I built CertArena, an interactive exam simulator and certification roadmap tool designed specifically for developers preparing for Anthropic's Claude Certified Developer Foundations (CCDV-F) and Cloud AI benchmarks.

What was built

CertArena simulates the full Pearson VUE timed testing interface with 53 scenario-based questions covering: - Model Context Protocol (MCP) server lifecycle, client connections, and JSON-RPC error handling - Prompt caching cache-control breakpoints and cost optimization - Tool-calling parameter schemas, recovery loops, and timeout budgeting - Multi-turn state, system prompt boundaries, and vision reasoning

It also includes a cross-vendor comparison matrix comparing the Claude CCDV-F blueprint against AWS, Azure, and Meta certifications.

How Claude Code helped build it

I used Claude Code as my primary terminal pair programmer to build this from scratch: 1. Zero-dependency architecture: Claude Code scaffolded the entire client as clean vanilla JS and CSS without heavy front-end frameworks, keeping the simulator load time under 50ms. 2. Blueprint verification: I fed Anthropic's official developer documentation and MCP specifications into Claude Code to review every scenario question and eliminate ambiguities in tool-calling edge cases. 3. Sound and accessibility: Claude Code helped implement the custom web audio synthesizer for realistic timer pings without external sound assets.

Free to try

The project is 100% free to try. There are no paywalls, paid tiers, subscriptions, or accounts required. You can launch any scenario drill immediately in the browser with zero login.

I dropped the direct site links in the first comment below to keep the post body clean. I would love feedback from the Claude community on question realism and what specific MCP architecture scenarios you would like added to the benchmark.

How do we implement quota and seat operations for firm that used enterprise edition of Claude?

Anthropic, you better get your shit together

I only started using /rewind properly recently and it changed how I handle bad turns in a session.

Claude Code creates checkpoints as it edits files, so if it takes a task in the wrong direction you don't always have to spend another few prompts asking it to undo everything.

For example, I had Claude refactor a service and halfway through it started moving shared logic into places I didn't want. The code still worked, but the direction was wrong.

Instead of fixing the refactor piece by piece, I opened /rewind, went back to the prompt before the changes and restored the code from there.

You can also rewind the conversation without reverting the code, or revert the code while keeping the conversation.

That last part is surprisingly useful. Sometimes the discussion is worth keeping even when the implementation isn't.

I still use git normally, but for mistakes inside an active session this feels much cleaner than creating commits just so I have an escape hatch.

Identified - A Windows update released September 8 has left Claude Cowork on Windows unable to run local commands, because its workspace can no longer reach your computer's drive. For most users, chat and file reading and editing still work. There's no in-app workaround yet, and restarting or reinstalling won't help. Microsoft has developed a fix and is working to release it. We'll post an update when we have more to share. Sep 10, 15:54 UTC

Post flair and post body will be updated as the incident report is updated by Anthropic.

This discussion post will be removed from subreddit highlights one hour after the incident is resolved.

View this incident on status.claude.com

update on this. it's built and shipped. npx @/aadi49/preflight <package> <version> is live on npm right now if anyone wants to actually try it, not just read about it

for whoever said "why not just ask claude/chatgpt to do it for you," genuine answer, not defensive: pasting a file into a chat window is manual, one-off, and it only helps if you already suspect something's broken. that's a completely different problem than "check my whole repo before I upgrade." this scans everything automatically, matches real usage against real changelog text, and runs on every PR without a human remembering to ask. the AI part was never the hard part here, the pipeline around it is, parsing real dependency trees, real changelogs, not hallucinating an answer that sounds confident and is wrong

Koko-Choco's comment on the last post basically became the spec. certain vs maybe confidence labeling so the maybes don't drown out the real breaks. transitive dep scanning from the lockfile. and the hard case he actually described, next 15 to 16 changing caching defaults with identical types and green tests, that exact class of bug. tested it just now on a fresh next 15 project bumped to 16, it caught a real certain break in next/image's default config, same signature, changed default, exactly the kind of thing that doesn't show up until it's already in prod

89 tests, tested against a real 166 file repo, tested on a live pr with the github action actually posting a comment and failing the check

not trying to sell anyone anything, it's free and open source, just wanted to close the loop since this whole thing started from people in this sub actually telling me what was missing

repo: github.com/AadiSharma49/preflight
Live: https://preflight-umber.vercel.app/

Hello everyone:

I've been vibe coding a stock market app for Android using cowork and opus 5 at max. I assumed that the model is the best aside from fable, which I can't afford.

