How to Make Your API Agent-Ready: A Developer Checklist

To make your API agent-ready, give a compatible client a documented route from a task to a confirmed result. That means clear operations, usable authentication, enforced permissions, structured responses and recovery rules. Test the route with the clients you intend to support. MCP, machine payments and a public agent name can help particular workflows; none is a universal prerequisite.

Start with one job your API already does well. Suppose an inventory service lets a customer check stock, reserve an item and release the reservation. Can an agent complete that sequence using the published instructions, with access limited to the correct warehouse? Can it tell when the reservation expires?

Start there. A folder full of metadata will not resolve a reservation whose state nobody can check.

1. Define the first workflow you will support

Choose a task with a result you can check. Keep the first integration small enough that you can find the problem when it fails. For our inventory example, the task is to reserve one available test item, confirm the reservation and release it.

Write a short operation brief before building the tool adapter. This is an internal planning format, not a protocol schema:

• Inputs: item identifier, quantity and the warehouse the caller may access.
• Effect: a temporary reservation; no order or payment is created.
• Authority: which account can reserve stock, and any quantity or approval limits.
• Result: reservation identifier, state and expiry time.
• Recovery: how to check an existing reservation and handle an uncertain write.
• Cleanup: how to release the reservation, including what happens after expiry.

Use that brief to agree on what the integration must do. If the underlying API cannot support part of this workflow, fix that gap before asking an agent to improvise around it.

2. Publish a contract and a short route into the docs

For an HTTP API, publish an OpenAPI description that matches the deployed service. Include stable, unique operation IDs, required inputs, constrained values, response schemas, security requirements and examples. Explain units, pagination and side effects where they affect the task.

The OpenAPI specification currently lists version 3.2.1. Use a version supported by your validators, generators and target clients; there is little value in publishing a contract your customers’ tools cannot read. Validate examples against the contract and compare the contract with actual responses.

A name such as reserve_inventory tells a client more than update_data. Its description should explain what stock is reserved, for how long, and whether anything is charged. Naming the operation clearly does not enforce those limits. The server must do that.

Give the client one starting URL. From there, it should be able to find authentication instructions, the API description, a working example, errors and support. Keep the instructions readable without navigating a logged-in dashboard.

If your docs are extensive, llms.txt can provide a curated entry point. Version 2 of the proposal allows files at the root or under a path such as /docs/llms.txt, and recommends links to Markdown alternatives. It remains a publishing proposal, not an access-control mechanism or a promise of search visibility.

You can also publish a workflow guide. If you distribute an installable skill using the Agent Skills format, its directory needs a SKILL.md with the required metadata. Hosting a Markdown page on your website does not automatically install it in every assistant. Publish the exact URL and explain how your supported clients use it.

3. Make authentication work from beginning to end

Decide whether the client will use an existing account, a delegated grant or a supported registration flow. Explain how it obtains a credential, where that credential belongs, how to check access and how to withdraw it. A human confirmation step can be part of a working agent flow.

WorkOS's auth.md proposal gives services a root-level registration guide alongside structured OAuth discovery metadata. Its current flow separates registration from credential issuance: a service-signed identity assertion is exchanged for an access token. Implement the flow you advertise, including its claim and revocation behavior, rather than copying only the Markdown file.

Our own implementation makes that distinction worth spelling out. Our live authentication guide documents direct API-key provisioning, identity lookup and key revocation. It also states that the full assertion-exchange flow and credential-specific scope enforcement are not yet implemented. A scope inventory in discovery metadata is not evidence that each issued key has a restricted grant.

Use the Headless Domains auth.md article for the registration background. For your own API, verify both a permitted call and a request that should be refused. Keep credentials in the application's secret-handling components, out of public instructions and model-visible output.

4. Expose tools your clients can actually use

The application behind a tool call turns the model's selected operation and arguments into a real API request. Give it narrow operations with clear input and output schemas. Validate arguments before execution and check the returned business result before reporting success.

MCP is useful when your intended clients support it. It is not required simply because an API has write operations. A direct integration can work too.

The current MCP tools specification supports structured results and optional output schemas. It also distinguishes protocol errors from tool execution failures reported with isError. Implement the protocol version your clients support; do not assume an old server example matches the current contract.

For a reservation workflow, return the reservation identifier explicitly and require it on later calls. Avoid depending on an invisible conversational session to decide which reservation to release. Check the caller's access to that reservation every time.

For protected HTTP-based MCP servers, follow the MCP authorization requirements, including protected-resource discovery. The current guidance recommends Client ID Metadata Documents and retains Dynamic Client Registration as a deprecated compatibility option. Local STDIO integrations use a different credential-handling approach. Match your implementation to its actual transport and client support.

