Name: falco
Rating: 71.2 (1 reviews)
Author: fastly

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.

Quality

86%

Does it follow best practices?

Impact

—

No eval scenarios have been run

Securityby

Advisory

Suggest reviewing before use

Quality

Content

72%

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

This is a well-structured skill with strong actionability and excellent progressive disclosure. Its main weaknesses are moderate redundancy between the two source-code-as-reference sections and the lack of an explicit multi-step workflow with validation checkpoints for the common lint-fix-deploy cycle. The common VCL issues section is a valuable addition that demonstrates domain expertise.

Suggestions

Add an explicit multi-step workflow (e.g., 'lint → fix errors → re-lint → test → simulate → deploy') with validation checkpoints and a feedback loop for error recovery.

Consolidate the two 'source code as reference' sections (the prose section and the quick lookup table) into a single concise section to reduce redundancy.

Remove or shorten the trigger/scope section since this information is already captured in the YAML frontmatter description.

Dimension	Reasoning	Score
Conciseness	Generally efficient but has some redundancy — the 'Source Code as VCL Reference' quick lookup table largely duplicates the earlier 'Using Falco Source as VCL Reference' section, and the trigger/scope section restates what the YAML description already covers. Some explanatory prose (e.g., 'Equally important, the falco source code is the most complete machine-readable specification') could be trimmed.	2 / 3
Actionability	Provides fully executable commands for every workflow (lint, test, simulate, format, terraform), concrete configuration YAML, specific common VCL issues with exact fixes (e.g., '86400s' not '86400'), and precise source file paths for lookups. All examples are copy-paste ready.	3 / 3
Workflow Clarity	Individual commands are clear, but there's no explicit multi-step workflow with validation checkpoints — e.g., no 'lint → fix → re-lint → test → simulate' pipeline with feedback loops. The 'Common VCL Issues' section helps but is presented as a reference list rather than integrated into a validation workflow. For a tool that catches errors before deployment, a lint-fix-verify loop should be explicit.	2 / 3
Progressive Disclosure	Excellent structure with a clear overview in the main file and a well-organized references table pointing to 8 topic-specific files, each with a 'Use when...' column. References are one level deep and clearly signaled. The source code lookup table provides a second navigation path for VCL reference questions.	3 / 3
	Total	10 / 12 Passed

Description

100%

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

This is an excellent skill description that thoroughly covers specific capabilities, provides extensive natural trigger terms, explicitly states both what the skill does and when to use it, and occupies a highly distinct niche. The description is comprehensive without being padded with fluff, and uses proper third-person voice throughout.

Dimension	Reasoning	Score
Specificity	Lists multiple specific concrete actions: lints, tests, simulates, formats VCL code, serves as VCL reference, validates syntax, runs linting, tests locally, simulates request handling, formats files, writes unit tests with assertions, debugs logic errors, looks up function signatures/variable scopes.	3 / 3
Completeness	Clearly answers both 'what' (lints, tests, simulates, formats VCL code, serves as VCL reference) and 'when' with an explicit 'Use when...' clause listing numerous specific trigger scenarios including validating syntax, running linting, testing locally, debugging logic errors, looking up function signatures, and more.	3 / 3
Trigger Term Quality	Excellent coverage of natural terms users would say: 'VCL', 'falco', 'lint', 'simulate', 'test', 'fmt', 'VCL syntax errors', 'type mismatches', 'VCL subroutine', 'falco lint', 'falco simulate', 'falco test', 'falco fmt', 'Fastly VCL', 'VCL unit tests', 'VCL function signatures', 'variable scopes'. These are highly specific and match what a user working with Fastly VCL would naturally say.	3 / 3
Distinctiveness Conflict Risk	Extremely distinct niche: Fastly VCL code using the falco tool. The combination of 'VCL', 'Fastly', and 'falco' creates a very specific domain that is unlikely to conflict with any other skill. The specific CLI commands (falco lint/simulate/test/fmt) further reduce conflict risk.	3 / 3
	Total	12 / 12 Passed

Validation

100%

Warnings & errors only

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

Validation — 11 / 11 Passed

Validation for skill structure

No warnings or errors.

Repository: fastly/fastly-agent-toolkit
Commit: 73af5b9

Reviewed: 13 days ago

Table of Contents

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