agentprobe.org
Smithery Registryauth-required: 247timeout: 3tls-fail: 1connect-fail: 1294% · 263models.devok: 79auth-required: 99protocol-mismatch: 2http-error: 11timeout: 2connect-fail: 2dns-fail: 2blocked: 489% · 201Docker MCP Catalogok: 14auth-required: 7protocol-mismatch: 4http-error: 2dns-fail: 370% · 30Official MCP Registryok: 16,863auth-required: 8,900protocol-mismatch: 4,451http-error: 556timeout: 494tls-fail: 255connect-fail: 6,406dns-fail: 619blocked: 367% · 38,547A2A Registry (a2aregistry.org)A2A Registry (a2aregis…ok: 317auth-required: 34card-invalid: 16protocol-mismatch: 188http-error: 10timeout: 73tls-fail: 1connect-fail: 3dns-fail: 3unprobeable: 354% · 648agent-tools.cloudok: 31,296auth-required: 23,964card-invalid: 1,241protocol-mismatch: 8,657http-error: 49,446timeout: 2,057tls-fail: 798connect-fail: 7,818dns-fail: 6,303blocked: 14unprobeable: 37142% · 131,965x402 Bazaar (Coinbase CDP discovery)x402 Bazaar (Coinbase…ok: 24,318auth-required: 200protocol-mismatch: 608http-error: 50,514timeout: 342connect-fail: 12dns-fail: 632% · 76,000Agenstryok: 12,176auth-required: 6,199card-invalid: 1,371protocol-mismatch: 22,960http-error: 6,068timeout: 1,493tls-fail: 372connect-fail: 4,687dns-fail: 1,327blocked: 110unprobeable: 29132% · 57,054Project NANDA Index (MIT)Project NANDA Index (M…ok: 5auth-required: 2card-invalid: 2http-error: 30timeout: 21connect-fail: 2dns-fail: 52blocked: 36% · 117Hugging Face Hub (Spaces/Models tagged MCP or agent)Hugging Face Hub (Spac…auth-required: 2protocol-mismatch: 2,494http-error: 8,428timeout: 42connect-fail: 1,418dns-fail: 110% · 12,395Smithery RegistrySmithery Regist…auth-required: 247timeout: 3tls-fail: 1connect-fail: 1294% · 263models.devok: 79auth-required: 99protocol-mismatch: 2http-error: 11timeout: 2connect-fail: 2dns-fail: 2blocked: 489% · 201Docker MCP CatalogDocker MCP Cata…ok: 14auth-required: 7protocol-mismatch: 4http-error: 2dns-fail: 370% · 30Official MCP RegistryOfficial MCP Re…ok: 16,863auth-required: 8,900protocol-mismatch: 4,451http-error: 556timeout: 494tls-fail: 255connect-fail: 6,406dns-fail: 619blocked: 367% · 38,547A2A Registry (a2aregistry.org)A2A Registry (a…ok: 317auth-required: 34card-invalid: 16protocol-mismatch: 188http-error: 10timeout: 73tls-fail: 1connect-fail: 3dns-fail: 3unprobeable: 354% · 648agent-tools.cloudagent-tools.clo…ok: 31,296auth-required: 23,964card-invalid: 1,241protocol-mismatch: 8,657http-error: 49,446timeout: 2,057tls-fail: 798connect-fail: 7,818dns-fail: 6,303blocked: 14unprobeable: 37142% · 131,965x402 Bazaar (Coinbase CDP discovery)x402 Bazaar (Co…ok: 24,318auth-required: 200protocol-mismatch: 608http-error: 50,514timeout: 342connect-fail: 12dns-fail: 632% · 76,000Agenstryok: 12,176auth-required: 6,199card-invalid: 1,371protocol-mismatch: 22,960http-error: 6,068timeout: 1,493tls-fail: 372connect-fail: 4,687dns-fail: 1,327blocked: 110unprobeable: 29132% · 57,054Project NANDA Index (MIT)Project NANDA I…ok: 5auth-required: 2card-invalid: 2http-error: 30timeout: 21connect-fail: 2dns-fail: 52blocked: 36% · 117Hugging Face Hub (Spaces/Models tagged MCP or agent)Hugging Face Hu…auth-required: 2protocol-mismatch: 2,494http-error: 8,428timeout: 42connect-fail: 1,418dns-fail: 110% · 12,395
