Show HN: agent-usage-guard – a Claude Code mod to protect your usage window

A developer released agent-usage-guard, a Claude Code mod that reads a plan's live 5-hour and weekly usage percentages and blocks runaway agent spend before it happens, requiring Claude Code v2.1.287 or later. The mod caps concurrent agents at 4, agent starts or resumes at 12 per 10 minutes, and subagent tokens at 10M per 10 minutes across every session on a machine, refusing new agents once a plan window reaches 95% and asking for approval at 80%. The author cites a session that spawned 394 subagent calls, 341 running at once, and pushed 84M context tokens in ten minutes, plus 12 lockouts across 60 days of personal logs, as the failure mode the guard targets.

Stops Claude Code from spending your five-hour usage window in ten minutes. agent-usage-guard is a Claude Code mod https://code.claude.com/docs/en/plugins/mods/overview : it runs inside Claude Code and holds runaway spend before it happens. It reads your plan's live usage, and it holds subagent fan-out, heavy-context churn and retry loops. <sub Recorded from Claude Code's interactive UI with the guard loaded. A scripted local API https://github.com/rbartoli/agent-usage-guard/blob/main/demo/scripted-api.ts stands in for Claude, so the sessions and token counts are staged and no usage is spent. Every question on screen is the guard's own. Rebuild it https://github.com/rbartoli/agent-usage-guard/blob/main/demo/render.sh from the Northstar fixture https://github.com/rbartoli/agent-usage-guard/blob/main/demo/fixture/northstar-api .</sub It acts before the spend, not after it: before an agent starts, a prompt is sent, or a tool call runs. Agent limits hold across every Claude Code session on your machine, and fan-out and heavy context are capped at any usage level, not only near the limit. When you are at the keyboard it asks you, in Claude Code's own question dialog. When nobody can answer, it refuses and tells Claude why, so the model can wait, batch the work, or stop. /agent-guard report shows what it did. - Plan-aware. It reads the 5-hour and weekly percentages Claude Code reports, and keeps the end of the window for you. - One answer covers a while. An approval lifts its condition until it clears or times out, so the same question does not come back call after call. - Local and privacy-minimal. No network, no processes. It stores counts and coarse buckets, never prompt text, tool inputs or model output. - Fails open. If one of its hooks fails, the event goes ahead: a broken guard never breaks your session. The one exception is an agent it could not judge in time, which is refused so that Claude starts it again. Run these commands inside Claude Code v2.1.287 or later: /plugin marketplace add rbartoli/agent-usage-guard /plugin install agent-usage-guard@agent-usage-guard /reload-plugins Then run /agent-guard to see what it sees. Mods are on by default; the overview https://code.claude.com/docs/en/plugins/mods/overview turn-mods-on-or-off lists the settings that turn them off. One afternoon I gave Claude Code a research prompt at max effort. It spawned 394 subagent calls, 341 of them running at once, and pushed 84M context tokens through the API in ten minutes. Session over: "Claude usage limit reached." Locked out until the window reset. That wasn't a one-off. Sixty days of my own logs held 12 lockouts and 166 ten-minute windows with agent bursts. The failure mode multiplies: a large context × rapid tool loops × parallel agents × blind retries . Each protection below removes one factor. And it's not just me: 339 subagents from a single prompt https://www.reddit.com/r/ClaudeAI/comments/1u5d02w/ , half a weekly Max plan consumed by recursive spawning https://github.com/anthropics/claude-code/issues/68619 , and multi-agent runs using ~15× the tokens of a chat session https://www.anthropic.com/engineering/built-multi-agent-research-system . | Area | Rule | Default | What happens | |---|---|---|---| | Plan windows | New agents need approval once a window is this full | 80% | asks; approval lasts until that window resets | | | New agents are refused once a window is this full | 95% | refuses | | | New agents need approval when the 5-hour window rises this fast | 20 points / 10 min | asks | | Agents | Agents running at once, across every session on this machine | 4 | asks | | | Agents started or resumed per 10 minutes, across this machine | 12 | asks | | | Tokens processed by subagents per 10 minutes, across this machine | 10M | asks | | | Subagents may not start their own agents | depth 1 | refuses | | Context | Claude is told once to keep the turn bounded | 300k tokens | adds a note to the prompt | | | A prompt that would re-read this much context | 500k tokens | asks: compact then send, send anyway, or cancel | | | Tool calls per 10 minutes while a conversation or agent carries this much | 20 calls at 400k | asks: keep going, compact