agenticweb.wiki

agents.txt

Discover Moved from the Read step to Discover. agents.txt is not one specification but a name shared by at least four non-converging proposals for a site-root text file that declares which agent-facing protocols (payments, auth, MCP endpoints, Skills, A2A) a site supports and where to find them [1][2][3][4]. It is filed here under "Discover" (what is here, and where?) rather than "Read", since every version found declares protocol/capability presence and location, not page content, and one variant (agents-txt.com) explicitly frames itself as complementary to A2A's AgentCard discovery and RFC 9727's API Catalog [1].

Overview

What it is (per the most detailed version found, agents-txt.com's v1.0): a plain-text file at the site root listing supported protocols, e.g. Protocols: x402, mpp, with directives for pointing agents at an A2A AgentCard, an MCP endpoint, or other machine-readable capability declarations [1]. A second, independently maintained proposal (kaylacar/agents-txt) describes a similar but not identical capability-declaration format and claims IANA filing (#72/#73, "under review") and an active IETF Internet-Draft [2]. A third effort, agentstxt.dev, is reported by a Mastercard developer-documentation page to have had its IETF draft expire on 2026-04-10, with that same source describing "a fragmented landscape with 11+ competing proposals ... no ratified standard" [3]. A fourth, academic proposal in the arXiv paper "Towards an Agent-First Web" defines yet another agents.txt grammar (INI-style [agent-class] blocks with allow/rate-limit/content-format fields) without referencing any of the other three [4].

It solves, in principle, the problem of an agent needing to discover a site's supported protocols in one request rather than probing each well-known path individually — a genuine gap, since A2A, MCP, x402, and other protocols each define their own discovery convention but nothing ties them together at a single site level.

It does not currently solve that problem in practice, because there is no single agents.txt to fetch: an agent cannot know, without trying multiple grammars, which of at least four incompatible conventions (if any) a given site implements. None of the identified efforts has IETF ratification, and the one with the most third-party visibility (agentstxt.dev) had its own draft lapse.

Current state, as of this verification (September 2026): earliest dated public artifact found is the kaylacar/agents-txt GitHub repository, created 2026-02-22 and last updated 2026-07-18 [2]; agents-txt.com presents a v1.0 spec text with no stated publication date [1]; the Mastercard reference page's fragmentation characterization is dated to 2026 without a specific day [3]. No implementation count, adopter list, or resolution among the competing proposals was found.

What is disputed: everything about precedence, authorship, and which (if any) proposal will consolidate the space. This record should be treated as thin pending a resolution or a dominant implementation emerging.

Discovery and probe

Fixed filename at the site root · /agents.txt (well-known root path per all identified proposals; one proposal also allows /.well-known/agents.txt)

GET {origin}/agents.txt
parse:     200 response with a text/plain body listing supported protocols (e.g. `Protocols: x402, mpp`) or per-agent directives, per whichever competing grammar the site chose to implement
on absent: No agents.txt at the site root under any of the competing conventions; given the fragmentation, absence is a weak signal either way

Live check run by the MCP probe: GET /agents.txt. Competing agents.txt grammars share only the path; a non-empty file is the signal.

{
 "path": "/agents.txt",
 "expect": {
  "text_match": "\\S"
 },
 "note": "Competing agents.txt grammars share only the path; a non-empty file is the signal."
}

History

Instances

Every instance with its source is listed on the instances page.

See also

References

  1. agents-txt.com publishes a v1.0 'agents.txt Standard' spec: a text file at the site root declaring supported protocols (e.g. x402, mpp), with explicit sections relating it to A2A's AgentCard discovery and to RFC 9727's API Catalog — https://agents-txt.com/spec (2026) VERIFIED
  2. A separate GitHub proposal, kaylacar/agents-txt, describes itself as an open standard proposal for AI-agent capability declaration via a well-known URI, with IANA numbers #72/#73 'filed, under review' and an IETF Internet-Draft on Datatracker; the repository was created 2026-02-22 and last updated 2026-07-18 — https://github.com/kaylacar/agents-txt (2026-07-18) VERIFIED
  3. A Mastercard merchant-developer reference page lists agents.txt (at agentstxt.dev, a third distinct effort) as an 'Emerging Standard (Draft)' whose IETF draft expired 2026-04-10, describing 'a fragmented landscape with 11+ competing proposals (agent-manifest.txt, agents-brief.txt, etc.)' and 'no ratified standard' (may require login: HTTP 401 on one check and 200 on another, 2026-09-06) — https://developer.mastercard.com/merchant-cloud/documentation/tutorials-and-guides/agentic-commerce-guide/24/ (2026) REPORTED
  4. An arXiv paper, 'Towards an Agent-First Web', independently proposes its own agents.txt grammar (INI-style allow/rate-limit/content-format blocks per agent class) served at /.well-known/agents.txt, distinct from the other three — https://arxiv.org/html/2606.19116v1 (2026) VERIFIED

Disputed: "agents.txt" names at least four non-converging, mutually incompatible proposals (agents-txt.com's v1.0, kaylacar/agents-txt's IETF-draft capability format, agentstxt.dev's expired-draft format, and an academic paper's own INI-style grammar), none of which has become a ratified or dominant standard.

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