Claude runs five of the seven checks on Claude-written code at Anthropic

A fuzzer is worth running when it finds inputs nobody would write by hand. The dev.to post says a Claude-powered fuzzer "likely" does one of two things: read a function signature and generate cases for null inputs, boundary values and type mismatches, or mutate existing inputs with knowledge of their structure, so that a JSON or SQL payload comes out plausible but malformed ^[5]. Both of those are semantic test generation. The post marks its own description as inference.

It also names the failure mode. If Claude generates test cases that always pass, the fuzzer becomes a false sense of security, and a separate validation layer is needed to confirm it is finding bugs and not green checkmarks ^[6]. I would build that validation layer before the fuzzer. Running daily means new functions get new cases and refactored code gets re-fuzzed ^[12], so the suite grows whether or not its finds are real.

The split between the two review passes is the one design choice with a stated reason. Per the post, the threat models differ. A code review asks whether the logic is clear, whether names are descriptive, whether a function does one thing, and whether there are off-by-one or null dereference errors ^[8]. A security review asks whether an attacker can inject SQL or shell commands, whether authentication checks can be bypassed, whether sensitive data leaks into logs, and whether rate limits are enforced ^[8]. Two passes let each one carry its own prompt, its own examples and its own escalation rules ^[15].

The post says Anthropic did not state whether a Claude-flagged security issue blocks the merge, notifies a human, or gets rewritten and re-submitted automatically ^[7]. The severity ladder it offers is its own guess ^[7]. The ordering claims sit in the same category: that each layer operates independently, and that the refactoring step does not run until a flagged SQL injection risk is fixed, are the post's construction ^[4].

Anthropic's own account of this is one sentence and six nouns ^[1][2]. Five of the seven stages in the post's pipeline are model calls ^[13]. The list transfers to another team only if their existing tests are good enough that an agent-written end-to-end suite adds cases instead of restating them. The second condition is that the two review prompts differ enough that the security pass catches what the code pass approved. Someone also has to own the question of whether the fuzzer's finds are real. The final stage, in the post's telling, is one Claude instance flattening another's five levels of nested if statements into early returns or guard clauses ^[11].