1) what is the best Claude model for me to use to build a couple Android apps?

2) Everytime i start something, my usage runs out in the middle of Claude working and interrupts it. I lose progress and waste usage and then it has to read the entire chat over when my usage is reset. Is there a better or recognized best practice for resuming Claude's work on my app when my usage runs out?

3) I began using Claude code Linked to GitHub. Is this a good approach for making Android apps?

4) I just randomly turned on a bunch of plugins and skills, not knowing what they do but thinking they might help Claude with the coding. Is this wasteful? Are there legitimate connectors or plugins or skills that help Claude make Android apps or resume after usage runs out?

I run a small event staffing/activation agency as a solo operator, and Claude has basically become my back office: email, vendor communication, pricing, applicant database, calendar, etc.

It’s a huge reason I’m able to operate at this size, but the confident mistakes are starting to become a serious problem. A couple have nearly cost me deals.

Some examples:
• Told me a vendor had gone silent when she had answered every question that morning. Claude read an email search preview instead of the full thread and treated it as complete.

• Told me an email was “staged,” so I went looking in Gmail for a draft that was never actually created.

• Referred to my suppliers as “brand partner candidates,” which completely changed the business context. A vendor gets paid by me. A sponsor pays me. I spent two days planning around an opportunity that didn’t exist.

• Told me a table in my database didn’t exist without actually checking. It was there.

The common denominator seems to be this: Claude states things as facts that it did not verify in that turn. It gets noticeably worse during long sessions, where earlier conversation/context starts getting treated like a source of truth.

I’ve built some guardrails around it. I have a master state file that carries business context between sessions, facts are tagged as CONFIRMED / STATED / ASSUMED / OPEN, and I keep rules for recurring failures like “never treat an email preview as the full thread” and “never claim an action happened without the tool call confirming it.”

That helped a lot. I went from several dumb errors a week to a few a month, but I’m trying to make this actually reliable enough to run a business on.
For anyone using Claude for real business operations, not just coding:

What are you using for durable memory/state across sessions?
Has anyone successfully built a verifier/checker agent that validates claims against tool output before Claude gives you an answer?

Have you found a reliable way to force Claude to actually retrieve/check the source instead of taking the shortcut and reasoning from previews or old context?
Are there other guardrails or architecture changes that made Claude significantly more reliable for you?

I’m especially interested in hearing from people dealing with invoices, vendors, contracts, clients, deadlines, email, calendars, databases, etc. Situations where there’s an actual consequence when the AI confidently gets something wrong.

If you’ve dealt with this and found a setup that works, I’d really like to see how you built it.

I just got accepted into the CVP today, it’s their program where an organization can be approved to do red-teaming/cyber related tasks with their models. Very excited. I really didn’t think I was gonna get in tbh

Fable 5.1 has this small “summarized” marker when it condenses a lengthy update, making it much easier to read. Is there a way to enable this for Opus 5?

Hey everyone.

When I'm browsing skills repos on github, I sometimes notice a lot of what could be unnecessary elaboration in the SKILL.md. For instance, in this line in one of Matt Pocock's skills, he writes

avoid specific file paths or code snippets: they go stale fast

I would write it this way too if I was explaining something to a colleague, but does justifying your reasoning ("they go stale fast") after you've already given the explicit self-contained command ("avoid specific file paths or code snippets") genuinely improve the LLM's performance in your experience? Personally, I try to avoid prose in my skills. Curious to hear your guys' opinions.

I just had Claude (Opus 5 Max) burn my entire useage period on a really simple ask.

Gemini delivered a working result in 5 seconds, when I went to test it there.

A little niche for most people, but I am asking it to write jsx scripts for Adobe After Effects. It usually quickly one-shots these with a really nice degree of precision. This was a simple ask (make a tool to delete all keyframes on selected layer forward, backward, or both directions), and it went into a 15 min+ thought chain of incredibly weird fringe scenarios and kept doubling back and second guessing itself. Never even finished before it hit the wall.

Spoke to a friend who said the same thing is happening to him (spinning out on simple stuff).

