Your coding agent needs eval gates before it ships (or you'll debug its hallucinations forever)

Your coding agent just told you it "successfully implemented the user authentication system" and pushed three files. You check the PR. The login function returns true for any password. The session management is a TODO comment. The database migration is missing.

This is the silent failure problem. Your agent thinks it shipped. You think it shipped. Nobody knows it's broken until a user tries to log in.

The solution isn't a smarter model. It's eval gates — structured quality checks that run before your agent calls anything "done."

The eval gate pattern works like this:

• Agent completes a task
• Before reporting success, it runs a series of pass/fail checks
• Only if all checks pass does it mark the task complete
• If any check fails, it goes back to work

Here's what a basic eval gate looks like for a coding task:

EVAL_GATE_CODING = """
Before marking this task complete, run these checks:

1. COMPILE_CHECK: Does the code compile/run without errors?
2. REQUIREMENT_CHECK: Does the implementation match all specified requirements?
3. TEST_CHECK: Do existing tests still pass? Are new tests needed?
4. INTEGRATION_CHECK: Does this work with the existing codebase?
5. EDGE_CASE_CHECK: What happens with invalid input, empty data, or errors?

For each check, respond with PASS or FAIL and explain why.
If any check fails, continue working. Only report completion when all checks pass.
"""

The magic happens when you make these checks specific to your domain. A web scraping agent needs different eval gates than a database migration agent.

For API integrations, I use this gate:

1. RESPONSE_CHECK: Does the API return expected data structure?
2. ERROR_HANDLING_CHECK: What happens when the API is down/rate limited?
3. AUTH_CHECK: Are credentials handled securely?
4. PAGINATION_CHECK: Does it handle multiple pages of results?
5. LOGGING_CHECK: Can we debug this when it breaks?

For database work:

1. MIGRATION_CHECK: Does the migration run without errors?
2. ROLLBACK_CHECK: Can we undo this change safely?
3. INDEX_CHECK: Are queries still performant?
4. CONSTRAINT_CHECK: Do foreign keys and validations work?
5. DATA_INTEGRITY_CHECK: Is existing data still valid?

The key is making your agent actually run these checks, not just think about them. For the compile check, it should literally try to run the code. For the test check, it should run the test suite.

Pro tip: Add a "HUMAN_CHECK" gate for high-stakes changes. "Does this change require human review before deployment?" Your agent should know when it's out of its depth.

I've seen agents catch their own bugs with eval gates that I would have missed in code review. The authentication example above? An eval gate would have caught it immediately when the REQUIREMENT_CHECK failed.

The pattern works because it forces your agent to be its own worst critic before declaring victory. No more "successfully implemented" lies. No more debugging hallucinated completions.

Your coding agent should ship working code, not creative fiction about working code.