sources ranked by alive share (≥ 20 probed endpoints), each row normalised to 100% · right: alive share · probed · click a segment for the endpoints
37 sources
317,230 probed endpoints attributed
Common Crawl llms.txt corpus (CC-MAIN-2026-30)Common Crawl llms.txt…14,362 of 597,970 listingsAgenstry57,098 of 301,330 listingsx402 Bazaar (Coinbase CDP discovery)x402 Bazaar (Coinbase…114,000 of 145,809 listingsagent-tools.cloud132,246 of 120,439 listingsOfficial MCP Registry38,588 of 57,719 listingsHugging Face Hub (Spaces/Models tagged MCP or agent)Hugging Face Hub (Spac…12,395 of 13,292 listingsA2A Registry (a2aregistry.org)A2A Registry (a2aregis…648 of 816 listingsProject NANDA Index (MIT)Project NANDA Index (M…229 of 340 listingsSmithery Registry263 of 319 listingsDocker MCP Catalog30 of 270 listingsmodels.dev201 of 240 listingsGlobal Chat agent directoryGlobal Chat agent dire…25 of 25 listingsagentprobe.org (self)5 of 4 listingsCommon Crawl llms.txt corpus (CC-MAIN-2026-30)Common Crawl ll…Common Crawl llms.txt corpus (CC-MAIN-2026-30): 14,362 of 597,970 listings14,362AgenstryAgenstry: 57,098 of 301,330 listings57,098x402 Bazaar (Coinbase CDP discovery)x402 Bazaar (Co…x402 Bazaar (Coinbase CDP discovery): 114,000 of 145,809 listings114,000agent-tools.cloudagent-tools.clo…agent-tools.cloud: 132,246 of 120,439 listings132,246Official MCP RegistryOfficial MCP Re…Official MCP Registry: 38,588 of 57,719 listings38,588Hugging Face Hub (Spaces/Models tagged MCP or agent)Hugging Face Hu…Hugging Face Hub (Spaces/Models tagged MCP or agent): 12,395 of 13,292 listings12,395A2A Registry (a2aregistry.org)A2A Registry (a…A2A Registry (a2aregistry.org): 648 of 816 listings648Project NANDA Index (MIT)Project NANDA I…Project NANDA Index (MIT): 229 of 340 listings229Smithery RegistrySmithery Regist…Smithery Registry: 263 of 319 listings263Docker MCP CatalogDocker MCP Cata…Docker MCP Catalog: 30 of 270 listings30models.devmodels.dev: 201 of 240 listings201Global Chat agent directoryGlobal Chat age…Global Chat agent directory: 25 of 25 listings25agentprobe.org (self)agentprobe.org…agentprobe.org (self): 5 of 4 listings5
remote endpoints each source contributes (listings without a remote URL are unprobeable by definition)

Ranking

sourceprobedaliveconformantlistingsremote endpoints
1Smithery Registry26393.9%0.0%319263
2models.dev20188.6%39.3%240201
3Docker MCP Catalog3070.0%46.7%27030
4Official MCP Registry38,54766.8%43.7%57,71938,588
5A2A Registry (a2aregistry.org)64854.2%48.9%816648
6agent-tools.cloud131,97041.9%23.7%120,439132,246
7x402 Bazaar (Coinbase CDP discovery)76,00032.3%32.0%145,809114,000
8Agenstry57,05532.2%21.3%301,33057,098
9Project NANDA Index (MIT)1176.0%4.3%340229
10Hugging Face Hub (Spaces/Models tagged MCP or agent)12,3950.0%0.0%13,29212,395
—agentprobe.org (self)4too few probed to rank45

Sources

Every registry, directory and convention we harvest — including the ones with no machine-readable access, because that is a finding too.

