Agent Failure Archive MCP Server

Agent Failure Archive

186 post-mortems from running a multi-session AI agent system in production for 8 months. Pay per call with x402. No signup, no API key, no subscription.

Live: https://desktop-ai2ata5-1.tailfeb765.ts.net Try it free, right now: /sample

Public repositories show you code that worked. This is the other half: the wiring that looked correct, passed review, ran for weeks, and was dead the whole time.

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Why this exists

The expensive failures in agent systems are not the loud ones. A crash gets fixed in an hour. The costly ones are silent: a repair routine wired to a signal nobody consumes, a watcher that exits 0 after its session expired, a detector whose output is identical whether the system is healthy or broken.

Those failures are almost never written down, because writing them down requires having run the thing long enough to be bitten and having kept records. This archive is that record.

A real entry (case adr-136):

A broadcast call failed with an internal error. The caller saw the error. The five receiving sessions only ever checked for an acknowledgement, so they saw nothing and retried forever. Seven sessions writing heartbeats plus the retry storm collapsed the database into lock contention.

Root cause: the failure was visible to the sender and invisible to the receiver. Asymmetric error visibility, not the broadcast bug itself.

Of the 186 cases, 174 carry measured evidence (durations, counts, rates) and 155 name a root cause rather than just a symptom.

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The measurement half

For eight months this system was pointed at one question: can you measure how a single person's language departs from the general language, without collapsing that person into a score?

It mostly failed, and the failures were more interesting than the goal. 107 of the 186 cases are measurement failures: detectors that returned the same output whether the signal was present or absent, dose-response arms where the same parameter turned out to be two different treatments, positive controls that were never run, a corpus that was 2.3x smaller than the file count claimed, an instrument that kept measuring itself and reporting the reading as a finding.

Those are the cases behind /research. If you are building anything that claims to measure a person -- style, personality, authorship, fit to a profile -- this is the catalogue of ways that claim breaks before you notice it has broken.

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Endpoints

Payment: USDC on Base (eip155:8453), settled through a keyless facilitator. Any x402 client works, and a browser gets a wallet-connect paywall instead of raw JSON.

# free, no wallet needed
curl https://desktop-ai2ata5-1.tailfeb765.ts.net/sample

# paid, via any x402-capable client
curl https://desktop-ai2ata5-1.tailfeb765.ts.net/search?q=silent+failure+cron

/audit is the one to reach for before you write "we found that". Hand it your conclusion and what you actually measured, and it returns the checks your claim trips: a null result with no positive control, treatment arms that got the same parameter but not the same treatment, a denominator counting the same unit repeatedly, an exit-0 process that did nothing, a cached view read as if it were state. Nine checks, every one of them a failure that really shipped here, with the numbers measured at the time.

It is deterministic. No model is consulted, so the same input always returns the same audit, it answers in milliseconds, and when it is wrong you can see exactly why. A clean pass is not proof your claim is true; it means these nine known ways of fooling yourself were considered.

Paste a paragraph, not a tidy claim. Both /precheck and /audit accept text= instead of claim=. Give them a chunk of your findings and they pick out the sentences that assert something, then check each one separately:

curl -sG https://desktop-ai2ata5-1.tailfeb765.ts.net/precheck \
  --data-urlencode "text=We ran the new ranker on 40 sampled queries and found no significant
difference. The watcher is healthy: it exits 0 every run. Our corpus contains 4279 documents,
2x the previous release."

returns three claims, each held for a different reason: the null result has no positive control, the healthy watcher would look identical having done nothing, and the corpus count may be counting re-dumped snapshots. Sentence selection is deterministic too, driven by the same check table rather than by a model, so prose with no claims in it comes back empty instead of inventing findings.

/brief is the one to reach for before doing something irreversible: describe the action in plain words and it returns the ways that class of action has actually gone wrong, plus the prevention line each incident produced.

/contents is the shelf. Two sample cases cannot tell you whether the whole corpus is worth a dollar, so this returns all 186 titles, each tagged with which of the nine traps it illustrates, and nothing else. The distribution as of today: 108 cases involve reading a cached view as state, 83 involve a denominator counting the same unit twice, 71 involve something built with no caller, 36 involve a process that exited 0 having done nothing. Titles only, no bodies, no payment.

/archive exists because a corpus is worth more whole than sliced. One payment ends the transaction; there is nothing to cancel afterwards.

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Use it as an MCP server

mcp_server.py exposes the whole archive as tools for Claude Desktop, Cursor, or any MCP-compatible agent. The free tools need no wallet and no configuration.

pip install "mcp[cli]" requests            # free tools only
pip install "x402[mcp]" eth-account        # add this for the paid tools

{
  "mcpServers": {
    "agent-failure-archive": {
      "command": "python3",
      "args": ["/absolute/path/to/mcp_server.py"],
      "env": { "X402_PRIVATE_KEY": "0x..." }
    }
  }
}

X402_PRIVATE_KEY is your wallet. It stays on your machine and is used locally to sign payment authorizations. It is never transmitted anywhere, and this server never logs it. Drop the env block entirely if you only want the free tools.

Without a key the paid tools do not fail silently: they return the reason, the payment challenge, and a pointer to the free equivalent.

Tested against mcp 2.1.0 and the 1.x FastMCP layout: eight tools listed, precheck answered with no wallet, audit degraded with a stated reason.

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What is not in here

• No personal data. Any source document mentioning a person, a business relationship, or a monetary amount is excluded whole, not redacted line by line.
• No operator utterances. The corpus keeps the structure of each incident, never the voice.
• Wallet addresses, home paths, IP addresses, emails, API keys and session identifiers are masked before a document is ever considered for inclusion.

The filter is tested against a deliberately planted probe string on every build; if the detector fails to catch it, the build aborts. Current state: 0 leaks across 186 cases, positive control passing.

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Measured notes on the market

While trying to sell a dollar of this, we measured how x402 discovery and revenue actually behave, and several widely held assumptions turned out to be wrong. Written up with the exact unauthenticated calls so you can check rather than trust: MARKET.md.

Short version: the modal price is a tenth of a cent to three cents but a seller doing $0.85 per call at 125,000 calls a month exists; eight of the top ten buyers pay exactly one seller, so the headline volume is vertical integration rather than a marketplace; the directory chat everyone assumes will find your service has not been used since May; and getting into the facilitator directory needs one observed payment attempt, not a completed sale.

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Honest limits

• This is one operator's system. It is prior art, not a guarantee, and not a statistical sample of agent systems in general.
• Coverage is skewed toward what that system does a lot of: multi-session coordination, hook and cron wiring, retrieval pipelines, inter-process messaging, scheduled repair, and the measurement work described above.
• Some entries record a failure whose fix was later found to be wrong. Those are kept, with the correction, because the correction is usually the more useful half.
• Nothing here has sold yet. At the time of writing the receiving address has taken in exactly $0.00. That number is checked on-chain rather than from server logs, and this line gets updated when it changes.

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Running it yourself

pip install -r requirements.txt
X402_PAY_TO=0xYourAddress uvicorn server:app --port 8402

Without X402_PAY_TO the paid routes return 503 with the reason stated in the body, rather than failing quietly. That behaviour is not incidental. It is case adr-546 applied to this service's own code.