# Use a built-in check > Name one of Kindgi's built-in checks in a guardrail instead of writing your own, and give it the settings it reads. This guide puts one of Kindgi's built-in checks on an agent, instead of a check you write, and lists the settings each one reads. Kindgi has seven built-in checks for common rules: words an answer must or mustn't contain, a pattern it must match, citations, and which tools a turn may call, how many and in what order. A guardrail can name one instead of shipping a check you [write yourself](https://docs.kindgi.com/v0.1.9/guides/guardrails/write-a-guardrail.md). ## Before you start - **A TypeScript pack,** with Kindgi 0.1's SDK, on a runtime such as `kindgi dev`. A Python, Java or Scala pack can't name a built-in. - **An agent to put the guardrail on.** ## Name a built-in A built-in check needs no code of yours. The guardrail names the built-in as its `check`, gives its `config`, and ships no check implementation. Ask your coding agent: "I want a guardrail, with a built-in check, that stops an answer promising a guarantee." Kindgi's skills in your pack tell it how ([How it knows Kindgi](https://docs.kindgi.com/v0.1.9/start/coding-agents.md)). For reference, the guardrail looks like this: `guardrails/no-guarantees/index.ts` ```ts export default { id: 'my-pack.no-guarantees', name: 'Never promise a guarantee', kind: 'zero-llm', check: 'forbidden-substring', config: { patterns: ['guaranteed', 'we promise'] }, action: { 'on-violation': 'halt' }, severity: 'error', }; ``` Put it on an agent by its id, as with any guardrail, as [Put it on an agent](https://docs.kindgi.com/v0.1.9/guides/guardrails/write-a-guardrail.md#put-it-on-an-agent) shows. With `halt`, an answer containing "guaranteed" stops the turn, as [A halted turn](https://docs.kindgi.com/v0.1.9/guides/guardrails/halt-or-record.md#a-halted-turn) describes. The failure gives the check's reason. For a `must-cite` guardrail on an answer without a citation: ```text Error [guardrail-violation]: Turn blocked by guardrail 'acme.cite-or-halt': expected >= 1 citations, found 0 ``` A Python, Java or Scala pack can't name a built-in: a guardrail there is always defined with its own check. Python's `@guardrail` decorates a check function. Write the rule as your own check, and use [The built-in checks](https://docs.kindgi.com/v0.1.9/guides/guardrails/use-a-built-in-check.md#the-built-in-checks) for what each built-in checks. ## The built-in checks A tool list holds tool ids, as `.`. A setting in **bold** is required. | Check | Fails when | `config` | | --------------------- | ----------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `must-cite` | the answer is empty, or has fewer than `minCitations` matches of `sourcePattern` | `minCitations`: a whole number, 1 or more (1 by default); `sourcePattern`: a regular expression (by default, citations in square brackets, such as `[ord_1003]`) | | `never-call-tool` | the turn called any tool in `tools` | **`tools`**: a list of one or more tool ids | | `max-tool-calls` | the turn made more than `max` tool calls | `max`: a whole number, 0 or more (10 by default) | | `output-matches` | the answer doesn't match `pattern`, or, with `negate: true`, it does | **`pattern`**: a regular expression; `flags`: regular-expression flags (`d`, `g`, `i`, `m`, `s`, `u`, `v`, `y`), such as `"i"`; `negate`: `true` or `false` | | `tool-order` | the tools in `sequence` weren't called in that order (other calls may come between) | **`sequence`**: a list of one or more tool ids | | `required-substring` | the answer is empty, or lacks any of `patterns` | **`patterns`**: a list of one or more plain-text strings; `caseSensitive` (`false` by default) | | `forbidden-substring` | the answer contains any of `patterns` | **`patterns`**: a list of one or more plain-text strings; `caseSensitive` (`false` by default) | A config the check doesn't take is refused: a required setting left out, a setting of the wrong type, one the check doesn't know, or a regular expression that doesn't compile, or is longer than 8,192 characters with its flags. Registering such a guardrail answers `422 guardrail-config-invalid`, with each problem in `details.issues`. Deploying a pack with one fails with `deployment-validation-failed`. If one reaches a turn anyway, its check can't run, so with `halt` the turn stops, as [When the check can't run](https://docs.kindgi.com/v0.1.9/guides/guardrails/halt-or-record.md#when-the-check-cant-run) describes. ## Your own check under a built-in's name The built-in ids are reserved. A pack that ships its own check under one, such as a `defineCheck({ id: 'must-cite', … })`, is refused when you build it, with `reserved-check-id`, or `DefinitionError` in Python. Give your check a name of its own, such as `my-pack.checks.must-cite`. Or, to use the built-in, name it and drop your implementation. A current CLI marks a guardrail that only names a built-in. A pack built with an older CLI may lack that mark. A guardrail that names a built-in, comes with its pack's code, and lacks the mark gets one warning in the runtime's log each time the runtime loads the guardrail. The built-in runs either way. If the guardrail only names the built-in, rebuild the pack with a current CLI and the warning goes. If its module is your own check, give that check a name of its own: the built-in has been running in its place. ## Next - [Write a guardrail](https://docs.kindgi.com/v0.1.9/guides/guardrails/write-a-guardrail.md) - [Configure a guardrail](https://docs.kindgi.com/v0.1.9/guides/guardrails/configure-a-guardrail.md) - [Stop a turn or record a violation](https://docs.kindgi.com/v0.1.9/guides/guardrails/halt-or-record.md)