sourceoperatorkindprotocolsaccessclaimedlast harvestsnotes
Common Crawl llms.txt corpus (CC-MAIN-2026-30)
commoncrawl-llms-txt
Common Crawl Foundation datasetllms-txt parquet verified
https://huggingface.co/datasets/commoncrawl/llms.txt/resolve/main
584,107 2026-11-05T22:18 running 0 rec / 0 ep
2026-11-05T08:41 ok 598225 rec / 14410 ep
2026-11-05T02:36 ok 598225 rec / 14410 ep
Common Crawl terms of use; dataset is public on Hugging Face. Companion to the CC llms.txt report (584,107 files from the July 2026 crawl; two thirds plugin-generated, half spec-conformant). We add: are they still there, do they still parse, and do these hosts also publish agent cards / ard.json / agents.txt.
GitHub repositories tagged mcp-server
github-topic-mcp-server
GitHub datasetmcp api verified
https://api.github.com/search/repositories?q=topic:mcp-server&per_page
27,813 2026-11-06T02:25 partial 1000 rec / 0 ep
2026-11-05T20:29 partial 800 rec / 0 ep
2026-11-05T14:21 partial 900 rec / 0 ep
GitHub ToS; search API 10 req/min unauthenticated, 30/min with token. Baseline for 'how many MCP servers exist in code' vs how many are hosted.
npm packages with keyword mcp / mcp-server
npm-keyword-mcp
npm, Inc. (GitHub) datasetmcp api verified
https://registry.npmjs.org/-/v1/search?text=keywords:mcp-server&size=2
8,228 2026-11-06T02:26 ok 8000 rec / 0 ep
2026-11-05T20:30 ok 8750 rec / 0 ep
2026-11-05T14:22 ok 9243 rec / 0 ep
npm public registry API; bulk use allowed with reasonable rate. Search API pagination caps around 10,000 results; slice by additional text terms if needed.
AI Agents Directory (aiagentsdirectory.com)
aiagentsdirectory
aiagentsdirectory.com directoryother html-scrape verified
https://aiagentsdirectory.com/sitemap.xml
5,982 Website ToS; no API. Human-facing catalogue; use only for vendor-domain harvesting to feed the well-known crawl.
AI Agents List (aiagentslist.com)
aiagentslist
aiagentslist.com directoryother mcp html-scrape verified
https://aiagentslist.com/api/sitemap-agents.xml
1,245 Website ToS; no API. Negative result for the market analysis: human-facing catalogue, zero probe-able endpoints.
Agenstry
agenstry
Agenstry (independent, NL) directorya2a mcp openapi other json-file verified
https://agenstry.com/api/feed/all.jsonl.gz
182,671 2026-11-06T02:37 ok 298883 rec / 58218 ep
2026-11-05T20:46 ok 298473 rec / 58164 ep
2026-11-05T14:56 running 0 rec / 0 ep
Federation feed CC-BY-4.0 with attribution (per /docs/api); robots.txt opts IN to AI crawling/training. In-session feed: 182,671 rows = mcp 158,022, skill 18,124, paid_api 4,160, a2a_agent 2,243, workflow 95, a2a 27. Site claims 6,430 A2A agents + 158,022 MCP servers across 8 registries. Direct competitor to agentprobe (probes, conformance-scores, drift feeds /feed/drift.jsonl).
Cline MCP Marketplace
cline-mcp-marketplace
Cline Bot Inc. directorymcp api verified
https://api.cline.bot/v1/mcp/marketplace
199 2026-11-06T02:25 ok 199 rec / 0 ep
2026-11-05T20:29 ok 199 rec / 0 ep
2026-11-05T14:21 ok 199 rec / 0 ep
Public endpoint, no stated terms.
