---
id: R11
family: GR-VAL
level: core
profiles: [storage-api]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-val/r11
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# R11 — A configured expression must be valid for its engine at save

*GR-VAL (Part I) · level: core · profiles: storage-api · added in 1.0*

An expression that cannot parse can only fail once the workflow is already running. Catching it at save turns a runtime failure into an editing error.

## The rule

> **Normative.** This is the rule.
>
> 1. Every expression carried in a node's configuration must pass its engine's validation when the workflow is saved.
>
> 2. A failure is refused with `R11_EXPRESSION_INVALID`, and the error names the node, the config key, the engine and the expression.
>
> 3. The expressions checked are the ones the node types declare as expression-bearing: a data extractor's `path`, the `value` of each dynamic output of a data mapper, the sources of a data shaper's `mapping` (with reserved source values such as a literal or a now marker skipped, and nested `_source` and `_each` sources walked), and a prompt template's `template`.
>
> 4. An empty expression is always valid.
>
> 5. An expression naming an engine the implementation does not know is not reported here; R6's `enum` check on the engine key owns that error.
>
> 6. An engine whose validation raises rather than returning a verdict is treated as a rejection, yielding one `R11_EXPRESSION_INVALID` for that expression; the failure is never propagated, so a misbehaving engine still produces a refusal against the workflow and never a server error.

## Why

Recorded under OPEN-3.

## Related rules

- Names: R6.d
- Referenced by: R6.k

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.