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 oborchers/fractional-cto --skill prefixed-idsgit clone --depth 1 https://github.com/oborchers/fractional-ctoWrote 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/oborchers/fractional-cto/prefixed-ids)<a href="https://agentmods.dev/skills/oborchers/fractional-cto/prefixed-ids"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/prefixed-ids/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/oborchers/fractional-cto/prefixed-ids"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/prefixed-ids.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00069 | $0.02919 |
| Opus 5 | $0.00034 | $0.01460 |
| Sonnet 5 | $0.00014 | $0.00584 |
| Haiku 4.5 | $0.00007 | $0.00292 |
Grade A, and why
prefixed-ids 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 10d 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 — 193 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Every ID Should Declare Its Type
When a support engineer sees cus_NffrFeUfNV2Hib in a log line, they know it is a customer. When they see 550e8400-e29b-41d4-a716-446655440000, they know nothing. Stripe prefixes every ID with a short type indicator, and that seemingly small decision compounds across debugging, routing, type safety, log analysis, and cross-service communication. Adopt this pattern for every resource in your API.
The Prefix Pattern
Every ID follows the format {type}_{random}:
cus_NffrFeUfNV2Hib -- customer
ord_01HXK3GJ5V8WJKPT2MNR -- order
pi_3MtwBwLkdIwHu7ix28a3 -- payment intent
The prefix is a short, lowercase abbreviation of the resource type. The underscore is a fixed separator. The random part is a collision-resistant, alphanumeric string.
Format Rules
Follow these constraints for every prefixed ID:
- Prefix length: 2-5 lowercase characters. Short enough to read at a glance, long enough to be unambiguous.
- Separator: Always a single underscore. Never a hyphen, colon, or dot.
- Random part: Base62 characters (
a-zA-Z0-9). URL-safe, no special characters. 14-27 characters depending on the generation strategy. - Total length: 18-30 characters. Short enough to paste in Slack, long enough to be collision-free.
Prefix Catalog
Define a canonical prefix for every resource type in your API. Maintain this as a living registry -- never reuse a prefix for a different resource.
| Prefix | Resource | Example |
|---|---|---|
usr_ |
User | usr_01HXK3GJ5V8WJKP |
org_ |
Organization | org_2ZutauDiLLuKvLgb |
ord_ |
Order | ord_01ARZ3NDEKTSV4RR |
prod_ |
Product | prod_NWjs8kKbJWmuuc |
inv_ |
Invoice | inv_1MtHbELkdIwHu7ix |
pay_ |
Payment | pay_3MtwBwLkdIwHu7ix |
sub_ |
Subscription | sub_1MowQVLkdIwHu7ix |
wh_ |
Webhook Endpoint | wh_1MqVTHLkdIwHu7ix |
evt_ |
Event | evt_9Kx2mPbQ7rTvYw4j |
sess_ |
Session | sess_2dH3VUuCJRx7wnlv |
tok_ |
Token | tok_1MioVOLkdIwHu7ix |
key_ |
API Key | key_4eC39HqLyjWDarjt |
cus_ |
Customer | cus_NffrFeUfNV2Hib |
price_ |
Price | price_1MoBy5LkdIwHu7ix |
txn_ |
Transaction | txn_3MmlLrLkdIwHu7ix |
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.
- 10d ago First seen · 193 lines · 69 tokens per session scan A 070768d1243c
prefixed-ids is a skill published in the GitHub repository oborchers/fractional-cto (29 stars, last pushed 1mo ago), licensed MIT. It adds 69 tokens to every session and 2,919 once invoked, about $0.0003 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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