Glama MCP directory
glama-mcp
Glama (glama.ai) directorymcp api unverified
https://glama.ai/api/mcp/v1/servers?first=100
83,047 2026-11-06T02:24 skipped 0 rec / 0 ep
2026-11-05T20:29 skipped 0 rec / 0 ep
2026-11-05T14:20 skipped 0 rec / 0 ep
API key required (401 without). API Data License: visible attribution to Glama on every page that displays the data and a link to each record's Glama listing (`url` field); commercial exemptions on request. https://glama.ai/policies/terms-of-service Unauthenticated GET returned HTTP 401 in-session (auth requirement confirmed, shape not). Listing page states 83,047 servers, 35,383 "remote-capable". Bearer token in Authorization header.
Global Chat agent directory
global-chat-directory
Global Chat (global-chat.io) directorya2a agents-txt other api verified
https://global-chat.io/api/agents
25 2026-11-06T02:37 ok 25 rec / 25 ep
2026-11-05T20:46 ok 25 rec / 25 ep
2026-11-05T14:56 ok 25 rec / 25 ep
No stated API terms; robots.txt explicitly allows AI crawlers. Tiny curated list of ecosystems, not agents. Low value for endpoint harvest.
Moltbook (social network for AI agents)
moltbook
Moltbook directoryother stats-only verified
https://www.moltbook.com/api/v1/stats
2,911,186 2026-09-09T20:20 failed 0 rec / 0 ep
2026-09-09T14:09 failed 0 rec / 0 ep
2026-09-09T08:01 failed 0 rec / 0 ep
Bearer API key for write; read endpoints above respond anonymously; no bulk export. The API exposes aggregate counts only (/api/v1/stats); there is no listing or bulk export, so nothing to harvest.
PulseMCP
pulsemcp
PulseMCP directorymcp api unverified
https://api.pulsemcp.com/v0.1/servers?limit=100
21,961 2026-11-06T02:24 skipped 0 rec / 0 ep
2026-11-05T20:29 skipped 0 rec / 0 ep
2026-11-05T14:20 skipped 0 rec / 0 ep
API key required; docs at https://www.pulsemcp.com/api/docs/v0.1. Aggregates upstream registry data (read-only sub-registry). v0beta (/v0beta/servers) is being sunset — returned HTTP 410 API_SUNSET in-session (100% failure from Sept 2026). /v0.1/servers returned 401 "Invalid or missing API key" (header X-API-Key) — endpoint exists, key needed. Directory page shows 21,961 servers.
agent-tools.cloud
agent-tools-cloud
agent-tools.cloud (independent) directorymcp a2a openapi other api verified
https://agent-tools.cloud/api/v1/export?limit=1000
22,755 2026-11-06T02:28 ok 89158 rec / 137011 ep
2026-11-05T20:33 ok 89158 rec / 137011 ep
2026-11-05T14:39 ok 88449 rec / 133767 ep
robots.txt: 'Crawlers and AI agents are welcome to index and use the public catalogue and JSON API.' Aggregator (sources[] names upstream e.g. paygent-discover, x402 bazaar) — dedupe against x402-bazaar. Harvested via /api/v1/export (keyset, kind=x402|mcp|a2a, limit 1000); /search caps offset at 1000. Records carry sources[] = upstream registries the entry was mirrored from.
mcp.so
mcp-so
mcp.so (idoubi / ChatMCP) directorymcp html-scrape verified
https://mcp.so/sitemap.xml?section=servers&page=1
18,643 No published API terms; standard website scraping — respect robots.txt and rate. Sitemap also has section=agents (23) and section=clients. 18x1000 + 643 server URLs.
x402 Bazaar (Coinbase CDP discovery)
x402-bazaar
Coinbase Developer Platform directoryopenapi other api verified
https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources?limi
15,578 2026-11-05T22:12 suspect 36305 rec / 0 ep
2026-11-05T08:38 ok 115788 rec / 114540 ep
2026-11-05T02:33 ok 114928 rec / 113684 ep
Public, no CDP key needed ('Bazaar discovery is public'); CDP ToS. Largest source of probe-able x402 HTTP endpoints; agent-tools.cloud re-indexes it.
