CtrlK
BlogDocsLog inGet started
Tessl Logo

n8n-expression-syntax

Validate n8n expression syntax and fix common errors. Use when writing n8n expressions, using {{}} syntax, accessing $json/$node variables, troubleshooting expression errors, mapping data between nodes, or referencing webhook data in workflows. Use this skill whenever configuring node fields that reference data from previous nodes — expressions are how n8n passes data between nodes, and getting the syntax wrong is the most common source of workflow errors. Also use when asked whether a complex expression hurts performance.

66

Quality

80%

Does it follow best practices?

Run evals on this skill

Adds up to 20 points to the overall score

View guide

SecuritybySnyk

Passed

No findings from the security scan

The canonical home for this skill is n8n-expression-syntax in czlonkowski/n8n-skills

SKILL.md
Quality
Evals
Security

Quality

Content

70%Weight 40%Scale 1-5

Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.

Highly actionable, executable content with a strong transform-decision workflow, but it is over-long with significant repetition across sections and references two bundle files that are absent, undermining the progressive-disclosure structure.

Suggestions

Create the referenced COMMON_MISTAKES.md and EXAMPLES.md (or remove the links), so the 'one level deep' navigation resolves to real files.

Deduplicate: consolidate the repeated webhook-.body and Code-node guidance into single canonical sections and have other sections link to them instead of restating.

Tighten the Summary/Best Practices/'When NOT to Use' sections, which restate rules already covered, to reduce token cost without losing the quick-reference value.

DimensionReasoningScore

Conciseness

Mostly efficient but padded: the same webhook-.body mistake and Code-node guidance are restated across 'CRITICAL: Webhook Data Structure', 'When NOT to Use Expressions', 'Common Mistakes', 'Best Practices', and 'Summary', and the same field-with-bracket-notation examples recur several times.

3 / 5

Actionability

Fully executable copy-paste expressions throughout — correct {{}} syntax, $json/$node/$now/$env usage, bracket notation, ternaries, Luxon date math, and an IIFE gatekeeper pattern — covering the common cases with concrete working examples.

5 / 5

Workflow Clarity

The 'transform gatekeeper' is a clearly sequenced decision order (Expression → IIFE → Code node) with explicit rationale, and debugging gives an error→cause→fix pattern, but the validation/error-recovery feedback loops are advisory lists rather than enforceable checkpoints, leaving minor gaps.

4 / 5

Progressive Disclosure

Structure is well sectioned and references COMMON_MISTAKES.md and EXAMPLES.md, but those referenced files do not exist in the bundle, so the navigation signals point at missing material and the inline content carries what should live in those separate files.

3 / 5

Total

15

/

20

Passed

Description

91%Weight 40%Scale 1-5

Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.

A strong, specific description with clear 'what' and multiple explicit 'when' triggers tied to natural user language. The only minor weakness is a touch of redundancy and scenario framing rather than a clean action list, but it does not rise to a penalty.

DimensionReasoningScore

Specificity

Names the domain (n8n expressions) and several concrete actions — 'Validate n8n expression syntax and fix common errors', 'accessing $json/$node variables', 'mapping data between nodes', 'referencing webhook data' — but some are framed as scenarios rather than distinct capabilities, leaving minor coverage gaps.

4 / 5

Completeness

Explicitly answers both what ('Validate n8n expression syntax and fix common errors') and when ('Use when writing n8n expressions...', 'Use this skill whenever configuring node fields that reference data from previous nodes', 'Also use when asked whether a complex expression hurts performance') with concrete trigger phrases.

5 / 5

Trigger Term Quality

Comprehensive natural trigger phrases including 'writing n8n expressions', 'using {{}} syntax', 'troubleshooting expression errors', 'mapping data between nodes', 'referencing webhook data', plus the literal variable names users would mention.

5 / 5

Distinctiveness Conflict Risk

Narrow n8n-expression niche with distinctive triggers ({{}} syntax, $json/$node variables, webhook data, node field configuration); minimal overlap risk with adjacent n8n skills since the scope is explicitly scoped to expression syntax.

5 / 5

Total

19

/

20

Passed

Validation

87%

Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.

Validation14 / 16 Passed

Validation for skill structure

CriteriaDescriptionResult

skill_md_line_count

SKILL.md is long (600 lines); consider splitting into references/ and linking

Warning

relative_links

Relative link issues: 4 missing

Warning

Total

14

/

16

Passed

Repository
czlonkowski/n8n-mcp
Reviewed

Table of Contents

Is this your skill?

If you maintain this skill, you can claim it as your own. Once claimed, you can manage eval scenarios, bundle related skills, attach documentation or rules, and ensure cross-agent compatibility.