Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add terrylica/cc-skills --skill asciinema-cast-formatgit clone --depth 1 https://github.com/terrylica/cc-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/terrylica/cc-skills/asciinema-cast-format)<a href="https://agentmods.dev/skills/terrylica/cc-skills/asciinema-cast-format"><img src="https://agentmods.dev/badge/skills/terrylica/cc-skills/asciinema-cast-format/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/terrylica/cc-skills/asciinema-cast-format"><img src="https://agentmods.dev/badge/skills/terrylica/cc-skills/asciinema-cast-format.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Rogue Agent · line 251 Skill modifies its own code, configuration, or behavior at runtime. Self-modification enables an agent to escalate privileges, disable safety constraints, or install persistent backdoors.Fix: Prevent the skill from modifying its own code, SKILL.md, or configuration files. Treat skill files as read-only at runtime.
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00037 | $0.01970 |
| Opus 5 | $0.00018 | $0.00985 |
| Sonnet 5 | $0.00007 | $0.00394 |
| Haiku 4.5 | $0.00004 | $0.00197 |
Grade A, and why
asciinema-cast-format scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 11d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 254 lines — stays where its author put it; the contents beside it link to each section on GitHub.
asciinema-cast-format
Reference documentation for the asciinema v3 .cast file format (asciicast v2 specification).
Platform: All platforms (documentation only)
Self-Evolving Skill: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.
When to Use This Skill
Use this skill when:
- Parsing or inspecting .cast file structure
- Understanding NDJSON header and event formats
- Building tools that read or write .cast files
- Debugging recording issues or format errors
- Learning the asciicast v2 specification
Format Overview
Asciinema v3 uses NDJSON (Newline Delimited JSON) format:
- Line 1: Header object with recording metadata
- Lines 2+: Event arrays with timestamp, type, and data
Header Specification
The first line is a JSON object with these fields:
| Field | Type | Required | Description |
|---|---|---|---|
version |
int | Yes | Format version (always 2 for v3 recordings) |
width |
int | Yes | Terminal width in columns |
height |
int | Yes | Terminal height in rows |
timestamp |
int | No | Unix timestamp of recording start |
duration |
float | No | Total duration in seconds |
title |
string | No | Recording title |
env |
object | No | Environment variables (SHELL, TERM) |
theme |
object | No | Terminal color theme |
Example Header
{
"version": 2,
"width": 120,
"height": 40,
"timestamp": 1703462400,
"duration": 3600.5,
"title": "Claude Code Session",
"env": { "SHELL": "/bin/zsh", "TERM": "xterm-256color" }
}
Event Codes
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 11d ago First seen · 254 lines · 37 tokens per session scan A 0dee628c6dad
asciinema-cast-format is a skill published in the GitHub repository terrylica/cc-skills (72 stars, last pushed yesterday), licensed MIT. It adds 37 tokens to every session and 1,970 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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