OpenRouter models API
openrouter-models
OpenRouter, Inc. model-apillm-api api verified
https://openrouter.ai/api/v1/models
430 2026-11-06T02:41 ok 454 rec / 0 ep
2026-11-05T21:32 ok 454 rec / 0 ep
2026-11-05T08:08 ok 455 rec / 0 ep
Public GET, no key; OpenRouter ToS.
models.dev
models-dev
Anomaly (SST / OpenCode) model-apillm-api json-file verified
https://models.dev/api.json
7,560 2026-11-06T02:41 ok 235 rec / 205 ep
2026-11-05T21:32 ok 235 rec / 205 ep
2026-11-05T08:08 ok 235 rec / 205 ep
Open data, MIT (github.com/sst/models.dev). In-session: 213 providers, 7,560 models. Provider base URLs (213) are the probe targets.
Agent0 ERC-8004 subgraphs (The Graph)
erc-8004-agent0-subgraph
Agent0 Lab (github.com/agent0lab/subgraph), hosted on The Graph Network onchainerc8004 api unverified
https://gateway.thegraph.com/api/<API_KEY>/subgraphs/id/43s9hQRurMGjuY
39,000 2026-11-06T02:41 skipped 0 rec / 0 ep
2026-11-05T21:32 skipped 0 rec / 0 ep
2026-11-05T08:08 skipped 0 rec / 0 ep
Free Subgraph Studio API key required (100k queries/month free tier); MIT subgraph code. Cheapest way to bulk-list ERC-8004 agents with already-parsed endpoints. Not fetched in-session (needs key).
ERC-8004 Trustless Agents — Identity Registry (on-chain)
erc-8004-identity-registry
Ethereum community (EIP-8004 authors; contracts by the 8004 team) onchainerc8004 a2a mcp rpc unverified
https://mainnet.base.org
39,000 Public chain data; RPC provider ToS (public endpoints rate-limited). In-session eth_call totalSupply() reverted on both Ethereum and Base (registry is not ERC721Enumerable) — count via events or an indexer. ~39k registrations across 15 chains in the first 90 days (Quicknode, Apr 2026); "40K+ agents on Base in two weeks" (press). Indexers: agent0 subgraphs (see next entry); Quicknode explorer https://erc-8004.quicknode.com (REST /v1/agents, x402-paid $0.001 USDC/req, 60 req/min); agentscan.info (web UI, no public API found).
Virtuals Protocol agents
virtuals-protocol
Virtuals Protocol onchainother api verified
https://api.virtuals.io/api/virtuals?pagination[page]=1&pagination[pag
83,112 2026-11-06T02:46 running 0 rec / 0 ep
2026-11-05T21:37 ok 86350 rec / 0 ep
2026-11-05T08:12 ok 86349 rec / 0 ep
Undocumented public API; Virtuals ToS. 83,112 records in-session (filters[status]=AVAILABLE narrows to launched tokens).
A2A Registry (a2aregistry.org)
a2a-registry-org
Prassanna Ravishankar / community (github.com/prassanna-ravishankar/a2a-registry) registrya2a api verified
https://a2aregistry.org/api/agents?limit=50&offset=0
376 2026-11-06T02:28 ok 647 rec / 647 ep
2026-11-05T20:33 ok 642 rec / 642 ep
2026-11-05T14:38 ok 642 rec / 642 ep
MIT-licensed project; read API needs no key. /api/stats for totals. Older docs mention a static registry.json — it no longer exists (www.a2aregistry.org/registry.json serves the SPA, raw GitHub path 404). Also exposes an MCP server at https://a2aregistry.org/mcp/. Stats in-session: 376 agents, 363 healthy.
AGNTCY Agent Directory Service (Outshift hosted)
agntcy-agent-directory
AGNTCY (Linux Foundation) / Cisco Outshift registrya2a mcp other rpc unverified
https://ads.outshift.io/
Apache-2.0 software; hosted instance requires an Outshift account (OIDC). In-session: dir.agntcy.org is docs only; https://ads.outshift.io/ returns HTTP 401 JSON; prod.api.ads.outshift.io demands a client TLS certificate; agent-directory.outshift.com does not resolve. Treat as NOT publicly harvestable without registration.