after this turn, or stop | | | A heavy session idle long enough for its prompt cache to expire | 150k tokens, 1 h idle | asks before re-writing the cache | | Loops | The same tool call failing again and again, with no other call in between | 3 identical failures | refuses the identical retry | | | Refused agent calls within 10 minutes | 5 | pauses agent spawns for 10 min | Agents covers subagents, agent-team teammates, workflow agents, and finished subagents resumed with SendMessage . Each tool call is judged on the context of the loop that makes it, so a small subagent never inherits the main conversation's size. When it asks. The question appears in Claude Code's own dialog, the one Claude uses to ask you something, and the call waits for your answer. Agents started in parallel while it is open are held back, and Claude starts them again once you answer. If you allow it, that condition stays allowed for a while: a plan window until it resets, a heavy context until it shrinks for tool calls, an hour at most , the agent counts for 10 minutes. If you decline or dismiss the question, Claude is told not to start agents for the next 10 minutes AGENT GUARD WINDOW SECONDS , and is not asked again in that time. Typed words reach Claude, so you can answer "use haiku agents instead". When nobody can answer. In claude -p , the Agent SDK and dontAsk mode, an agent or tool gate refuses instead of asking. A heavy prompt is held with the reason, and so is a dormant heavy resume once the machine-wide cap of one per 10 minutes is reached. Claude reads each refusal as the tool's result. Repeat refusals of the same condition are worded differently each time and escalate: the second says nothing has changed and to try something else, the third says to end the turn. If a Stop hook such as /goal keeps reopening the turn, the refusal says the user has to decide. What it leaves alone. It never holds a background task's notification or another session's message, because that would lose the result. It no longer blocks prompts after a usage limit: since v2.1.234, Claude Code waits at a limit and continues at reset on its own autoContinueAtUsageLimit . The guard's job is to keep you from reaching the limit, and its journal counts the lockouts it did not prevent. /agent-guard status what the guard sees right now /agent-guard allow agents|context minutes lift its limits for this session default: all, 10 min /agent-guard pause minutes the same as allow, for every limit /agent-guard resume end an allow early, lift the agent pause, and let declined questions ask again /agent-guard report days what it did on this machine default: 7 days /agent-guard help these commands /agent-guard runs at once, even mid-turn, and never starts a model turn, so Claude never sees an override and cannot take one as permission. Sending allow-usage-guard or allow-agent-burst alone as a prompt, the markers of earlier versions, does the same as /agent-guard allow or allow agents . Checked against Claude Code v2.1.295: | Path | Coverage | |---|---| | Subagents, teammates and workflow agents | Held before they start agent.spawn | | A finished subagent sent new work with SendMessage | Held before it resumes, and counted as a start | | /subtask forks, and anything else that starts without agent.spawn | Counted when they start, never held: Claude Code offers no event before they do. Forks Claude starts through the Agent tool are held like any agent | | Claude Code's internal agents prompt suggestions, compaction | Not counted | | Plan-window percentages | From the last API response on a subscription, in claude -p too. API-key sessions report none, so only the token and count budgets apply | | Teammates running in their own terminal panes | Not visible: their loops run in other processes | | Sessions on other machines | Not counted: the cross-session records live in this machine's mod store | | Tools the API runs itself, such as the advisor | Not holdable: no tool event fires for them | Mods run in claude in a terminal, in the Desktop app's Code tab, in claude -p and the Agent SDK. They don't run in a Desktop-app WSL session where mods run https://code.claude.com/docs/en/plugins/mods/overview where-mods-run . Native limits still matter. Claude Code caps a session at 20 concurrent subagents CLAUDE CODE MAX CONCURRENT SUBAGENTS and three layers of nesting CLAUDE CODE MAX SUBAGENT SPAWN DEPTH . It has no limit on the total number of agents a session starts. The guard's defaults are stricter and span sessions; the native caps remain the outer wall for the paths the guard only counts. /agent-guard report 30 The report counts usage-limit lockouts each locked window once , plan-window threshold crossings, and every question and refusal by rule, with what you answered. It reads every session's journal on this machine and never leaves it. Set AGENT GUARD JOURNAL=0 to stop recording. A mod runs inside Claude Code with your