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/mb-mal/claudecode-dev-skills/spec-driven-developmentnpx skills add mb-mal/claudecode-dev-skills --skill spec-driven-developmentgit clone --depth 1 https://github.com/mb-mal/claudecode-dev-skillsWhat 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 | $0.00053 | $0.01037 |
| Opus 5 | $0.00026 | $0.00518 |
| Sonnet 5 | $0.00011 | $0.00207 |
| Haiku 4.5 | $0.00005 | $0.00104 |
Grade A, and why
spec-driven-development scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 168 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Spec-Driven Development
Use specifications as the source of truth for implementation.
Workflow
- Review specification: Parse provided spec (OpenAPI, JSON Schema, requirements doc)
- Clarify ambiguities: Ask about unclear edge cases or missing details
- Validate spec completeness: Check for inputs, outputs, errors, constraints
- Implement to spec: Generate code that matches the specification exactly
- Verify against spec: Ensure all requirements are covered
Specification formats
OpenAPI/Swagger (for APIs)
paths:
/api/orders:
post:
summary: Create new order
requestBody:
required: true
content:
application/json:
schema:
type: object
required: [customer_id, items]
properties:
customer_id:
type: integer
items:
type: array
minItems: 1
items:
type: object
properties:
product_id: { type: integer }
quantity: { type: integer, minimum: 1 }
responses:
'201':
description: Order created
'400':
description: Invalid request
JSON Schema (for data structures)
{
"$schema": "http://json-schema.org/draft-07/schema#",
"type": "object",
"required": ["name", "email"],
"properties": {
"name": { "type": "string", "minLength": 1 },
"email": { "type": "string", "format": "email" },
"age": { "type": "integer", "minimum": 0 }
}
}
Structured requirements (for features)
Feature: Order creation
Input:
- customer_id: integer, required
- items: array of {product_id, quantity}, min 1 item
Behavior:
- Verify all products exist in catalog
- Check stock availability for each item
- If any item unavailable → return 400 with list of unavailable items
- Create order in 'draft' status
- Reserve inventory
Output (201):
- order_id: string (UUID)
- total_amount: decimal
- created_at: ISO 8601 timestamp
Errors:
- 400: Invalid input or unavailable items
- 404: Customer not found
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.
- 3d ago First seen · 168 lines · 53 tokens per session scan A 9b95201ee734
spec-driven-development is a skill published in the GitHub repository mb-mal/claudecode-dev-skills (5 stars, last pushed 7mo ago), licensed Apache-2.0. It adds 53 tokens to every session and 1,037 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 2026-08-31.
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