Agentverse (Fetch.ai Almanac)
agentverse-fetch-ai
Fetch.ai registryother api verified
https://agentverse.ai/v1/search/agents
10,000 2026-11-06T02:41 ok 10000 rec / 0 ep
2026-11-05T21:32 ok 10000 rec / 0 ep
2026-11-05T08:08 ok 10000 rec / 0 ep
Undocumented public search used by the web UI; Fetch.ai ToS. `total` is capped at 10,000 in the search index; real Almanac count is larger (Fetch.ai claims 1M+ registrations).
Cloudflare signature-agent registry (Web Bot Auth) + Radar bots directory
cloudflare-web-bot-auth-registry
Cloudflare registryother json-file unverified
https://assets.radar.cloudflare.com/bots/signature-agent-registry.txt
2026-11-05T22:18 skipped 0 rec / 0 ep
2026-11-05T08:41 skipped 0 rec / 0 ep
2026-11-05T02:36 skipped 0 rec / 0 ep
Registry file published for operators to import (blog.cloudflare.com/agent-registry/); Radar API under Cloudflare API ToS with free token. The static registry file answers 403 to every client; needs a (free) Cloudflare API token, and with it the Radar API path instead of the asset URL.
Docker MCP Catalog
docker-mcp-catalog
Docker, Inc. registrymcp json-file verified
https://desktop.docker.com/mcp/catalog/v2/catalog.yaml
267 2026-11-06T02:25 ok 270 rec / 30 ep
2026-11-05T20:29 ok 270 rec / 30 ep
2026-11-05T14:21 ok 270 rec / 30 ep
Public catalog file; Apache-2.0 repo (docker/mcp-registry). Counted in-session: 234 server, 30 remote, 3 poci.
Hugging Face Hub (Spaces/Models tagged MCP or agent)
huggingface-hub-mcp
Hugging Face registrymcp llm-api api verified
https://huggingface.co/api/spaces?filter=mcp-server&limit=1000
10,192 2026-11-06T02:41 ok 12391 rec / 12391 ep
2026-11-05T21:29 ok 12378 rec / 12378 ep
2026-11-05T08:08 ok 12337 rec / 12337 ep
Public Hub API; HF ToS. Anonymous OK; token raises limits. Second-largest source of live MCP HTTP endpoints after the official registry; sleeping Spaces return 5xx until woken.
Microsoft Entra Agent ID / Agent 365 registry
microsoft-entra-agent-registry
Microsoft registrya2a mcp other none unverified Not public. Microsoft Graph API terms; requires Entra tenant + admin consent. Negative result: no harvestable public surface.
Official MCP Registry
mcp-registry-official
Model Context Protocol project (Linux Foundation / Agentic AI Foundation) registrymcp api verified
https://registry.modelcontextprotocol.io/v0/servers?limit=100&version=
28,110 2026-11-06T02:19 ok 56493 rec / 38693 ep
2026-11-05T20:17 ok 56377 rec / 38604 ep
2026-11-05T14:08 ok 56205 rec / 38465 ep
Public API, no stated bulk restriction. Server data is publisher-submitted; be polite. Counted in-session with version=latest: 28,110 servers, 16,097 with remotes (15,526 streamable-http + 1,070 sse remote entries), 13,046 with packages. Largest single open source of probe-able MCP URLs.
Project NANDA Index (MIT)
nanda-index
Project NANDA, MIT Media Lab (github.com/projnanda) registrya2a mcp other api verified
https://index.projectnanda.org/api/agents?limit=100&page=1
400 2026-11-06T02:28 ok 300 rec / 469 ep
2026-11-05T20:33 ok 300 rec / 469 ep
2026-11-05T14:39 ok 300 rec / 469 ep
Undocumented public JSON used by the SPA (api.projectnanda.org does not resolve); no stated terms. Many entries are hackathon/test agents; `status` and `lastSeen` fields help triage. Verified 2026-09-07: pagination is broken server-side — pages 1-3 return 350 distinct records, every page >= 4 returns the same 50 rows while `total` claims 13,606 and hasNext stays true until page 69. Harvest stops on repeated page; effective public listing ≈ 400.
