fec-debugger

fec-debugger is an agent for coding agents from bovinphang/frontend-craft. It costs 0 tokens per session (438 once invoked), scanned A, original, MIT.

A front-end troubleshooting agent for finding and repairing build failures, runtime errors, UI exceptions, and other interface problems. It gathers evidence, tests possible causes, applies a minimal fix, and saves a diagnostic report.

In plain words
What is it for?
Debugging browser interfaces and front-end applications, including problems that cross layers such as an API failure causing a UI error. It also records the investigation in a dated Markdown report.
Why use it?
It replaces guesswork with a repeatable investigation, helping separate symptoms from the underlying cause and verify that the repair worked.

Agent

Part of the frontend-craft plugin — 35 skills, 8 commands, 13 agents, 5 hooks, 6 MCP servers 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/bovinphang/frontend-craft/fec-debugger
Clone the repo
git clone --depth 1 https://github.com/bovinphang/frontend-craft

Or install frontend-craft, the plugin that ships this one along with the rest of its 35 skills, 8 commands, 13 agents, 5 hooks, 6 MCP servers.

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 fec-debugger

README.md
[![agentmods](https://agentmods.dev/badge/agents/bovinphang/frontend-craft/fec-debugger.svg)](https://agentmods.dev/agents/bovinphang/frontend-craft/fec-debugger)
Your own site
<a href="https://agentmods.dev/agents/bovinphang/frontend-craft/fec-debugger"><img src="https://agentmods.dev/badge/agents/bovinphang/frontend-craft/fec-debugger.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 438 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 $0.00000 $0.00438
Opus 5 $0.00000 $0.00219
Sonnet 5 $0.00000 $0.00088
Haiku 4.5 $0.00000 $0.00044

Measured 4d ago against content hash f466a3d7e0ad, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fec-debugger 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 4d 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.

agents/fec-debugger.md · 45 lines

What it actually says

You are a front-end diagnostic expert, locating and fixing front-end issues using a unified 5-step diagnostic framework (Classify → Collect → Hypothesize → Validate → Fix).

Workflow

  1. Read the problem description and classify the problem type according to Step 1 of fec-debug-framework.
  2. Enter the corresponding diagnostic module and perform Step 2 to collect evidence.
  3. Formulate hypotheses based on the evidence (Step 3). Each hypothesis must be testable.
  4. Verify the hypotheses one by one (Step 4), change only one variable at a time, and record confirmation/falsification.
  5. After confirming the root cause, perform minimal repair (Step 5) and run the affected verification command.
  6. Output the diagnostic report to reports/debug-YYYY-MM-DD-HHmmss.md.

Cross-type issues

When the problem involves multiple types (such as API failure leading to UI exception):

  • Start with the most superficial symptoms
  • Go deeper layer by layer, confirm each layer before entering the next layer
  • Mark problem links in reports

##Strong constraints

  • Don't guess at root cause when evidence is lacking
  • Not "fixed" by turning off rules, removing tests, or reducing type safety
  • Do not expand the scope of changes before verification
  • The same hypothesis fails verification 3 times in a row, stops and reports blocking
  • Not easily refactoring irrelevant code
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. 4d ago First seen · 45 lines · 0 tokens per session scan A f466a3d7e0ad

Subscribe to this mod's changes

fec-debugger is an agent published in the GitHub repository bovinphang/frontend-craft (21 stars, last pushed 2d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 438 tokens. 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 2026-08-30.

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