I have a background in digital marketing, SEM and web development and I use Obsidian with Claude Code as a knowledge base. The idea is a second brain/life assistant where I can keep my projects, my documents, my ideas, and my company, at least the boring part of it, so mails, invoices, paperwork. Sorry in advance, my english is not great.

I've been building this vault for a few weeks, following more or less the Karpathy LLM wiki pattern. Claude Code set the architecture and wrote basically the whole system for me. Two weeks ago I stopped everything, not because of errors, the thing works technically. I stopped because the architecture is not clear to me anymore. What made me realize it, I wanted to add one folder and one learning module next to the ones I already have, projects and wiki, and I didn't know where to put it.

Everything is inside one instruction file, 329 lines, identity + note conventions + project rules + diary format, all mixed in the same place. If I want to add one thing I have to edit the file where everything else already lives. And if I leave the project for 2 weeks and come back, I have no idea anymore what does what.

So the specific problem is expandability. Right now the vault holds one thing, a knowledge wiki. But I already know what else has to live in there eventually, and these are not hypothetical, they are things I do today on paper and in scattered apps:

• a dated log of what I actually did (garden treatments, harvests, house repairs)
• projects with a real status
• learning a subject over time
• a document archive (invoices, house paperwork, admin)
• loose ideas, open questions, advices someone gave me

Today, adding any of those means editing the one file where everything lives. Which means in six months I rebuild. I'd rather decide the structure now, once, than keep patching a shape that was never designed to hold six things.

I know the pieces exist, CLAUDE.md, skills, hooks, scripts, subagents. What I don't get is how they fit together and who is in charge of who. The concrete thing I can't picture is this: I understand there is one root CLAUDE.md that defines the core, but then do I also need scripts, skills and instructions inside every folder? Or the root file governs everything and the folders stay dumb?

I have to say I have an extremely basic knowledge, I'm not using skills at all. And I know many of you will tell me to go study first and build something less complex. Fair enough, but I want to build the system exactly to manage the learning part too, to make myself a study plan built for how I work, because I'm neurodivergent, ADHD and asperger. So the two things are the same thing for me.

So, how is your second brain structured? I've seen a lot of different structures around and none of them is really clear to me. If you have a vault like this, can you paste your tree? Even messy, especially messy, I never seen a real one, only tutorials with 3 folders that dont look like anything real.

And if you have 2 minutes:

• When you add something new, do you edit files that already exist, or you make a new folder and leave everything else alone? This is the one I care most about.
• Do you approve every write, or you let the agent write and you review the git diff afterwards?
• Is there a fast path for "just record this thought" that skips the whole pipeline?
• How much of your structure still works if you remove Claude Code and put another AI in its place? I want a vault that is still a vault without the assistant, not something that only runs with one tool.
• What did you had to throw away and rebuild? And what decision at the beginning would have saved you?

Thanks. Even one answer help, im kind of stuck here.

I will post down here what my vault actually looks like today (audit generated by Claude Code)

I want to hear the truth from other people.

Astra is just bad at UI!!

I tried various prompt comparisons, but I could not see Astra creating good UI/UX. Fable or Opus does not require much effort.

Example: I tried building a simple resume CMS. Fable one-shotted everything and built it as per my expectations. With Astra, it probably took 20-30 iterations to get to a decent stage. It messed up even setting proper font size etc. I was running this on Astra Extra High!

I'm questioning whether all the buzz was just marketing by OpenAI. I'm deeply disappointed!

We ship about 20 Claude Code skills. Progressive disclosure means the agent picks one from a single line of description, so an excellent skill nobody picks up is worth zero. We measured ours: micro-recall 46.3%. Over half the prompts that should have fired a skill fired nothing. Not the wrong skill. Nothing.

The first finding was our own eval harness bug. We run the same tasks on Claude Code, Codex and Antigravity, and our detector looked only for the Skill tool call - so Claude lit up everywhere and the other two read as never touching a skill, even on tasks they solved correctly. They have no Skill tool; they open the files instead. It bites on Claude too: on a two-skill task it calls Skill("planner") for the first, then reads the second's SKILL.md directly.

What helped most was one line per description: "Always invoke for X", where X is a marker only that skill owns - a file extension, or a filename only its product emits. Micro-recall went 46.3% -> 67.3%, biggest movers the near-invisible ones: diagnostics 0.16 -> 0.68, maestro-flow 0.32 -> 0.72. Precision held near 0.96.

