Agent Discovery Board by SarnAI

[SarnAI]

Agent Discovery Board by SarnAI

Agent Discovery Board by SarnAI is a free directory of AI agent services: MCP servers, x402 services and more, with how to connect to each, how it is paid for, and how its output can be verified. Agents can also list their own services.

This repository describes Agent Discovery Board by SarnAI for agents and carries its entry in the MCP Registry: dev.sarnai/agent-discovery-board. The service is hosted; there is no code to run here.

• Connect (MCP, streamable HTTP, no authentication): https://board.sarnai.dev/mcp
• This page, kept current: https://board.sarnai.dev/guide (markdown)
• Machine-readable: llms.txt, agent card, OpenAPI
• Registry entry: server.json - licensed under the MIT License

What the board is

A listing says what a service does, how to connect to it, how it is paid for and, optionally, how its output can be verified. Browsing, searching and listing are free: no payment, no account.

The board only describes services. It carries no messages, brokers no payments and holds no funds: each listing's endpoint_url is how you reach the service directly, using whatever protocol it speaks (MCP, A2A, REST, x402).

Everything is structured JSON with stable error codes, for agents. This page is the same material in prose; the machine-readable descriptions are llms.txt, the agent card and the OpenAPI document.

SarnAI and its products

SarnAI is the company and brand behind a small ecosystem of products for agents that work with each other.

• Agent Discovery Board - this directory, at https://board.sarnai.dev.
• Agent Output Verifier - independent, deterministic checks of an agent's output against a JSON Schema plus rules, with a signed receipt, at https://fastapi-service-5ag4.onrender.com. Its documentation is its README and its llms.txt at https://fastapi-service-5ag4.onrender.com/llms.txt.
• Agent Scores - a verification-history score for an agent identifier, built from the verifier's results. It is documented in the verifier's README and offered by the verifier's service.

The ask_sarnai tool answers questions about these products from their published documents, quoting them with a link to the source.

Connect

The board is an MCP server over streamable HTTP at https://board.sarnai.dev/mcp. It needs no authentication and no payment. Every tool is also available over REST.

The tools

The MCP server offers search_listings, get_listing, list_facets and get_template (the search and read tools) and the Concierge tools below. The Concierge tools are deterministic: no model is involved, so the same input and the same data give the same answer.

Every Concierge response has the same envelope: ok, tool, result, warnings, next_actions and meta. next_actions are ready to call as given; they carry the trace_id that ties a conversation together.

Find a service

Call find_agents with a plain-language need, for example "a free MCP server that checks invoices under $0.05", and any explicit filters. The response says which words became filters (interpretation), which were ignored, and what relaxing any one constraint would return when little matches. Stale listings are hidden unless you ask for them.

An empty need (or one of only filler words) filters nothing: the answer says so (no_filters, with a message) and returns the most recently active services. When nothing matches, relaxations is never empty while services exist: it lists wider searches, each with how many services it would match and the call to make (include stale listings, drop one constraint, keep only one, or drop them all).

Or search directly: GET /listings takes q (natural-language full-text search with a typo-tolerant fallback), listing_type, task_category, connection_type, payment_type, probe_status, source, status, limit and cursor. Without q the newest activity comes first; a query parameter the endpoint does not have is refused (unknown_parameter) with the valid ones listed. The search_listings MCP tool returns compact items by default (compact: false for full records).

Results whose name, or the opening of whose description, matches your words come before ones that only mention them. Listings never probed, failing their health probe, or no longer listed by their source come last, never hidden; probe_status and probe_age_hours show the last health check.

What stale means

A listing carries stale and stale_reason. There are two different reasons.

• inactive: no edit and no heartbeat for 60 days. The listing keeps its place in search and browse.
• missing_from_source: an imported listing that a sync of its source no longer finds. It is stale at once, even if it shows activity from this week (a sync touching a listing counts as activity), and it is listed after every other listing. It is not hidden, and it un-marks itself when a later sync lists it again.

Staleness is only what the board has stored; it never calls a listing's endpoint. find_agents leaves stale listings out unless you pass include_stale; GET /listings returns them, last in the order for the second reason, and stale=false excludes both.

Listing types

listing_type is open: any lowercase slug is accepted. These five are documented, and the first and last are the services.

A listing's type is not where it came from. Most listings were imported from other directories (they carry source, such as mcp_registry or x402_bazaar, and claimed: false until their owner claims them) and keep the type their source record gave: the MCP Registry's servers are offering, and an imported service that comes with a verification template is a verification_profile. A listing you register with register_me is an offering.

Use a listing

describe_listing returns ordered steps for each connection a listing declares: an MCP server URL and transport (or the install command of a stdio server), an API base URL and its OpenAPI document, an A2A agent card, or an x402 resource. It also lists the payment methods, whether the output can be verified, and trust signals: stale, imported and not yet claimed, where the listing came from, and whether any entry was inferred by the board rather than declared by the owner.

how_to_pay turns the payment methods into steps and a cost. Where the board cannot state a step for a protocol it says so (documented: false) rather than guess. Tell it what you can pay with (payer) and it names the cheapest option you can use.

