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/fattain-naime/engineering-docs/technical-blueprintnpx skills add fattain-naime/engineering-docs --skill technical-blueprintgit clone --depth 1 https://github.com/fattain-naime/engineering-docsWhat 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 | $0.00077 | $0.03177 |
| Opus 5 | $0.00039 | $0.01588 |
| Sonnet 5 | $0.00015 | $0.00635 |
| Haiku 4.5 | $0.00008 | $0.00318 |
Grade A, and why
technical-blueprint 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 2d 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 — 247 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Purpose
Produce a Technical Design Document (TDD) that captures the engineering design of a specific feature or component with enough detail that any qualified engineer on the team can implement it correctly. This document is a thinking tool first, an artifact second - the process of writing it surfaces gaps before they become production bugs.
Unlike an architecture document (what the system is), a blueprint specifies how a specific piece will be built.
Input
Works best with: The name of the feature, component, or change to be designed. Also valuable: The technical specification or requirements document, existing codebase context, known constraints (performance targets, security requirements, API contracts that must be maintained).
Example invocation: Write a technical design document for adding TOTP-based two-factor authentication to the admin login flow. We use PHP 8.3, PDO/MySQL, and Twig templates. The TOTP secret must be stored encrypted. Recovery codes must be supported.
Key Concepts
Design Doc Philosophy (Google/Stripe Standard)
A design doc is:
- Short as possible, long as necessary. If it takes more than 45 minutes to read, it is too long.
- Trade-off focused. The Alternatives Considered section is mandatory. It proves you evaluated options.
- A conversation starter. Share early and revise often. A design doc is not a contract.
- Living. Update it as the implementation evolves. Stale design docs are worse than no design docs.
The Mandatory Sections
These three sections separate a senior engineer's design doc from a junior one:
- Alternatives Considered - What else was evaluated and why it was rejected
- Security Considerations / Threat Model - What can be attacked or abused
- Rollback Plan - What happens if this change needs to be reverted
Observability
Every new feature must be observable in production. Document in the blueprint:
- Logging: What structured log events does this feature emit? Include correlation IDs, operation type, duration, and outcome. Define log levels (ERROR for failures, WARN for degraded state, INFO for business events).
- Metrics: What metrics does this feature expose? (e.g., request count, error rate, latency histogram, queue depth, custom business metrics like "payments_processed_total").
- Tracing: How does this feature participate in distributed tracing? What spans are created? What context is propagated?
- Alerting: What conditions should trigger alerts? Define thresholds, severity levels (P1-P4), and escalation paths.
What ships with it
1 file 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.
- 2d ago First seen · 247 lines · 77 tokens per session scan A 2be6ec6bbb3d
technical-blueprint is a skill published in the GitHub repository fattain-naime/engineering-docs (4 stars, last pushed 18d ago), licensed MIT. It adds 77 tokens to every session and 3,177 once invoked, about $0.0004 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 2026-08-31.
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