Borrowing it
Nothing to install: this file belongs to cardstack/boxel. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/cardstack/boxel/main/.claude/skills/user-keys/SKILL.mdgit clone --depth 1 https://github.com/cardstack/boxelWrote 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/cardstack/boxel/user-keys)<a href="https://agentmods.dev/skills/cardstack/boxel/user-keys"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/user-keys/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/cardstack/boxel/user-keys"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/user-keys.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00244 | $0.02030 |
| Opus 5.5 | $0.00098 | $0.00812 |
| Sonnet 5.5 | $0.00049 | $0.00406 |
| Haiku 4.5 | $0.00024 | $0.00203 |
Grade A, and why
user-keys 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 5d 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 — 129 lines — stays where its author put it; the contents beside it link to each section on GitHub.
User keys (operators)
A key is a credential stored for one user, its owner: the Matrix user id
of the session that added it. Only the owner lists, shows, replaces or
deletes it. A key is only its secret: it records no destination, and nothing
here says where a key may be sent. The code is packages/realm-server/lib/user-keys.ts (storage,
tickets, sealing) and packages/realm-server/handlers/handle-user-keys.ts
(the routes).
No value is ever readable. No route returns one, nothing logs one, the
request log and telemetry keep only the method and path of these routes, the
read-only database role can't select the tables, and the stored value is
ciphertext under the secrets-at-rest data key (see the secrets-at-rest
skill). There is no operator path to a key's value, by design; a user who
has lost track of a value replaces it.
The tables
user_keys — one row per key:
| Column | Holds |
|---|---|
id |
UUID, minted by the realm server before sealing (the value is bound to it) |
owner |
The owner's Matrix user id |
name |
A label for people, unique among the owner's keys (user_keys_owner_name_key); two owners may share a name |
kind |
static |
state |
active |
value_ciphertext, value_nonce, value_tag, value_key_id |
The sealed value |
created_at, updated_at |
timestamptz |
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.
- 5d ago First seen · 129 lines · 244 tokens per session scan A ce7ab920b62a
user-keys is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 244 tokens to every session and 2,030 once invoked, about $0.0010 per session on Opus 5.5. 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 2026-10-21.
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