithful (non-replay) arm thatdrives real claude live, see `.skills/drive`.

Frequently asked questions