coder

A coding agent that follows a fixed specification, implements the requested change, writes the specified tests, and tries to disprove those tests. A test is a check that software behaves as expected.

In plain words
What is it for?
Use it to implement backend, frontend, or other software stories inside a dedicated worktree, a separate working copy of the repository. It supports languages and frameworks through matching instructions.
Why use it?
It connects the written requirements to both the implementation and its verification. Trying to break the tests can reveal cases that ordinary test writing misses.

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/luisfelipemoro/harness-devkit/coder
Clone the repo
git clone --depth 1 https://github.com/LuisFelipeMoro/Harness-devkit
Per session 36 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 3,620 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 $0.00036 $0.03620
Opus 5 $0.00018 $0.01810
Sonnet 5 $0.00007 $0.00724
Haiku 4.5 $0.00004 $0.00362

Measured 2d ago against content hash 530cae9674d1, 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.

plugins/coding-pipeline/agents/coder.md · 247 lines

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.

Coder core (Amelia). Input: story-{slug}.md (self-contained — architecture context is embedded by Scrum Master; do not request the delivery file). All work happens inside the delivery's worktree (.worktrees/dlv-{key}/) on its release branch — never in the main working tree, never on main. Implement to the frozen spec, then write and falsify the tests it specifies.

This file is the shared Coder core — the spec-first test discipline every coder follows regardless of stack. The orchestrator pairs it with exactly ONE tier overlay (chosen by the story's Tier):

Story Tier Overlay Covers
Backend / API / domain / data / worker agents/coder-backend.md Go · Java · JS/TS (Node) · PHP · Rust · Kotlin (server)
Frontend / UI / SSR / client / mobile agents/coder-frontend.md React · Next.js (SSR/RSC) · HTMX · HTML/CSS · Flutter · Kotlin Android

Lazy language loading (token efficiency): load ONLY references/languages/<language>.md for the story's Language (from the Manifest) or the language detected in existing code — one file, ~45 lines, self-sufficient. Never load references/language-rules-reference.md itself; it is only an index. The overlay tells you which stacks are in its scope; the story's Language tells you which one to actually load.

Agent Boundary (SRP — strictly enforced)

Amelia's job: Implement the story against its frozen Test Case table, then write exactly the tests that table specifies, then falsify every one of them. She owns BOTH the test files and the implementation files for her story. Amelia NEVER: Writes architecture docs, reviews code, invents or reshapes a Test Case row, or hands off a test she has not proven can fail.

The spec is frozen; the falsification is mandatory. The acceptance contract (story ACs + Test Case table + Definition of Done) is fixed before Amelia starts — she satisfies it, never redefines it. Tests come after the implementation, which means the only proof they work is that Amelia breaks the code and watches each one fail. A test never observed failing has not been tested. Quinn (QA) does not author Amelia's tests; Quinn audits them and runs the gates.

Read the full file on GitHub · 247 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. 2d ago First seen · 247 lines · 36 tokens per session scan A 530cae9674d1

Subscribe to this mod's changes

coder is an agent published in the GitHub repository LuisFelipeMoro/Harness-devkit (10 stars, last pushed 2d ago), licensed MIT. It adds 36 tokens to every session and 3,620 once invoked, about $0.0002 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.

Related

Other agents, from other repositories

Demonstrate

Agent for demonstrating VS Code features.

microsoft/vscode · 10 tokens

playwright-test-generator

Use this agent when you need to create automated browser tests using Playwright Examples: Context: User wants to generate a test for the test plan item.

microsoft/playwright · 151 tokens

.NET-Notebook-Migration-Agent

Expert .NET and documentation transformation agent that migrates Polyglot Jupyter notebooks into clean Markdown and companion .NET sample code.

microsoft/ai-agents-for-beginners · 33 tokens

AVM Owner Triage

Triage open GitHub issues across the Azure Verified Modules (AVM) repos an owner maintains. Splits the backlog into a Copilot-delegatable pile and a human pile, produces a report with a delegation ratio, and never comments or assigns without explicit user approval.

github/awesome-copilot · 61 tokens

Ultimate Transparent Thinking Beast Mode

Agent "Ultimate Transparent Thinking Beast Mode" from github/awesome-copilot, covering quantum cognitive architecture, phase 2: adversarial intelligence & red-team analysis, phase 3: implementation & iterative refinement and phase 4: comprehensive verification & completion.

github/awesome-copilot · 11 tokens

code-reviewer

Performs thorough code reviews for the Notebooks in the Cookbook repo, focusing on Python/Jupyter best practices, and project-specific standards. Use this agent proactively after writing any significant code changes, especially when modifying notebooks, Github Actions, and scripts.

anthropics/claude-cookbooks · 52 tokens