Keep retrieved content and tool output separate from the instructions that govern access. A product description should never be able to grant export permission. Tool descriptions and annotations do not enforce approval either. Put tenant, object and action checks in the service or an enforcement layer the agent cannot bypass. If approval is required, bind it to the actual requested action and its relevant arguments.

OWASP's object-level authorization guidance applies here: knowing an object's identifier does not give a caller permission to use it. Our enterprise access-control guide covers the deeper permission tests.

5. Define completion, errors and recovery

Tell callers what a completed operation looks like. An accepted job may still be running. A successful HTTP exchange may contain a business error. Return identifiers and state that let the client check the actual result.

For HTTP error bodies, RFC 9457 Problem Details provides a standard format. Document your problem types and any extension fields. Include useful context without exposing secrets or sensitive internal details.

Set limits on attempts, elapsed time and response size. Explain pagination and rate-limit behavior so the client can stop without guessing. Then define what it should do after validation failures, expired credentials and uncertain writes. A single retryable flag cannot capture every condition needed to repeat an operation safely. Preserve the original operation identifier and follow the receiver's documented deduplication or status-lookup contract. The agent retry and idempotency guide provides the decision card and failure experiments.

Make important calls traceable through the adapter to the receiving service. Retain the authenticated caller, relevant agent and run references, authorization decision and result identifier. Shared connector credentials need an additional maintained mapping if you want to identify the initiating agent. Use the API call attribution exercise to check that connection.

6. Explain costs before the first billable action

An existing subscription or account-billing arrangement may be enough. Publish billing units, limits, approval thresholds and what happens when the budget is exhausted. Free APIs can skip payment integration entirely.

If you need machine payments, x402 and MPP offer programmatic payment flows. Choose a supported implementation on both sides and document how callers reconcile payment with delivery. Payment approval, access permission and successful completion remain separate checks.

Keep your existing website and API host. These payment protocols do not require a special domain extension. Our agent payment protocol comparison handles that implementation choice in detail.

7. Run a release check with the intended clients

Use a test environment and synthetic data. Give a supported client the starting URL, the task and its allowed boundaries. Record its model, tools and integration versions, along with any manual intervention. Test credentials should come through the intended credential path, not a secret pasted into the prompt.

For the inventory workflow, keep evidence for these checks:

1. Discovery: the client finds the correct operation and understands the reservation's expiry and effects.
2. Access: it obtains the intended credential or completes the documented human handoff.
3. Execution: the test reservation exists with the expected item, quantity and state.
4. Boundary: a request for another tenant's stock is refused without disclosing or changing it.
5. Recovery: an interrupted attempt is resolved under the documented contract, or remains explicitly unresolved.
6. Cleanup: the reservation is released and withdrawn access stops working within the documented interval.

Tell integrators which client configurations you tested and where they still need help. Repeat the relevant checks when schemas, authentication, tools or service behavior change. A result from one client is evidence about that configuration, not every agent.

Our Docka signup evaluation illustrates that distinction. Its successful signup runs support a claim about onboarding; they do not establish that every later workflow works or that all security controls passed.

Give the public service a maintained identity

Once the workflow works, make its official information easy to find again. A Headless Domains name can provide a persistent public reference for an agent or agent-facing service, linking its operator, current interfaces and machine-readable records. Compatible clients can inspect those records through HTTPS APIs and command-line workflows.

You can keep the API on its current host. Maintain the public record when its endpoint, operator or instructions change, and give callers a support route when automation stops.

Use the documented Headless Domains manifest format and supported record controls. Do not assume arbitrary fields copied from a blog example are accepted API inputs. Published capabilities and proof references still need to be checked by the relying system.

Headless Domains also documents Action Cards for supported integrations. These describe published actions and their providers. The PowerLobster Service adapter currently provides read-only discovery, not a purchase action. Finding a card does not authorize execution or payment.

The Agent Identity Stack explains the broader architecture. Use this checklist when you are preparing the API itself for an agent to use.

Common implementation questions

Do I need to rebuild my API for agents?

Often you can keep the existing API and improve its documentation, contract and client adapter. Backend changes are needed where the workflow lacks required access checks, completion evidence or recovery behavior.

Does publishing OpenAPI automatically make my API callable by an assistant?

No. The assistant needs a compatible integration that exposes the operations, handles credentials and executes requests. Validate that integration with the actual client you plan to support.

Is a directory listing required?

No. A listing can help people discover a public service. It does not replace a working integration, prove safety or guarantee use by an AI assistant.

Put one working integration into use

Pick one task, publish the instructions and check that a client can finish it within the permitted boundaries. Fix the first point where it needs undocumented help.

When that service needs a public identity across tools and platforms, give your agent the Headless Domains getting-started instructions. Ask it to explain the registration options and prerequisites before creating an account or spending money, then connect the name to the service you have tested.