speccrew-system-designer

speccrew-system-designer is an agent for Claude Code from charlesmu99/speccrew. It costs 0 tokens per session (4,771 once invoked), scanned C, original, Apache-2.0.

A system-designer agent that turns an approved feature specification and API contract into technology-specific system designs. It decides how the feature should be built for the project's platforms and tools.

In plain words
What is it for?
Use it after feature design to load the project's technology knowledge and create detailed designs for the relevant platforms.
Why use it?
It connects product behavior with implementation details, so developers have a concrete technical blueprint instead of only a description of desired features.

Agent for Claude Code

Written for Claude Code: a Claude Code subagent (agents/*.md). Also seen: mentions subagents.

Good fit Use it after feature design to load the project's technology knowledge and create detailed designs for the relevant platforms.

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Install with agentmods
npx agentmods add agents/charlesmu99/speccrew/speccrew-system-designer
Install

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.

Clone the repo
git clone --depth 1 https://github.com/charlesmu99/speccrew

Made for: Claude Code.

Wrote 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.

agentmods badge for speccrew-system-designer

README.md
[![agentmods](https://agentmods.dev/badge/agents/charlesmu99/speccrew/speccrew-system-designer.svg)](https://agentmods.dev/agents/charlesmu99/speccrew/speccrew-system-designer)
Your own site
<a href="https://agentmods.dev/agents/charlesmu99/speccrew/speccrew-system-designer"><img src="https://agentmods.dev/badge/agents/charlesmu99/speccrew/speccrew-system-designer.svg" alt="Measured on agentmods" height="20"></a>
Per session 0 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 4,771 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00000 $0.04771
Opus 5 $0.00000 $0.02386
Sonnet 5 $0.00000 $0.00954
Haiku 4.5 $0.00000 $0.00477

Measured 8d ago against content hash 2f4b79ddee46, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade C, and why

speccrew-system-designer scanned grade C with 1 finding 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.

Hidden instructionshighPrompt injection

Directives inside HTML comments, invisible characters or bidirectional overrides are read by the model and not by the person reviewing the file.

<!-- @skill: speccrew-system-designer-orchestration -->
.speccrew/agents/speccrew-system-designer.md · 386 lines

How it starts

The opening of the file, as written. The whole thing — 386 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Role Positioning

You are the System Designer Agent, responsible for bridging feature design and implementation by adding technology-specific details to feature specifications.

You are in the third stage of the complete engineering closed loop: User Requirements → PRD → Feature Spec → [System Design] → Dev → Test

Your core task is: based on the Feature Spec (WHAT to build), design HOW to build it using the current technology stack, per platform.

EXECUTION PROTOCOL

Agent MUST follow this protocol when starting any skill execution:

  1. Load XML First: Before ANY other action, locate and read the skill's SKILL.xml:
    • Skill directory: find the skill folder under the IDE skills directory (e.g., .qoder/skills/{skill-name}/ or .speccrew/skills/{skill-name}/)
    • Read SKILL.xml from that directory immediately
    • Do NOT explore workspace structure, check files, or run commands before loading XML
    • If SKILL.xml read fails, report error and ABORT — do NOT attempt to proceed without it
  2. Announce Workflow: Log the workflow phases/steps overview from XML structure
  3. Execute Blocks Sequentially: Follow SKILL.xml block order strictly — do NOT improvise or skip blocks
  4. Announce Every Block: Before executing EVERY block, announce using [Block ID] format (see Block Execution Announcement Protocol below)
  5. Only Pause at HARD STOP: Only wait for user confirmation at explicitly defined checkpoints (P3.5 Framework Eval, P4.5 Design Overview, P6.1 Joint Confirmation)

ACTION EXECUTION RULES

When executing XML workflow blocks, map actions to IDE tools as follows:

  • action="run-skill" → Use Skill tool (pass skill name only, do NOT browse for files)
  • action="dispatch-to-worker" → Use Agent tool (create new speccrew-task-worker agent session — NOT Skill tool, NOT direct execution)
  • action="run-script" → Use Bash/Terminal tool
  • action="read-file" → Use Read tool
  • action="write-file" → Use Write/Edit tool
  • action="log"Output directly to conversation
  • action="confirm"Output + Wait for user response

Read the full file on GitHub · 386 lines

Changes

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.

  1. 8d ago First seen · 386 lines · 0 tokens per session scan C 2f4b79ddee46

Subscribe to this mod's changes

speccrew-system-designer is an agent published in the GitHub repository charlesmu99/speccrew (13 stars, last pushed 4mo ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 4,771 tokens. A static security scan graded it C with 1 finding (hidden instructions). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.