Borrowing it
Nothing to install: this file belongs to kavo-labs/kavo. 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/kavo-labs/kavo/main/.claude/skills/add-exception/SKILL.mdgit clone --depth 1 https://github.com/kavo-labs/kavoWrote 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/kavo-labs/kavo/add-exception)<a href="https://agentmods.dev/skills/kavo-labs/kavo/add-exception"><img src="https://agentmods.dev/badge/skills/kavo-labs/kavo/add-exception/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/kavo-labs/kavo/add-exception"><img src="https://agentmods.dev/badge/skills/kavo-labs/kavo/add-exception.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 | $0.00051 | $0.00950 |
| Opus 5.5 | $0.00020 | $0.00380 |
| Sonnet 5.5 | $0.00010 | $0.00190 |
| Haiku 4.5 | $0.00005 | $0.00095 |
Grade A, and why
add-exception 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 1mo 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 — 74 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Adding an exception
Kavo has one exception hierarchy, one error-code catalog, and one wire shape
(RFC 9457 problem details, ADR-0009) — docs/internals/architecture/06-error-handling.md.
A new failure mode is a new catalog entry, never a raw Error, a bare string
code, or a second serialization path.
Decide it's actually new
Check ERROR_CATALOG (packages/core/src/errors/error-catalog.ts) and the
hierarchy first — a new failure mode for an existing code (e.g. another
reason a request is malformed) is usually a QueryValidationException issue,
not a new class. Only add a leaf when the failure needs its own HTTP status,
its own payload shape, or callers need to instanceof/catch it distinctly.
Where it goes
- The class — a new leaf under
KavoException(packages/core/src/errors/), named*Exception. It implements theKavoExceptionShapecontract; downstream layers (including@kavo/nest's filter and@kavo/next'stoErrorResponse) program against that shape, never the concrete class, so don't add fields the base contract can't express without extending the contract itself. - The catalog entry —
ERROR_CATALOGgets one row: a stableKAVO_SNAKE_CASEcode, HTTP status, title, and an English message template with{param}placeholders. Codes are public API surface — once shipped, renaming one is a breaking change. Pick the name you're willing to keep. - Payload extensions, if any — follow the existing pattern rather than
inventing a shape: issue-level detail lives in
errors[](query validation), per-item detail initems[](bulk), a typed flag alongside the message (retryableonTransactionException). A new top-level wire field needs a reasonerrors[]/items[]can't already carry it. ErrorContext— the throw site doesn't need to fillentityName/operation/correlationIditself;DefaultErrorHandlerbackfills whatever's missing. Don't hand-roll that at the throw site.- Adapter mapping, if it originates from
@kavo/typeorm— add the translation in the adapter's own table (mapDriverError, doc 09 §5) inside the adapter package. Core never gains ORM-specific knowledge to recognize a driver error; whatever the adapter doesn't recognize already falls through toPersistenceExceptionwith the original ascause. exposeInternals— if the new exception can carry adapter/driver detail, gate it behinderrors.exposeInternals(defaultfalse) the same wayPersistenceException.causeis gated — never leak it unconditionally.
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.
- 1mo ago Changed · +1 lines 0311a0c85d7a
- 1mo ago First seen · 73 lines · 51 tokens per session scan A 68a771e20da3
add-exception is a skill published in the GitHub repository kavo-labs/kavo (17 stars, last pushed today), licensed MIT. It adds 51 tokens to every session and 950 once invoked, about $0.0002 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 2026-09-02.
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