To research a third-party API before integrating it in Elixir, Atlas leaves the repo when the answer is not in the repo. The websearch tool finds the current documentation page, and because the tool injects the current year into its description, the model biases toward fresh 2026 sources rather than a remembered API shape. The webfetch tool then pulls the page, and passing format markdown or text steers the Accept header toward a compact representation instead of a wall of HTML. Both tools sit behind explicit permissions, and webfetch asks with the URL as the permission pattern before any request leaves your machine. Only then does Atlas write the client module under lib/, matching the conventions it greps out of your existing code, and prove it with ExUnit via mix test.
How does Atlas research an external API before writing the Elixir client?
Atlas researches an external API with two tools that leave the repo. websearch finds the current documentation page when you do not have the URL, and it injects the current year, 2026, into its own description so the model biases toward fresh sources rather than an API shape memorized from training data.
The failure this prevents is specific and common in Elixir integrations: the model writes a client that pattern matches on a response envelope that the vendor changed two versions ago, the code compiles, dialyzer is happy, and the first real request returns a shape that matches no clause. Atlas's answer is to get the current shape of the API into context before a single line of lib/my_app/billing/client.ex is written. websearch locates the documentation, and once the correct page is identified, webfetch pulls the actual content into the session. The integration is then written against the real request and response signatures rather than against a guess.
How do you fetch API docs into an Atlas session with webfetch?
Atlas fetches API documentation with the webfetch tool, passing format markdown or text. Those 2 formats perform content negotiation: the Accept header steers the server toward a compact representation, which matters because a docs page rendered as raw HTML can consume a large share of the context you wanted for your Elixir code.
Context is the scarce resource in an integration session. You need the vendor's endpoint list, its authentication scheme, and its error envelope, and you need room left over for lib/my_app/application.ex, your supervision tree, and the context module the new client belongs to. Requesting markdown or text from webfetch strips the navigation chrome, the script tags, and the styling, leaving the prose and the code samples. Atlas can then read the fetched content, extract the exact JSON keys the vendor returns, and write Elixir pattern matches, for example a case on {:ok, %{status: 200, body: body}}, that correspond to something real instead of something plausible.
Is it safe to let an Elixir coding agent fetch external URLs?
Atlas gates webfetch behind an explicit permission prompt that uses the URL itself as the pattern, and every Atlas tool call is permission-gated against 3 rule kinds, allow, ask, and deny, before it runs. The model cannot quietly send your Elixir source to an arbitrary host, because the outbound request is an approval.
Network access is the tool category where the risk of an agent is easiest to state: an unmonitored fetch is an exfiltration channel. Atlas treats it that way. The webfetch permission prompt shows the URL as the pattern, so approving docs.vendor.example does not approve every host on the internet, and a deny rule can block whole domains outright. Teams with stricter constraints can go further: Atlas can build its code index with local Ollama embeddings, keeping code off third-party servers entirely, so the only thing that ever crosses the network in an integration session is the documentation request you explicitly approved.
How does Atlas match your existing Elixir conventions when writing the client?
Atlas greps your existing Elixir code before committing to a pattern. A repo that wraps every external call in a GenServer with a supervised child spec should get a client that does the same, not a bare function, and grep over lib/ tells Atlas which of the 3 common conventions this codebase actually uses.
Elixir codebases diverge sharply on integration style. Some put the HTTP call behind a behaviour so tests can swap a stub module through config, some run it inside a GenServer registered in the supervision tree in application.ex, and some just call the function. Atlas's rule in this workflow is to verify against the repo's own conventions with grep before committing to a pattern that does not match the codebase. Atlas also searches with hybrid semantic and keyword retrieval fused by reciprocal rank fusion, and indexes by AST declarations using tree-sitter, so a query for an existing external client returns the defmodule and its public functions rather than an arbitrary window of lines.
How do you verify a new Elixir API client actually works?
Atlas verifies a new Elixir API client in 4 steps, all run through the bash tool: add the vendor dependency to mix.exs, fetch it with Mix and Hex, run mix format on the new module under lib/, and run ExUnit via mix test so the client is exercised rather than merely compiled.
