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 proyecto26/system-design-skills --skill dnsgit clone --depth 1 https://github.com/proyecto26/system-design-skillsWrote 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/proyecto26/system-design-skills/dns)<a href="https://agentmods.dev/skills/proyecto26/system-design-skills/dns"><img src="https://agentmods.dev/badge/skills/proyecto26/system-design-skills/dns.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 5.1 | $0.00131 | $0.02742 |
| Opus 5 | $0.00066 | $0.01371 |
| Sonnet 5 | $0.00026 | $0.00548 |
| Haiku 4.5 | $0.00013 | $0.00274 |
Grade A, and why
dns 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 8d 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 — 169 lines — stays where its author put it; the contents beside it link to each section on GitHub.
DNS
DNS is the global front door: it turns a name (api.example.com) into an address
before any request reaches your servers. It is also a routing layer — the same
lookup can hand different clients different answers (by region, latency, health,
or weight). Get it wrong and clients reach a dead region, fail over in minutes
instead of seconds, or cache a bad answer for hours. It is not a load balancer
and not a CDN; it decides which endpoint a client is told to use, not how bytes
are balanced inside that endpoint.
When to reach for this
A service is reachable by a stable hostname; traffic must be steered to the closest or healthiest region/data center; or an endpoint's IP can change (a new load balancer, a failover site) and clients must follow without code changes. Multi-region or multi-data-center designs need DNS to pick the entry point; single-region designs still need it for a stable, movable name.
When NOT to
Routing inside one region — that is a load balancer's job (→ load-balancing),
which reacts in milliseconds, not TTL-bound minutes. Fine-grained per-request or
session-aware steering — DNS answers per lookup, then the client caches it. Fast
failover with sub-second recovery — DNS failover is gated by TTL and resolver
caching; do not promise instant cutover from the name layer. And do not reach for
exotic routing policies before a number shows users are spread across regions
(YAGNI) — a single A/ALIAS record is the right default for one region.
Clarify first
- Geographic spread — one region or many? Where are the users? (→
requirements-scoping) - Failover target — recovery time objective for losing a region: seconds, or "a few minutes is fine"?
- How dynamic is the endpoint — fixed IPs, or an LB hostname that changes? (drives
AvsCNAME/ALIAS) - Steering goal — closest by latency, by user geography, by weight (canary/A-B), or just round-robin?
- Staleness tolerance for the mapping — how long can a client keep a stale answer? (sets the TTL →
back-of-the-envelope)
What ships with it
5 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.
- 8d ago First seen · 169 lines · 131 tokens per session scan A b387a3ed8d0d
dns is a skill published in the GitHub repository proyecto26/system-design-skills (69 stars, last pushed 3mo ago), licensed MIT. It adds 131 tokens to every session and 2,742 once invoked, about $0.0007 per session on Opus 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 2026-08-30.
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