Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/fastly/fastly-agent-toolkit/falconpx skills add fastly/fastly-agent-toolkit --skill falcogit clone --depth 1 https://github.com/fastly/fastly-agent-toolkitWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/fastly/fastly-agent-toolkit/falco)<a href="https://agentmods.dev/skills/fastly/fastly-agent-toolkit/falco"><img src="https://agentmods.dev/badge/skills/fastly/fastly-agent-toolkit/falco.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00173 | $0.02316 |
| Opus 5 | $0.00086 | $0.01158 |
| Sonnet 5 | $0.00035 | $0.00463 |
| Haiku 4.5 | $0.00017 | $0.00232 |
Grade A, and why
falco scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
# Default port is 3124. Test with: curl http://localhost:3124/path How it starts
The opening of the file, as written. The whole thing — 181 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Trigger and scope
Trigger on: VCL files, .vcl extensions, XVCL files, .xvcl extensions, falco CLI, VCL unit tests, VCL linting/simulation/formatting, VCL REPL, beresp/bereq/req.http variables, subroutine scopes, backend/ACL/director/table declarations, edge dictionaries, validating VCL in Terraform plans, or running/testing XVCL scripts locally.
Do NOT use for: generic non-Fastly VCL, Fastly Compute/WASM, Fastly API/dashboard ops, CDN comparison, cache purging, or authoring Terraform resources.
Falco — VCL Development Tool & Reference
Falco is a Fastly VCL development tool for linting, testing, simulating, and formatting VCL code. Equally important, the falco source code is the most complete machine-readable specification of Fastly's VCL dialect — its parser, interpreter, and type system document every variable, function, type, and scope rule in VCL.
Official VCL documentation: https://www.fastly.com/documentation/guides/full-site-delivery/fastly-vcl/about-fastly-vcl/
Falco documentation: https://github.com/ysugimoto/falco
Using Falco Source as VCL Reference
If you need to understand how VCL works — what variables exist, which scopes they're available in, what functions are built-in, how types coerce — the falco source code is your best reference. It's a complete Go implementation of Fastly's VCL 2.x and is more precise than prose documentation.
If the falco source is not available locally, recommend cloning it:
git clone https://github.com/ysugimoto/falco.git ~/src/falco
Once available locally, read the source files directly to answer VCL questions. See understanding-vcl-from-source.md for a detailed guide on which files to read for different VCL topics.
Install
# Homebrew
brew install falco
# From source (requires Go 1.25+)
go install github.com/ysugimoto/falco/cmd/falco@latest
# Or clone and build
git clone https://github.com/ysugimoto/falco.git
cd falco
make darwin_arm64 # or darwin_amd64, linux_amd64, linux_arm64
What ships with it
8 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 4d ago First seen · 181 lines · 173 tokens per session scan A 3f428cde4558
falco is a skill published in the GitHub repository fastly/fastly-agent-toolkit (32 stars, last pushed 3d ago), licensed MIT. It adds 173 tokens to every session and 2,316 once invoked, about $0.0009 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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