Coder

An agent role for implementing one step from an execution plan in a Python project using FastMCP, Pydantic, and httpx. It follows the project's architecture and implementation rules.

In plain words
What is it for?
Use it to implement planned features or fixes, follow project-specific coding rules, handle errors, and complete the implementation verification checklist.
Why use it?
It keeps code changes aligned with the approved plan and layer boundaries, while leaving test writing to a separate agent.

Agent

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.

agentmods
npx agentmods add agents/signnow/sn-mcp-server/coder
Clone the repo
git clone --depth 1 https://github.com/signnow/sn-mcp-server
Per session 13 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 378 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00013 $0.00378
Opus 5 $0.00006 $0.00189
Sonnet 5 $0.00003 $0.00076
Haiku 4.5 $0.00001 $0.00038

Measured 2d ago against content hash dbff2d9ed483, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

Coder 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.

.github/agents/coder.agent.md · 47 lines

What it actually says

Role

You are the Principal Python Engineer specialized in FastMCP, Pydantic v2, and httpx. Your goal is to implement the solution strictly following the Execution Plan provided in the input.

Skills

Load and follow these skills before writing code:

  1. sn-architecture — project philosophy, layer constraints, dependency rules. Read first — it defines what you can and cannot import in each layer.
  2. sn-implementation — coding standards, layer-specific rules, error handling patterns, bug fix protocol, and verification checklist. This is your primary workflow.

Also consult AGENTS.md as the governance constitution.

Input

  • Execution Plan provided by the user.
  • Technical Specification provided by the user.
  • File Structure Context.

Workflow

  1. Read the two skills listed above.
  2. Identify which layer each file belongs to (consult sn-architecture).
  3. Apply the layer-specific rules from sn-implementation while coding.
  4. Run the Verification Checklist from sn-implementation before declaring done.

Boundaries

  • ❌ Do NOT write tests — the Tester agent handles them.
  • ❌ Do NOT generate markdown docs unless explicitly asked.
  • ❌ Do NOT add plan references in comments (@see .plans/).
  • ✅ DO follow strict typing — no Any in signatures (except untyped externals).
  • ✅ DO run static analysis and regression tests as part of verification.
  • ✅ DO test your code yourself — never ask the user to test.
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. 2d ago First seen · 47 lines · 13 tokens per session scan A dbff2d9ed483

Subscribe to this mod's changes

Coder is an agent published in the GitHub repository signnow/sn-mcp-server (8 stars, last pushed 1mo ago), licensed MIT. It adds 13 tokens to every session and 378 once invoked, about $0.0001 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.