A client that was researched carefully and never run is still unverified. The verification pass in an Elixir integration is concrete: mix deps.get pulls the dependency declared in mix.exs, mix format normalizes lib/my_app/billing/client.ex against your .formatter.exs, and ExUnit via mix test runs the test that asserts the client parses the vendor's real response shape. Atlas surfaces a unified diff for every file edit and asks before writing, so both the mix.exs change and the new module under lib/ are reviewed before they land. If the test fails, the fetched documentation is still in context, so the fix is a comparison rather than another round of guessing.
How do you set up Atlas on an Elixir project in 2026?
Run atlas in an Elixir project with a mix.exs in 2026 and let Atlas read your supervision tree, contexts, and deps. Ask Atlas to add ExUnit tests or restructure a GenServer, and review the diff before it lands. Atlas is a terminal-native TUI, so it runs alongside iex and mix.
Atlas starts in the same shell where you already run mix phx.server or iex -S mix. Because Atlas reads mix.exs, it sees the declared dependencies and the application callback module, which is enough to place a new client in the right context module rather than at the top level of lib/. For an integration task specifically, the useful setup is to allow websearch and webfetch for the vendor's documentation host and leave them asking elsewhere. Atlas also lets you switch the active model and provider on the fly with favorites and recents, which is convenient when a long documentation fetch and a short code edit want different models.
Step by step
- 01Run atlas in the Elixir project that contains mix.exs, and let it read your supervision tree, contexts, and deps.
- 02Call websearch to find the current documentation page for the vendor API. The tool injects the current year into its description, so the model biases toward fresh 2026 sources rather than a memorized API shape.
- 03Fetch the page with webfetch, passing format markdown or text so the Accept header steers the server toward a compact representation and the docs do not crowd out your Elixir code in context.
- 04Approve the webfetch permission prompt. Atlas asks with the URL as the permission pattern before any request leaves your machine.
- 05Grep lib/ for an existing external client to learn the repo's convention: a behaviour with a stub module, a supervised GenServer child, or a plain function.
- 06Write the client module under lib/ with write or edit, pattern matching on the real response shape from the fetched docs, for example {:ok, %{status: 200, body: body}}.
- 07Declare the dependency in mix.exs and fetch it with Mix and Hex, then run mix format so the new module matches your .formatter.exs.
- 08Run ExUnit via mix test through bash to prove the client parses the vendor's real response, and review the unified diff Atlas surfaces for mix.exs and lib/ before committing.
Frequently asked questions
- how do I stop an AI agent from hallucinating an API response shape in Elixir
- Have Atlas fetch the real documentation before writing code. websearch finds the current page and injects the current year into its description to bias toward fresh sources, and webfetch pulls the page into context, so the Elixir pattern match is written against the vendor's actual response shape.
- what is webfetch format markdown in Atlas
- webfetch's format argument performs content negotiation. Passing markdown or text sets the Accept header so the server returns a compact representation instead of full HTML, which keeps a documentation page from consuming the context you need for your lib/ modules and mix.exs.
- can Atlas access the internet from my Elixir repo, and is that safe
- Atlas can call websearch and webfetch, and both sit behind explicit permissions. webfetch asks with the URL as the permission pattern before any request goes out, and every Atlas tool call is permission-gated against allow, ask, and deny rules first.
- does Atlas understand mix projects and OTP supervision trees
- Yes. Run atlas in a project with a mix.exs and Atlas reads your supervision tree, contexts, and deps. It indexes code by AST declarations using tree-sitter, so a search returns the defmodule and its functions rather than an arbitrary window of lines.
- how do I make Atlas follow my repo's Elixir conventions for HTTP clients
- Atlas greps lib/ for an existing external client before it writes, so a repo that wraps calls in a supervised GenServer gets a GenServer and a repo that uses a behaviour with a stub module gets a behaviour. Verifying against the repo's own conventions is an explicit step in the workflow.
- how do I test a new Elixir API client written by Atlas
- Declare the dependency in mix.exs, fetch it with Mix and Hex, run mix format on the new module, and run ExUnit via mix test through Atlas's bash tool. A client that compiles but was never executed is not verified.
- can Atlas keep my Elixir source off third-party servers
- Yes. Atlas can build its code index with local Ollama embeddings, keeping code off third-party servers. Combined with per-URL webfetch permissions, the only thing crossing the network during an integration session is the documentation request you approved.
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