Cursor for PHP Legacy Code: Can Agents Work Safely?

CalebCodeTrail:

Start by using the agent for investigation rather than implementation. Ask it to map request entry points, database access, shared includes, global variables, and side effects. Then request a written plan that names the files it expects to change. This helps you catch incorrect assumptions before code is modified. For the first few tasks, allow only one narrowly defined fix at a time. Review the diff, run the affected workflow manually, and commit the approved change separately. Small tasks make unexpected behavior easier to identify and reverse.

BrooklynPatchWorks:

A legacy application often depends on undocumented behavior. A function that looks redundant may support an old report, scheduled task, browser, or integration. Tell the agent not to remove code merely because it appears unused. Require evidence such as references, logs, tests, or a controlled search before deletion. I would also prohibit broad formatting changes during functional work. When hundreds of lines are reformatted, the meaningful changes become harder to review and accidental edits are easier to miss.

SeattleScriptRunner:

Create project instructions that describe the actual runtime constraints. State the supported PHP version, database engine, framework version, coding style, deployment method, and directories that must not be edited. Include rules such as "do not introduce syntax newer than PHP 7.2" or "do not modify generated vendor files." Persistent instructions reduce repeated prompting, although they do not replace review. After updates to Cursor or its available models, confirm that your rules are still being followed as expected.

HannahTestsFirst:

The largest safety improvement is adding tests around existing behavior before asking for refactoring. These can be modest characterization tests that record what the system currently does, even when that behavior is not ideal. For database-heavy pages, create a test database with representative but non-sensitive data. If full automation is unrealistic, document a repeatable manual checklist for login, permissions, inserts, updates, reports, email triggers, and scheduled jobs. An agent needs observable pass or fail signals; otherwise, it may produce code that looks cleaner while changing important behavior.

MarcusBranchGuard:

Never let the first experiment happen on your main branch or production working directory. Use a clean branch, confirm that the repository has no uncommitted work, and create a recoverable checkpoint before the agent edits anything. Inspect both the file diff and the list of changed files. A correct-looking patch in one file may be accompanied by an unwanted configuration, dependency, or migration change elsewhere. Keep deployment as a separate human-controlled action rather than allowing an editing session to publish automatically.

DesertQueryFixer:

Be especially careful with direct SQL queries. An agent may correctly improve syntax while overlooking transaction boundaries, character encoding, duplicate handling, triggers, or application-specific permission checks. Ask it to preserve query behavior unless the task explicitly requires a change. For write operations, test rollback behavior and row counts. Avoid giving an agent unrestricted production database access. A local or isolated database account with limited privileges provides a safer environment for testing generated commands.

CarolineSecureBuild:

Review the repository before indexing or sharing context. Exclude environment files, private keys, backups, database exports, customer uploads, and production logs that contain sensitive data. Also inspect third-party or unfamiliar repositories before allowing an agent to execute instructions or terminal commands from them. Repository content can influence agent behavior, so files should not automatically be treated as trusted instructions. Keep command approval enabled and read every destructive, network-related, installation, or permission-changing command before it runs.

NashvilleModuleMaker:

I would not begin with a whole-application modernization. Choose a boundary such as one report, import routine, validation function, or service class. Ask the agent to add tests, document dependencies, and make one compatible improvement inside that boundary. Once the team understands the review workload and failure patterns, expand the scope gradually. The time saved by generating a large refactor can disappear quickly if reviewers must reconstruct several undocumented business rules at once.

ErinRuntimeCheck:

Static inspection is not enough for older PHP. Run the code with the exact production PHP version or a faithful container or virtual machine. Newer development environments may accept functions, syntax, extensions, or database behavior that the real server does not support. Add a syntax check, application tests, and representative browser requests to your workflow. Also inspect warnings and notices, because legacy applications sometimes hide them even when they reveal a newly introduced compatibility problem.

AustinDiffReader:

My rule is that the agent can prepare the change, but a person must own the result. The reviewer should understand why each affected line changed, confirm that authentication and authorization checks remain intact, and verify that error handling still matches the application's conventions. For low-risk cleanup, review may be quick. For payment, identity, permissions, file deletion, or production data paths, require deeper testing and possibly a second reviewer. Safety depends more on the surrounding process than on the prompt alone.