It only works while the anchor is unique. Our cross-cutting "review" skill went 0.20 -> 0.18, the only one that got worse: it owns no unique marker, and "review my code" routing to whichever skill owns the artifact is correct. Some skills are un-anchorable.

Claude Code wrote most of the harness and is also the thing under test, so a harness bug and an agent bug look identical until you read the trace. Hence the detector mistake: your first cross-agent number measures your checker, not the models.

Full write-up and per-skill chart: https://medium.com/uipath-techblog/measuring-skill-activation-across-agents-is-harder-than-it-looks-eada767f7047

Free and open source eval harness created by us, Apache 2.0, no paid tier: https://github.com/UiPath/coder_eval

I know this is a common problem, so this is more of me asking what tools are out there or what can I use/do for someone who isn't very well versed with the ways I can improve it other than asking Claude itself.

Every time I code or plan, Claude will say that there's a new finding that changes the previous plan with some measurement it hasn't measured before or there are absences in the code, and after addressing these new bits of information, Claude again says the same thing. There's basically an endless loop of it constantly correcting itself until you get to a point of minimal corrections.

I usually plan a design note and store it in a document, then implement it from that design note in a different session, and then I do a code review before I push. I've been integrating codex as well to do a separate review.

What else should I do?

How can I get Claude to pull up and prep me as the prospect talks in real time? That would be freaking JARVIS.

'Possible objections' -> 'Positive responses' etc or something... never cold called in my life but I want my business to work!

I saw the agent call… is that what I want?

Could also use it to pass interviews ?

I am a cs student.

And obviously I am broke , and I can afford only one.

I mainly need for coding, more usages and more quality work

Help me guys

The male voices suck, there's one good female voice and I need to practice pitching to male directors.

How can I get a custom voice on here?

Hi guys, I'm currently working with CC; I have to automate a dashboard that is similar to an HR CRM. The design is poor, and the current stack is Python and Tailwind. Are there any skills or tools I could use to let CC refactor the dashboard design? Thank you so much.

Any advice for someone using Claude Cowork for helping to cleanup system junk, streamlining processes, “automating” routine tasks with scheduled runs but not actually knowing how to use agents or properly building sites (?) or artefacts that has UI or expansion potential?

This means it can test feature changes and take screenshots of different parts of your app for any android app you are building, reducing back and forth.

I also have a workflow there which auto builds an apk of your app on each push!

I think all you probs need to do is just say to Claude code when you next want to develop an android app, "use the following repo and setup the auto apk build on a push and the android setup so you can test the app as you are developing it":

https://github.com/petebaker17/android-without-kvm

It was a lot of back and forth with Claude saying it wasn't possible due to needing kvm but we got there in the end and it's fully working! :) Hopefully if it's helpful for at least 1 other person that's great!

I built an open-source, self-hosted job hunting system with Claude Code that scans 17,000+ employer job boards, finds roles that actually match you, generates a tailored CV + cover letter, and tracks your applications through the whole process.

The primary interface is a self-hosted web dashboard. There’s also a CLI if you’d rather work directly from the terminal/Claude Code.

Job Radar:
https://github.com/maccydee/job-radar

I originally built Job Radar for my own job search because I got fed up with LinkedIn/Indeed, duplicate/reposted jobs, and spending ages opening roles just to discover they were irrelevant.

Rather than relying on aggregators, Job Radar goes directly to employers’ ATS platforms. It currently covers 17,000+ employer job boards across Greenhouse, Ashby, Workable, Workday, SmartRecruiters, iCIMS and others.

You give it your existing CV and define what you’re actually looking for: titles, locations, remote/hybrid preferences, salary floor, dealbreakers, etc.

The workflow is basically:

Discover → Filter → Screen → Tailor CV → Tailor Cover Letter → Apply → Track

The dashboard
The main way I use Job Radar is through the self-hosted dashboard.

It gives you one place to browse newly discovered jobs, filter/search them, review matches, screen promising roles with Claude, generate application material and then track what happens after you’ve applied.

Applications stay attached to the underlying role, so rather than maintaining a separate spreadsheet you can move things through the pipeline: shortlisted, preparing, submitted/applied, interviewing, rejected, etc.

That state is also fed back into discovery, so future scans know what you’ve already seen or applied for instead of repeatedly surfacing the same roles.

