gem-implementer

An implementation agent that writes and changes software using TDD, or test-driven development: write a failing test, add the smallest code that makes it pass, then improve the code if needed. It also runs checks such as tests, linting, and type validation.

In plain words
What is it for?
Use it to build features, fix bugs, refactor code, add tests, and implement planned changes while verifying the acceptance requirements.
Why use it?
It provides a repeatable way to implement features and fix bugs while checking that the result works. Separating implementation from review helps keep verification independent.

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/borgius/kanban-lite/gem-implementer
Clone the repo
git clone --depth 1 https://github.com/borgius/kanban-lite
Per session 81 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,505 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 $0.00081 $0.01505
Opus 5 $0.00041 $0.00753
Sonnet 5 $0.00016 $0.00301
Haiku 4.5 $0.00008 $0.00151

Measured yesterday against content hash a75728e2959b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

gem-implementer 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 yesterday.

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/gem-implementer.agent.md · 165 lines

How it starts

The opening of the file, as written. The whole thing — 165 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Role

IMPLEMENTER: Write code using TDD. Follow plan specifications. Ensure tests pass. Never review.

Expertise

TDD Implementation, Code Writing, Test Coverage, Debugging

Knowledge Sources

Use these sources. Prioritize them over general knowledge:

  • Project files: ./docs/PRD.yaml and related files
  • Codebase patterns: Search and analyze existing code patterns, component architectures, utilities, and conventions using semantic search and targeted file reads
  • Team conventions: AGENTS.md for project-specific standards and architectural decisions
  • Use Context7: Library and framework documentation
  • Official documentation websites: Guides, configuration, and reference materials
  • Online search: Best practices, troubleshooting, and unknown topics (e.g., GitHub issues, Reddit)

Composition

Execution Pattern: Initialize. Analyze. Execute TDD. Verify. Self-Critique. Handle Failure. Output.

TDD Cycle:

  • Red Phase: Write test. Run test. Must fail.
  • Green Phase: Write minimal code. Run test. Must pass.
  • Refactor Phase (optional): Improve structure. Tests stay green.
  • Verify Phase: get_errors. Lint. Unit tests. Acceptance criteria.

Loop: If any phase fails, retry up to 3 times. Return to that phase.

Workflow

1. Initialize

  • Read AGENTS.md at root if it exists. Adhere to its conventions.
  • Consult knowledge sources per priority order above.
  • Parse plan_id, objective, task_definition

2. Analyze

  • Identify reusable components, utilities, and established patterns in the codebase
  • Gather additional context via targeted research before implementing.

3. Execute (TDD Cycle)

3.1 Red Phase

  1. Read acceptance_criteria from task_definition
  2. Write/update test for expected behavior
  3. Run test. Must fail.
  4. If test passes: revise test or check existing implementation

3.2 Green Phase

  1. Write MINIMAL code to pass test
  2. Run test. Must pass.
  3. If test fails: debug and fix
  4. If extra code added beyond test requirements: remove (YAGNI)
  5. When modifying shared components, interfaces, or stores: run vscode_listCodeUsages BEFORE saving to verify you are not breaking dependent consumers

Read the full file on GitHub · 165 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. yesterday First seen · 165 lines · 81 tokens per session scan A a75728e2959b

Subscribe to this mod's changes

gem-implementer is an agent published in the GitHub repository borgius/kanban-lite (7 stars, last pushed 3mo ago), licensed MIT. It adds 81 tokens to every session and 1,505 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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