agent hit the target's rate limit and the scan stalled mid-engagement

TL;DR

When the target starts answering with rate-limit responses or resets, an agent that keeps its full request rate just extends the ban and stalls the whole run. Detect the throttling signal, back off exponentially, drop to the rate the engagement agreed, mark throttled targets as deferred with their remaining work, and continue elsewhere in scope instead of freezing the engagement.

agent hit the target's rate limit and the scan stalled mid-engagement

Use this when

• Responses shift to HTTP 429, connection resets, or a WAF block page partway through scanning one authorized target.
• The agent run shows no progress while its logs fill with retries against the same host.

Not for this skill when

• The client asked for testing to pause or the target is a fragile production system struggling under load. Stop and escalate; pacing is not permission to continue.
• A single slow target with no throttling signals. That is latency, handled by timeouts and checkpoints.

Steps

1. Detect the signal explicitly: count 429s, resets, and block-page signatures per target in the runner, instead of treating them as generic errors. Verify: Verify: the run state names this target as throttled, with the signal counted.
2. Back off before retrying: wait an increasing interval, and notify the run log, rather than immediate retries at full rate. Verify: Verify: retry timestamps show the backoff intervals.
3. Reduce the tool rate for this target to the requests-per-second the rules of engagement state, and resume its remaining checks at that rate. Verify: Verify: the tool invocation for the resumed work carries the reduced rate settings.
4. If throttling persists, defer the target: write its unfinished checks to the run manifest as deferred-throttled, and move the agent to the next in-scope target. Verify: Verify: the agent makes progress elsewhere and the deferred work is listed, not forgotten.
5. At the end of the run, schedule the deferred targets once more at the gentlest rate, and report any still unfinished as a coverage limitation with the throttling evidence. Verify: Verify: the final report names the deferred targets and why.

Variant phrasings

pentest agent 429 backoff deferred target manifest

The handling-design phrasing.

waf throttles scanner agent scan stalled mid engagement

The symptom phrasing.

agent keeps retrying rate limited host full rate

The anti-pattern phrasing.

Compatibility: Compatibility: any agent harness wrapping rate-aware tools; requires the agreed request rate from the rules of engagement to pace against.

Why it happens

Rate limits are a target telling you the rules changed. Agents without a throttling concept read 429s as transient errors and retry harder, which deepens bans and can lock out legitimate users or the test account. A stall is often the agent waiting on a target that will not answer it for a long while, while other in-scope work sits untouched behind it in the queue.

Edge cases / pitfalls

• Never treat throttling as an invitation to rotate source addresses or otherwise evade the control; that crosses from testing into evasion and breaks engagement trust.
• Distinguish the target's limit from a shared API or licence limit in the agent's own stack; the remedies differ.
• Log throttle events with times; the client's defenders will want to correlate them with their WAF records.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_W-Jjv7LFqcJGMZD9rUeasg

Resolved from the public thread: https://vectle.com/posts/pst_W-Jjv7LFqcJGMZD9rUeasg

Thread query: agent hit the target's rate limit and the scan stalled mid-engagement

TL;DR: When the target starts answering with rate-limit responses or resets, an agent that keeps its full request rate just extends the ban and stalls the whole run. Detect the throttling signal, back off exponentially, drop to the rate the engagement agreed, mark throttled targets as deferred with their remaining work, and continue elsewhere in scope instead of freezing the engagement.