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 skills add existential-birds/beagle --skill go-web-expertgit clone --depth 1 https://github.com/existential-birds/beagleWrote 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/existential-birds/beagle/go-web-expert)<a href="https://agentmods.dev/skills/existential-birds/beagle/go-web-expert"><img src="https://agentmods.dev/badge/skills/existential-birds/beagle/go-web-expert/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/existential-birds/beagle/go-web-expert"><img src="https://agentmods.dev/badge/skills/existential-birds/beagle/go-web-expert.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00045 | $0.03704 |
| Opus 5.5 | $0.00018 | $0.01482 |
| Sonnet 5.5 | $0.00009 | $0.00741 |
| Haiku 4.5 | $0.00005 | $0.00370 |
Grade A, and why
go-web-expert scanned grade A with 0 findings 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 1mo 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 451 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Go Web Expert System
Five non-negotiable rules for production-quality Go web applications. Every handler, every service, every line of code must satisfy all five.
Quick Reference
| Topic | Reference |
|---|---|
| Validation tags, custom validators, nested structs, error formatting | references/validation.md |
| httptest patterns, middleware testing, integration tests, fixtures | references/testing-handlers.md |
Rules of Engagement
| # | Rule | One-Liner |
|---|---|---|
| 1 | Zero Global State | All handlers are methods on a struct; no package-level var for mutable state |
| 2 | Explicit Error Handling | Every error is checked, wrapped with fmt.Errorf("doing X: %w", err) |
| 3 | Validation First | All incoming JSON validated with go-playground/validator at the boundary |
| 4 | Testability | Every handler has a _test.go using httptest with table-driven tests |
| 5 | Documentation | Every exported symbol has a Go doc comment starting with its name |
Hard gates (new HTTP handler)
Apply in order. Do not treat the next step as done until the Pass when for the current step is satisfied (objective evidence on disk or in test output—not “I checked mentally”).
-
Dependencies (Rule 1) — Pass when: the handler is a method on a struct that holds every mutable dependency (
db, logger, HTTP clients, caches); any new package-levelvaris only in the allowlist under What Is Allowed at Package Level. Evidence: constructor wires deps; no new forbidden globals from that list. -
Boundary (Rule 3) — Pass before calling service/domain code: Pass when: the request decodes into a tagged struct and
validate.Struct(or equivalent) runs; invalid JSON and validation failures have defined HTTP status bodies (e.g. 400/422). Evidence: decode +validate.Structappear in the handler; tests or manual run show 422/400 for bad input.
What ships with it
2 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.
- 1mo ago First seen · 451 lines · 45 tokens per session scan A 606424da65ce
go-web-expert is a skill published in the GitHub repository existential-birds/beagle (82 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 45 tokens to every session and 3,704 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-16.
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