permissions; read what a mod can reach https://code.claude.com/docs/en/plugins/mods/overview what-a-mod-can-reach before you install one. This one is about 2,400 lines of TypeScript with no dependencies, and claude plugin validate . lists every API it calls and every environment variable it reads: - It makes no network requests and starts no processes. - It decides only what the rules above describe: whether an agent starts, a prompt is sent, or a tool call runs. It asks you whenever you can answer, and gives the reason when it refuses. It reads permission modes but never changes them, and it writes no settings. - The only prompt it submits is your own: after "Compact, then send", it sends the prompt you typed, unchanged, once compaction finishes. - Its prompt hook passes your prompt on unchanged, adds a one-time note for Claude when the context passes 300k, or holds the prompt to ask you first when nobody can answer, it says why instead . Its SessionStart hook changes nothing. - It keeps its state in the mod store, a JSON file under ~/.claude/plugins/store/ . Each session writes its own counts running agents, recent starts and dormant resumes, subagent tokens per minute, its latest 5-hour reading , when it was last active kept 30 days, so a resumed session knows how long it sat idle , and its journal rows time, a session-id prefix, rule, tool name, context bucket such as 400-500k , plan window and percentage, refusal number, and your answer . - It never stores prompt text, tool inputs, error text or model output. A tool call is reduced to a 13-character fingerprint. Agent names stay in memory and are never written. - Journal days older than 90 days are deleted AGENT GUARD JOURNAL DAYS . - demo/ , which builds the GIF above, is not part of what runs. It starts Claude Code in a temporary home directory with a made-up API key for a scripted local API, and reads none of your credentials. Set AGENT GUARD=0 to turn it off without uninstalling it. Set these as environment variables, or under env in ~/.claude/settings.json . Times are in seconds; a value that isn't a number in range keeps its default, and /agent-guard says so. | Variable | Meaning default | |---|---| | AGENT GUARD | 0 , false , off or no turns the guard off 1 | | AGENT GUARD JOURNAL | 0 stops the journal 1 | | AGENT GUARD JOURNAL DAYS | Days of journal kept 90 | | AGENT GUARD WINDOW SECONDS | Rolling window for budgets, burn and refusals 600 | | AGENT GUARD AGENT MAX | Agents running at once on this machine 4 | | AGENT GUARD ROLLING MAX | Agent starts and resumes per window on this machine 12 | | AGENT GUARD AGENT TOKENS MAX | Subagent tokens per window on this machine 10000000 | | AGENT GUARD DEPTH MAX | Agent layers below the main conversation 1 | | AGENT GUARD LIMIT ASK PERCENT | Plan-window percentage from which new agents ask 80 | | AGENT GUARD LIMIT DENY PERCENT | Plan-window percentage from which new agents are refused 95 | | AGENT GUARD BURN PERCENT | 5-hour-window points per window that make new agents ask 20 | | AGENT GUARD CONTEXT WARN | Context at which Claude is told once to keep the turn bounded 300000 | | AGENT GUARD CONTEXT HARD | Context at which a prompt asks before it is sent 500000 | | AGENT GUARD TOOL CONTEXT | Context above which tool calls count against the tool budget 400000 | | AGENT GUARD TOOL MAX | Tool calls per window above that context 20 | | AGENT GUARD DORMANT SECONDS | Idle time after which a heavy session's cache counts as expired 3600 | | AGENT GUARD DORMANT CONTEXT | Context at which an idle session counts as heavy 150000 | | AGENT GUARD DORMANT MAX | Heavy dormant resumes per window on this machine when nobody can be asked 1 | | AGENT GUARD TOOL FAILURE MAX | Identical failures before the identical retry is refused 3 | | AGENT GUARD FUSE MAX | Refused agent calls per fuse period that pause spawns 5 | | AGENT GUARD FUSE SECONDS | The fuse period, and how long the pause lasts 600 | | AGENT GUARD PEER TTL SECONDS | How long another session's counts, or an agent with no sign of activity, still count 900 | The dormant default assumes the one-hour prompt cache that subscriptions get within plan usage. With an API key or extra usage, the cache lasts five minutes, so set AGENT GUARD DORMANT SECONDS=300 . The rules live in a harness-agnostic core core/ that performs no I/O. The Claude Code mod is its first adapter. docs/architecture.md https://github.com/rbartoli/agent-usage-guard/blob/main/docs/architecture.md describes the contract an adapter keeps and what another agent harness must offer to carry each rule. claude plugin validate . --strict claude plugin test claude plugin test runs the suite inside Claude Code's own test kit: unit tests of the core, and tests that fire real Claude Code events through the hooks module with no session, model or network. TESTING.md https://github.com/rbartoli/agent-usage-guard/blob/main/TESTING.md covers the layers and what each test proves. MIT