What is error-handling?

A reference for how Kavo represents failures in code and in HTTP responses. It covers its exception types, error codes, and RFC 9457 problem-details format, a standard JSON shape for API errors.

Use it when mapping Kavo errors, choosing exceptions in custom handlers, or checking the failure response returned by a route.

It prevents handlers from throwing inconsistent exceptions or returning error responses that do not match the documented format.

error-handling — Skill for Claude Code by kavo-labs/kavo

Install

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.

Any agent

npx skills add kavo-labs/kavo --skill error-handling

Clone the repo

git clone --depth 1 https://github.com/kavo-labs/kavo

Made for: Claude Code.

Or install kavo-skills, the plugin that ships this one along with the rest of its 15 skills.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/kavo-labs/kavo/error-handling/github.svg)](https://agentmods.dev/skills/kavo-labs/kavo/error-handling)

Your own site

<a href="https://agentmods.dev/skills/kavo-labs/kavo/error-handling"><img src="https://agentmods.dev/badge/skills/kavo-labs/kavo/error-handling/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/kavo-labs/kavo/error-handling"><img src="https://agentmods.dev/badge/skills/kavo-labs/kavo/error-handling.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 72 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,603 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector warn 7 Sept 2026

SkillSpector: 2 findings, up to medium

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 →

medium Prompt Injection · line 42
Large whitespace padding was detected (a block of blank lines or a long run of spaces). This can push injected instructions below or to the right of the visible area so a human reviewer never sees them while the agent still reads them. Manual review of the hidden content is recommended.

Fix: Remove the large whitespace padding (blank-line blocks or long space runs) and review any content hidden below or to the right of it. Keep skill files compact and reviewable so no instructions can be
medium Excessive Agency · line 60
Skill allows unbounded resource consumption (API calls, storage, compute). Without rate limits or quotas, a compromised or misbehaving agent can cause denial-of-service or cost overruns.

Fix: Set explicit rate limits, timeouts, and resource quotas for API calls, file operations, and compute. Implement circuit breakers for runaway loops.

How audits are shown

Origin original No closer match found in the catalogue.

Token cost

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	$0.00072	$0.01603
Opus 5.5	$0.00029	$0.00641
Sonnet 5.5	$0.00014	$0.00321
Haiku 4.5	$0.00007	$0.00160

Measured 1mo ago against content hash a1eb82ad3a58, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

error-handling 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.

extensions/skills/error-handling/SKILL.md · 111 lines

How it starts

The opening of the file, as written. The whole thing — 111 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Error handling reference

One exception hierarchy (core/src/errors/), one stable code catalog, one wire shape (RFC 9457 problem details, ADR-0009). Full detail: docs/internals/architecture/06-error-handling.md.

Hierarchy

KavoException (abstract; implements the KavoExceptionShape contract)
├─ QueryValidationException     carries issues[] → errors[] extension
├─ NotFoundException
├─ ConflictException
├─ AlreadyDeletedException      soft-deleting an already-deleted row → 409
├─ NotDeletedException          restoring/purging a live row → 409
├─ OperationDisabledException
├─ OperationNotRegisteredException   registry miss, never "disabled"
├─ BulkOperationException       carries items[] (reserved — bulk not built)
├─ PersistenceException
├─ TransactionException         carries retryable: boolean
├─ ConfigurationException       bootstrap-only, never a wire response
└─ PaginationNotAdvancingException   cursor page produced its own token → 500
                                     (ADR-0021 §5); data-/adapter-dependent

Every leaf binds exactly one catalog code; status, title, and message template all come from the catalog, so a thrown exception can never disagree with its own documented response. @kavo/nest's KavoExceptionFilter (@Catch(KavoException)) is the only place Kavo touches HTTP — Kavo exceptions never extend Nest's, and core never depends on framework exception types.

Error-code catalog (`ERROR_CATALOG`, `core/src/errors/error-catalog.ts`)

Codes are API surface — renaming one is a breaking (semver) change.

Code	HTTP	Fires when	Payload extensions
`KAVO_QUERY_INVALID`	400	Any query grammar/allowlist/limit violation (aggregate)	`errors[]` of the sub-codes below
`KAVO_QUERY_INVALID_FIELD`	400	Field not on the filter/sort/select allowlist	issue-level
`KAVO_QUERY_INVALID_OPERATOR`	400	Unknown or misspelled wire operator	issue-level
`KAVO_QUERY_INVALID_VALUE`	400	Coercion failure, malformed bounds, bad pagination value	issue-level
`KAVO_QUERY_LIMIT_EXCEEDED`	400	`limits.filterDepth` / `limits.inValues` exceeded	issue-level
`KAVO_QUERY_UNSUPPORTED_PARAM`	400	`withDeleted`/`onlyDeleted` on a hard-delete entity, or from a client without `delete.allowDeletedReads`; `include` with no include resolver wired	issue-level
`KAVO_NOT_FOUND`	404	Target row missing on `findOne`/`updateOne`/`patchOne`/`deleteOne`	—
`KAVO_CONFLICT`	409	Unique/FK violation mapped by the adapter	—
`KAVO_ALREADY_DELETED`	409	Soft-deleting an already-deleted row	—
`KAVO_NOT_DELETED`	409	Restoring or purging a row that is not deleted	—
`KAVO_OPERATION_DISABLED`	405	Programmatic/HTTP call to a disabled registry entry	—
`KAVO_OPERATION_NOT_REGISTERED`	405	Programmatic call naming an operation the registry has no entry for at all	—
`KAVO_BULK_FAILED`	422	Atomic bulk failure (reserved — bulk is not built)	`items[]` per-index issues
`KAVO_PERSISTENCE_FAILED`	500	Unrecognized adapter/driver error	`cause` kept internally
`KAVO_TRANSACTION_FAILED`	500	Deadlock/serialization failure	`retryable` flag
`KAVO_CONFIG_INVALID`	500	Bootstrap config error — fails startup, never a response	—
`KAVO_PAGINATION_NOT_ADVANCING`	500	Cursor page produced the token it was given; following `meta.nextCursor` would loop forever (ADR-0021 §5)	—

Read the full file on GitHub · 111 lines

Changes

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 a1eb82ad3a58
2mo ago Changed · +3 lines ea243b396b60
2mo ago Changed 9854887bfe6d
2mo ago First seen · 108 lines · 72 tokens per session scan A 71e743f706a7

Subscribe to this mod's changes

error-handling is a skill published in the GitHub repository kavo-labs/kavo (17 stars, last pushed today), licensed MIT. It adds 72 tokens to every session and 1,603 once invoked, about $0.0003 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.

Backend and APIs TypeScript crud mikroorm mongoose nodejs rest

error-handling next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
error-handlingkavo-labs/kavo	Skill	17	today	MIT	A	72	Claude Code
nestjs-expertpersonamanagmentlayer/pcl	Skill	45	18d ago	Apache-2.0	A	81	Claude Code
prisma-8prisma/orm	Skill	48k	today	Apache-2.0	A	220	Claude Code, Codex
nestjsericrisco/rsc-harness	Skill	598	today	MIT	A	81	Claude Code, Codex
webiny-api-cms-content-modelswebiny/webiny-js	Skill	8.1k	today	none	A	313	Claude Code, Codex
webiny-api-architectwebiny/webiny-js	Skill	8.1k	today	none	A	93	Claude Code, Codex
rpcfinom/vovk	Skill	57	today	MIT	A	347	Claude Code