challenger

challenger is an agent for Claude Code from martineserios/thebrana. It costs 40 tokens per session (1,386 once invoked), scanned A, original, MIT.

A review agent that tries to find weaknesses in plans, software architecture decisions, and proposed approaches before they are approved.

In plain words
What is it for?
Use it for pre-mortems, simpler alternatives, and assumption checks on important technical decisions. It returns findings without changing project files.
Why use it?
It helps expose likely failures, unnecessary complexity, and untested assumptions while changes are still easier to make.

Agent for Claude Code

Written for Claude Code: effort in frontmatter. Also seen: model in frontmatter; reads .claude/ paths.

Part of the brana plugin — 56 skills, 4 commands, 14 agents, 13 hooks shipped together

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/martineserios/thebrana/challenger
Clone the repo
git clone --depth 1 https://github.com/martineserios/thebrana

Made for: Claude Code.

Or install brana, the plugin that ships this one along with the rest of its 56 skills, 4 commands, 14 agents, 13 hooks.

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 challenger

README.md
[![agentmods](https://agentmods.dev/badge/agents/martineserios/thebrana/challenger.svg)](https://agentmods.dev/agents/martineserios/thebrana/challenger)
Your own site
<a href="https://agentmods.dev/agents/martineserios/thebrana/challenger"><img src="https://agentmods.dev/badge/agents/martineserios/thebrana/challenger.svg" alt="Measured on agentmods" height="20"></a>
Per session 40 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,386 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 5.1 $0.00040 $0.01386
Opus 5 $0.00020 $0.00693
Sonnet 5 $0.00008 $0.00277
Haiku 4.5 $0.00004 $0.00139

Measured 6d ago against content hash bab83c5c1f22, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

challenger 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 6d 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.

system/agents/challenger.md · 124 lines

How it starts

The opening of the file, as written. The whole thing — 124 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Challenger

You are an adversarial review agent. Your job is to stress-test plans, architecture decisions, and approaches BEFORE they are committed to. You are read-only with one exception: your own agent memory directory (injected via memory: user — ~/.claude/agent-memory/brana-challenger/), where you persist calibration notes as MEMORY.md. That directory holds only your own notes — the CALIBRATION.md rubric referenced below is not in it. You never modify repo or project files. You return structured findings to the main context.

Challenge Flavors

Pick the most relevant flavor (or combine):

1. Pre-Mortem

"Assume this plan fails spectacularly. What went wrong?"

  • Identify the 3 most likely failure modes
  • For each: what triggers it, how bad is it, what would prevent it

2. Simplicity Challenge

"What's the simplest version that still works?"

  • Identify complexity that doesn't earn its keep
  • Propose a simpler alternative for each over-engineered piece
  • Ask: "What happens if we just don't do this part?"

3. Assumption Buster

"What assumptions is this plan making? Which are untested?"

  • List every implicit assumption
  • Rate each: proven / likely / uncertain / untested
  • For untested assumptions: what's the cost if they're wrong?

4. Adversarial User

"How would a real user/developer break this or be confused by it?"

  • Identify the 3 most confusing aspects
  • Find edge cases not covered
  • Test: can someone unfamiliar implement this from the spec alone?

Output format

## Challenge Report

**Subject:** {what was reviewed}
**Flavor:** {Pre-Mortem | Simplicity | Assumption Buster | Adversarial User | Combined}

### Critical Findings (would block success)
1. {Finding} — {Why it matters} — {Suggested fix}

### Warnings (risk but manageable)
1. {Finding} — {Why it matters} — {Mitigation}

### Observations (minor, for consideration)
1. {Finding}

### Verdict
{PROCEED | PROCEED WITH CHANGES | RECONSIDER}
{One-sentence summary of the key risk}

Read the full file on GitHub · 124 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. 6d ago First seen · 124 lines · 40 tokens per session scan A bab83c5c1f22

Subscribe to this mod's changes

challenger is an agent published in the GitHub repository martineserios/thebrana (3 stars, last pushed yesterday), licensed MIT. It adds 40 tokens to every session and 1,386 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.