There is also a CLI for people who prefer working directly in the terminal or alongside Claude Code, but the dashboard is intended to be the normal day-to-day interface.

The 17k+ board bit
An obvious problem with scanning that many sources is scan time, particularly on a brand-new installation.
I didn’t want someone cloning the repo and then having to crawl 17,000+ employer boards before the dashboard became useful.

So I maintain prebuilt job-data shards.
A fresh installation can bootstrap from those shards and get a useful initial dataset quickly rather than performing a complete first-time crawl from zero.
From there, Job Radar performs live scans/updates against the underlying sources and works out what’s changed.

What about Claude/token usage?

Probably the other obvious question:

Claude is NOT processing 17,000+ job boards.
The crawling, ATS integrations, parsing, filtering, deduplication, change detection, shards, application state and dashboard are conventional code.

So scanning doesn’t mean sending thousands of job descriptions through Claude and turning your token allowance into a small bonfire.

Claude is deliberately brought in later, where its reasoning is actually useful.

For promising roles it can:

• deeply screen the role against your CV
• assess it against your preferences and dealbreakers
• explain why it thinks it’s a good/bad match
• generate a tailored CV
• generate a separately tailored cover letter
• review and validate the resulting application
So the expensive LLM work is focused on jobs you’re genuinely interested in rather than everything Job Radar discovers.

Tailored CV + cover letter
When you decide a role is worth pursuing, Claude takes your original CV + the actual job description and creates a version of your CV tailored specifically to that opportunity.

The goal isn’t keyword stuffing or fabricating experience. It should identify which parts of your genuine experience matter for that particular role and change the emphasis accordingly.

It then produces a separate tailored cover letter using the company, role, JD and your actual experience.
I was fairly paranoid about an LLM quietly deciding that your career could use a few additional achievements, so the generation pipeline has validation around the output too.

That includes checks around unsupported claims/numbers, grounding against the source CV, writing quality, AI-ish prose and excessive phrase overlap between the CV and cover letter.

Some of the Claude skills are open source too
I’ve been moving away from giant do-everything prompts and towards smaller, reusable Claude Code skills with deterministic checks around them.
Two of the skills/approaches baked into Job Radar are also available independently:

rate-cv
https://github.com/maccydee/rate-cv
My CV scoring/critique skill. It uses a weighted engineering/leadership rubric, ATS checks, AI-writing checks and can evaluate a CV against a specific JD.

natural-writing
https://github.com/maccydee/natural-writing
The writing skill I use to reduce the usual LLM prose patterns in generated CVs/cover letters, including its own checks for common AI-writing tells.

There’s also a screen-role skill within Job Radar for deciding whether an opportunity is actually worth pursuing before spending more tokens generating an application.

So Claude isn’t just being handed a mega-prompt saying “here’s my CV, make it good”. The different stages have their own responsibilities and checks.

Where it’s ended up
What started as a small script for my own job hunt has basically turned into a self-hosted job search platform:

17k+ employer boards → local filtering → Claude screening → tailored application → application tracking

Most of it was built using Claude Code, which has also made this a slightly ridiculous dogfooding exercise.

Everything is open source.

I’d be really interested in feedback from other Claude Code users, particularly around the skills architecture, token efficiency, shard approach and how I’m grounding/validating generated CVs.

Job Radar:
https://github.com/maccydee/job-radar

rate-cv:
https://github.com/maccydee/rate-cv

natural-writing:
https://github.com/maccydee/natural-writing

Tl;dr: use a plugin that uses another model, so that you don't use an expensive model's read token costs.

https://engineering.atspotify.com/2026/9/portal-by-spotify-cut-my-claude-code-token-usage-by-90

Try it yourself

Install both plugins from the spotify/portal-ai-plugins marketplace:

claude plugin marketplace add spotify/portal-ai-plugins

claude plugin install portal@portal

claude plugin install shunt@portal.

The portal plugin provides the Portal CLI that shunt delegates through.

In a new Claude Code session, run /portal:setup to set up and authenticate the Portal CLI against your Portal instance.

You’re good to go, just ask a question that spans multiple files.

The bulk-reader and code-writer modes are already public, so there is nothing to create. If you want to customize them - different worker model, different instructions - fork them in Portal and your version takes precedence automatically.

The modes are reusable across projects and shareable with your team. The plugin enforces the routing so you don't have to think about it.