Smithery Registry
smithery
Smithery AI registrymcp api verified
https://registry.smithery.ai/servers?pageSize=100&page=1
11,779 2026-11-06T02:24 ok 500 rec / 497 ep
2026-11-05T20:29 ok 500 rec / 497 ep
2026-11-05T14:20 ok 500 rec / 497 ep
Public read without key in-session; Smithery ToS apply. API key (Bearer) documented for higher limits. IMPORTANT: anonymous listing is capped at 500 rows per query (totalPages=5 at pageSize=100, page 6 returns []), although totalCount=11,779. To harvest all, slice with q= filters (q=is:deployed -> 8,536; also is:verified, owner:, category, free-text) or obtain an API key.
A2A Agent Card well-known path
wellknown-a2a-agent-card
A2A Project (Linux Foundation) wellknown-conventiona2a wellknown-fetch verified
https://{domain}/.well-known/agent-card.json
Apache-2.0 spec. Sample record fetched in-session from global-chat.io. Domain seed lists: all registries above + agents.txt A2A: lines.
Agentic Resource Discovery (ARD) catalog well-known path
wellknown-ard-catalog
ARD project (Google-led; Microsoft, GitHub, Hugging Face, Cisco, Salesforce et al.) wellknown-conventionard mcp a2a openapi wellknown-fetch verified
https://{domain}/.well-known/ard.json
Apache-2.0 spec. agent-tools.cloud/.well-known/ai-catalog.json returned 404 in-session — adoption still thin; find registries via entries typed application/ai-registry+json.
MCP server card well-known path (SEP-2127 / SEP-1960 / IETF draft)
wellknown-mcp-server-card
Model Context Protocol project wellknown-conventionmcp wellknown-fetch verified
https://{domain}/.well-known/mcp/server-cards.json
MIT spec repo. Treat any hit as signal; expect very low hit rate until a SEP merges.
NANDA AgentFacts well-known path
wellknown-nanda-agent-facts
Project NANDA (MIT) wellknown-conventionother a2a mcp wellknown-fetch unverified
https://{domain}/.well-known/agent-facts.json
Open spec (MIT project); unverified. Low adoption outside the NANDA index; include for completeness.
Web Bot Auth key directory (signature-agent card)
wellknown-http-message-signatures-directory
IETF drafts (Cloudflare authors) wellknown-conventionother wellknown-fetch unverified
https://{domain}/.well-known/http-message-signatures-directory
IETF draft; each operator's own terms. Not fetched in-session.
agentprobe.org (self)
agentprobe-self
Venture Inventory GmbH wellknown-conventiona2a ard llms-txt json-file unverified
https://agentprobe.org/.well-known/ard.json
3 2026-11-05T08:45 ok 4 rec / 5 ep
2026-11-05T02:40 ok 4 rec / 5 ep
2026-11-04T20:45 ok 4 rec / 5 ep
ours Dogfood entry. If this row is not 'ok' the site is misconfigured.
agents.txt / agents.json
wellknown-agents-txt
agents-txt project (github.com/agents-txt/agents-txt) wellknown-conventionagents-txt mcp a2a wellknown-fetch verified
https://{domain}/agents.txt
CC0 1.0 spec text. Also try /.well-known/agents (JSON) mentioned in the kaylacar variant; IANA registration pending.
llms.txt
wellknown-llms-txt
Answer.AI (Jeremy Howard) / community wellknown-conventionllms-txt wellknown-fetch verified
https://{domain}/llms.txt
CC-BY spec; site content under each site's own terms. Adoption proxy, not an endpoint source. directory.llmstxt.cloud lists adopters (HTML).