Claude writes most of Sonic Weaver. What makes it reliable is the setup around it: instructions, skills, workflows, memory and checks that catch its mistakes. Real examples inside.
Sonic Weaver is built by a very small team, and most of its code is written by Claude, Anthropic's AI, directed by our founder. People ask how that can produce a program with dozens of visualizer engines, two editors and a studio of workspaces without falling apart. The founder's answer is short.
Set your AI right and you can do anything.– Sonic Weaver's founder
This post is what "set right" means in practice. Every example below happened while we built this week's release, including the mistakes, because the mistakes are the point.
Anything is the goal, not a promise
The AI still gets things wrong, and every scenario here includes a wrong step. A good setup does not stop mistakes. It finds them before they reach you.
Every Claude session starts fresh, with no memory of your project. What it knows about how you work comes from what it is given: the instructions it reads first, the files it opens, and the tools it is allowed to use. The same model with a different setup gives very different results. Ours has six layers, from Claude down to the files on our own machine:
The order matters. Claude Code's own documentation says it plainly: instructions and memory are context Claude reads, not configuration it is forced to obey. So a rule that must hold cannot live only in the instructions. It has to be a check.
This week Claude gave every creation workspace on the site a launch link that an AI assistant can open already set up: the look chosen, the frame size set, the words filled in. A browser test opens each link and confirms the setup arrived. One case kept failing: Generate visualizer's starter look "never appeared".
The feature worked. Opening the link showed the right look chosen and the preview ready. The test was waiting for a part of the page that only appears on a different tab, so it could never pass. The AI had written a test that could not succeed, then spent time hunting a bug that did not exist.
The fix was the test, plus a rule we now apply to every new check: prove it fails on the defect it guards. The new test waits for the exact look the link named. Then we opened the page without that setting, and confirmed the test fails. A check that has never failed has never been tested.
Break it once
Before you trust a new check, break the thing it protects on purpose and watch the check go red. Then put it back.
SW Agent, the assistant built into Sonic Weaver, answers help questions from an index split into pieces, so a question loads only the few pieces it needs instead of everything. A test said a first answer reads at most six pieces. It had quietly started failing: the index had grown to 34 pieces, and the same question now touched seven.
The tempting fix is to change six to seven. That only lasts until the next help article. The real rule was never "six". It was "read only the pieces this question's words live in, and a small share of the whole". We wrote that instead, then proved it by making the search load one piece it did not need. The test caught it at once.
It had also been failing unnoticed, because it is not one of the checks every build runs. That is a second lesson in one: a test only protects you when something runs it. When an AI writes a limit, ask what the limit stands for, test that, and make sure the test is run.
We retired several older sites this year, and our instructions say not to present them as if they were live. A help article written last week still named one. Nobody would have spotted it by reading. A test that scans the pages we publish for AI assistants did, and the article was reworded the same day.
Another: seven features shipped last week without a line in the changelog. We keep a matrix of every system against every surface it must reach: its page, its help, its tests, the browser checks, MCP, SW Agent and the changelog. Anything missing is recorded as a known gap, with a reason and a date, and the list can only shrink. When a gap is closed but its line is left behind, the build fails too, so the list never lies. This week's release notes closed those seven gaps.
An instruction is something the AI should remember. A check is something it cannot forget.
This week three Claude agents worked side by side in separate lanes, on SW Agent's reasoning, on a calculator and geometry, and on new creator tools, while a fourth session did the integration. Each lane works in its own copy of the project, edits and runs focused tests. One session merges, builds, checks and ships, once.
We learned that shape the hard way. Earlier, several agents each started their own development server and ran the computer out of memory. Another time, merging the lanes broke three questions SW Agent used to answer correctly. The benchmarks caught the drop before release, because every build compares SW Agent's scores with a floor. The fix went in at the cause, in how SW Agent reads those words, and not by copying the test questions into what it learns from. That would have raised the score and made it a lie.
Every substantial job starts with a short written plan. It names the deliverable and one thing we will not do. It marks every value we assumed rather than read as an assumption, right beside the value. It runs first the cheap check that could end the job, such as whether the file exists or whether the policy allows it at all, before the expensive work. A question goes to the owner only when the answer changes what happens next.
The same thinking runs through the site, so you can use it too:
Set up like this, Claude gets through work that would take a team: this week alone, launch links for every workspace, release notes, new MCP tools and the checks that hold them in place. It still makes mistakes. The difference is that the setup finds them before you do.
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