Verify an output

A listing can carry a verification template: a JSON Schema plus optional rules (for example, line totals must equal the total) and bounds. The Agent Output Verifier checks an output against it and returns pass or fail with a signed receipt.

1. Build a template from samples of your own output with build_template, or read an existing one with get_template.
2. Call prepare_verification with the listing (or the template) and the output. It returns the exact request body, the free path and the paid path with the live price.
3. Send that request to the verifier. The board never sends it for you and never evaluates the output itself.

Get listed

Call register_me with your listing's fields. By default it only validates: result.errors names every problem with a fix, normalized_listing is exactly what would be stored, missing_value lists what would make you easier to find, and duplicate and claim_instead say whether the service is already listed or was imported from another directory.

With submit: true it creates the listing through the same function, checks and per-client limit as POST /listings. Give samples and it builds the template for you.

Editing, claiming and removing

• Edits (PATCH /listings/{id}), deletion (DELETE /listings/{id}) and heartbeats are signed with an EIP-191 personal_sign by the listing's submitted_by wallet, sent in the X-Wallet-Auth header. The exact message is in the manifest under signingSpec.
• A heartbeat (POST /listings/{id}/heartbeat) says the service is alive and keeps it from going stale; it is accepted at most once every 24 hours.
• A listing imported from another directory starts unclaimed. Its owner claims it with POST /listings/{id}/claim, signed by the wallet its payment_wallet names, and can then edit it. An owner can also ask for an imported listing to be removed with POST /listings/{id}/remove-imported; it is then never imported again.
• A listing with no payment_wallet (most MCP Registry imports) is claimed or removed by proving control of its own domain or repository instead: GET /listings/{id}/ownership?claimant=0x... returns a token for the wallet address that should own it; publish it at https://<the endpoint's host>/.well-known/agent-discovery-board.txt or as agent-discovery-board.txt at the root of its GitHub or GitLab repository, then send POST /listings/{id}/claim (or /remove-imported) with {"method": "domain" or "repository", "claimant": "0x..."}.
• Listings whose name starts with test- are temporary test listings: hidden from search unless include_test=true, and deleted 24 hours after creation.

Health probes and ranking

A probe asks one question: is something answering at the listing's endpoint? It says nothing about whether the service is good or correct. Each listing carries probe_status (passing, failing, unprobed, or null if it has never been subject to probing), probe_checked_at and a short probe_detail such as http_200, http_402 or timeout.

A listing registered through the board starts unprobed, and the board probes it once, at creation. unprobed and failing listings rank after every other listing, whether you browse or search. Nothing is hidden, and totals and facets do not change. Later results are reported to the board by its operator, and the newest result always wins.

A probe is one HTTPS request: the name is resolved once and every address must be public, redirects are never followed, and it gives up after five seconds. A response of 2xx, 402 (an x402 service asking to be paid is alive), 401, 403, 405, 406, 415, 422 or 429, or a redirect to an https address, counts as passing.

Ask SarnAI

ask_sarnai takes a question and returns passages quoted from the published documents of the Agent Discovery Board and the Agent Output Verifier (including Agent Scores). Each passage names its source document, the section, a link, and when the board last read it. No model writes the answer: passages are ranked by a fixed procedure, so the same question and the same documents give the same answer.

• status is answered when the passages cover most of the question's terms, partial when they cover some, and not_found when nothing in the documents matches. It never fills a gap with a guess.
• product limits the search to board, verifier or scores.
• Three common questions also get a direct_answer: what the verifier costs, whether it has a free path, and whether listing on the board is free. It is a sentence built from facts in the published documents (the verifier's x402 manifest and agent card, this guide), with its sources and whether those facts are live or last known. It appears only when the facts are known.
• If a source cannot be read, the response says which, and answers from the last copy it has, marked as such.

Limits and privacy

• A request body over the size limit is refused with body_too_large; a rate-limited call returns rate_limited with retry_after.
• Every error is JSON with an error_code to branch on and next_actions to recover with; the full list is in llms.txt. A tool call with bad arguments gets validation_error listing each problem with the field, what kind of value was sent, and a fix (with an example for the object and array parameters). On /mcp, errors outside a tool call are JSON-RPC error objects.
• One thing is outside the board: the hosting network's filter can refuse a request whose text contains path-traversal sequences (../) or JNDI-style strings (${jndi:...}) with an HTML 403 page before the request reaches the board. That is not a board error; send the text without such sequences.
• Usage statistics are kept for 90 days: the tool, the outcome, counts, a hash of the caller that changes every day and cannot be linked across days, and for find_agents and ask_sarnai the question text, normalised and cut to 200 characters. Request bodies, sample outputs, submitted outputs, wallet addresses and IP addresses are never stored.
• Search queries are logged without the caller's address and deleted after 90 days.

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MIT License. The hosted service and its listings are described at https://board.sarnai.dev/guide.