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falco

Lints, tests, simulates, and formats Fastly VCL code using the falco tool. Also serves as the authoritative VCL reference via the falco Go source, which implements Fastly's full VCL dialect. Use when validating VCL syntax, running VCL linting, testing VCL locally, simulating VCL request handling, formatting VCL files, writing VCL unit tests with assertions, debugging VCL logic errors, looking up VCL function signatures or variable scopes, understanding VCL subroutine behavior, or running `falco lint`/`falco simulate`/`falco test`/`falco fmt`. Also applies when working with VCL syntax errors, type mismatches in VCL, choosing which VCL subroutine to use, or setting up a local VCL development and testing environment.

75

Quality

93%

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SKILL.md
Quality
Evals
Security

Quality

Content

86%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.

Well-structured, actionable reference for the falco tool with executable commands and a clean one-level-deep reference layout. Minor redundancy in the source-as-reference guidance keeps it just short of fully lean.

Suggestions

Consolidate the 'Using Falco Source as VCL Reference' section and the 'Source Code as VCL Reference (Quick Lookup)' table into a single block to remove overlap.

Add an explicit lint→fix→re-lint feedback loop (e.g., 'Run falco lint, fix reported errors, re-run until clean') to elevate workflow clarity.

Trim the duplicated clone instruction (it appears in both the main body and the reference guidance).

DimensionReasoningScore

Conciseness

Efficient and assumes Claude's competence — no basic VCL explanations — but the source-as-reference guidance is covered twice (a conceptual section and a lookup table), which could be consolidated.

4 / 5

Actionability

Fully executable, copy-paste-ready commands throughout: install commands, 'falco -vv -I ./vcl ./vcl/main.vcl', 'falco simulate -p 8080', a complete .falco.yaml example, and the terraform pipe.

5 / 5

Workflow Clarity

Quick reference sequences common workflows (lint before deploy, run tests, watch mode, simulate locally) with concrete commands, but it reads as a command catalog rather than an explicit validate-fix-retry feedback loop.

4 / 5

Progressive Disclosure

Clear overview with a References table mapping each topic to a real one-level-deep bundle file (all verified present in references/) plus a 'Use when' column, making navigation easy.

5 / 5

Total

18

/

20

Passed

Description

100%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, third-person description that clearly states capabilities and provides an exhaustive 'Use when' trigger list. It is comprehensive yet avoids vague fluff.

DimensionReasoningScore

Specificity

Lists multiple concrete actions — 'Lints, tests, simulates, and formats Fastly VCL code' — plus the reference role, giving comprehensive coverage of what the tool does.

5 / 5

Completeness

Explicitly answers both 'what' (lints/tests/simulates/formats + authoritative reference) and 'when' via a detailed 'Use when ...' clause with concrete trigger phrases.

5 / 5

Trigger Term Quality

Comprehensive natural terms including 'VCL syntax', 'linting', 'simulating VCL request handling', 'VCL unit tests', 'type mismatches', and the literal 'falco lint'/'falco simulate'/'falco test'/'falco fmt' commands users would say.

5 / 5

Distinctiveness Conflict Risk

Scoped tightly to Fastly VCL and the falco tool with highly specific triggers, making conflict with unrelated skills minimal.

5 / 5

Total

20

/

20

Passed

Validation

100%

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

Validation16 / 16 Passed

Validation for skill structure

No warnings or errors.

Repository
fastly/fastly-agent-toolkit
Reviewed

Table of Contents

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