Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add xiaolai/echo-sleuth-for-claude/plugin install echo-sleuthWrote 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/xiaolai/echo-sleuth-for-claude/jsonl-core)<a href="https://agentmods.dev/skills/xiaolai/echo-sleuth-for-claude/jsonl-core"><img src="https://agentmods.dev/badge/skills/xiaolai/echo-sleuth-for-claude/jsonl-core.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00071 | $0.02024 |
| Opus 5 | $0.00036 | $0.01012 |
| Sonnet 5 | $0.00014 | $0.00405 |
| Haiku 4.5 | $0.00007 | $0.00202 |
Grade A, and why
jsonl-core 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 8d 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 — 181 lines — stays where its author put it; the contents beside it link to each section on GitHub.
JSONL Core — Conversation Parsing Infrastructure
Architecture
All parsing logic lives in ${CLAUDE_PLUGIN_ROOT}/scripts/echolib.py — a single Python module (stdlib only, Python 3.6+). The shell scripts are thin wrappers around it.
Data Locations
- Session index (fast path):
~/.claude/projects/<encoded-path>/sessions-index.json - Fallback index (built by echo-sleuth):
~/.claude/projects/<encoded-path>/.echo-sleuth-index.json - Full conversations:
~/.claude/projects/<encoded-path>/<uuid>.jsonl - Subagent conversations:
~/.claude/projects/<encoded-path>/<uuid>/subagents/agent-<id>.jsonl - Global prompt history:
~/.claude/history.jsonl
The <encoded-path> is the project's absolute path with / replaced by - (e.g., -Users-joker-github-myproject).
Important: Only ~10% of projects have sessions-index.json. The scripts automatically build a fallback index from raw .jsonl files for the remaining 90%, cached in .echo-sleuth-index.json.
Strategy: Fast Path First
Always start with the index before opening any .jsonl file:
bash ${CLAUDE_PLUGIN_ROOT}/scripts/list-sessions.sh "current" --limit 20
bash ${CLAUDE_PLUGIN_ROOT}/scripts/list-sessions.sh "all" --grep "search term" --limit 10
bash ${CLAUDE_PLUGIN_ROOT}/scripts/list-sessions.sh "/path/to/project"
Output is tab-separated: SESSION_ID CREATED MODIFIED MSG_COUNT BRANCH SUMMARY FIRST_PROMPT PROJECT_PATH FULL_PATH
The FULL_PATH field (9th column) is the absolute path to the .jsonl file. Use this to pass to other scripts.
Only open the full .jsonl when you need message-level detail.
Canonical Parser
bash ${CLAUDE_PLUGIN_ROOT}/scripts/parse-jsonl.sh <file.jsonl> [options]
Key modes:
- Schema detection (check if format has changed):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/parse-jsonl.sh <file.jsonl> --detect-schema - Filtered extraction (skip noise, ~38% faster on large files):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/parse-jsonl.sh <file.jsonl> --types user,assistant --skip-noise --limit 20 - Field selection (only extract specific fields):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/parse-jsonl.sh <file.jsonl> --types user --fields timestamp,message --format tsv
What ships with it
2 files 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.
- 8d ago First seen · 181 lines · 71 tokens per session scan A e7387293c342
jsonl-core is a skill published in the GitHub repository xiaolai/echo-sleuth-for-claude (9 stars, last pushed 15d ago), licensed ISC. It adds 71 tokens to every session and 2,024 once invoked, about $0.0004 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 2026-08-31.
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