deepseek-harness/packages/web/web/README.md

description, kind

description	kind
The web access service (ctx.web): how deployments and plugin authors search the web and fetch URLs through interchangeable providers, with one selection policy and error vocabulary.	package-reference

@deepseek-ai/dsh-web

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Summary

Any plugin or tool can search the web or fetch a URL through dsh-web (ctx.web) without binding to any vendor's API. Search and fetch providers plug in as backends, and the service picks one usable provider per operation, so callers never track which vendor runs behind a call. Choose it when building web tooling or another backend; the shipped model-facing tools (dsh-tool-web) mount it automatically. The service itself makes no network calls and registers no model-facing tool: a provider must be mounted before search or fetch can run. Search and fetch share one selection policy, one cancellation and error vocabulary, and one configuration surface, so "how this harness reaches the web" has a single owner.

Table of Contents

• Use this package
• Understand the implementation
• Further Exploration
• Model Experience
• Known Limitations and Deferred Work
• Dev Note

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Use this package

A composition that needs web access loads the dsh-web service and mounts at least one backend — a search provider and/or a fetch provider — and plugin or tool authors then call ctx.web.search() and ctx.web.fetch() directly. The service resolves the backend for each call, so callers never see provider ids unless they configured one.

When to choose it

Choose the service when a plugin or tool must search or fetch without hard-coding a vendor; a deployment that only uses the shipped web_search/web_fetch tools gets it for free through dsh-tool-web. You do not need it when the composition never reaches the web. The service adds no network access of its own: without at least one usable provider, every call fails with a structured WebError.

Minimal configuration

Load the service and let a single mounted backend auto-select, or pin a provider id with searchProvider/fetchProvider. The environment variables $DSH_WEB_SEARCH_PROVIDER and $DSH_WEB_FETCH_PROVIDER feed the same fields and are not a separate priority chain.

- name: '@deepseek-ai/dsh-web'
- name: '@deepseek-ai/dsh-web-search-exa'
- name: '@deepseek-ai/dsh-web-fetch-http'

Field	Default	Meaning
searchProvider	(unset)	Pinned search provider id; unset auto-selects when exactly one is usable
fetchProvider	(unset)	Pinned fetch provider id; unset auto-selects when exactly one is usable

The generated configuration catalog is the exhaustive source for every accepted field and its JSDoc.

Searching and fetching

search() runs one query and returns an optional provider answer plus a list of citeable sources; the service enforces request.maxResults by truncating sources[] and setting truncated. fetch() retrieves one URL and returns its final URL, status code, decoded body, and a truncation flag; a non-2xx response is a result, not an error.

// Search the web; sources[] is capped to maxResults:
const result = await ctx.web.search({ query: 'deepseek harness', maxResults: 8 })

// Fetch one URL; a non-2xx response is a result, not an error:
const page = await ctx.web.fetch({ url: 'https://example.com' })

Both calls accept an optional AbortSignal that is forwarded to the provider for cancellation. The normalized request and result shapes are the contract callers build on; the vocabulary section of the web subsystem reference describes them exhaustively.

Provider selection

Each call resolves its provider at execution time, and registration or load order never matters. A configured provider id wins when it is registered and usable; without a configured id, the service runs the single usable provider or fails clearly:

Situation	Outcome
configured id registered and usable	runs that provider
configured id not registered	WEB_PROVIDER_CONFIGURED_MISSING
configured id registered but unavailable	WEB_PROVIDER_CONFIGURED_UNAVAILABLE
no id, exactly one registered usable provider	runs it
no id, no usable provider	WEB_PROVIDER_UNAVAILABLE
no id, multiple usable providers	WEB_PROVIDER_AMBIGUOUS

A provider's availability is a cheap local check — for example whether its API key is present — and never makes network calls, so selection stays fast and deterministic.

Failures and recovery

Failures throw WebError with a stable, machine-routable code; the message adds detail such as the missing provider id or the ambiguous candidate set. Callers route on the code and decide how to degrade. To change which backend a call uses, reconfigure the pinned id, mount or unmount providers, or fix the provider's configuration so its availability check passes.

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Understand the implementation

Implementation internals — click to expand

This section explains the design decisions behind the service; the observable behavior is fully covered in Use this package.

Design philosophy

The package is built on one deliberate separation:

• One seam, two independent operations. Search and fetch share no request schema and no business logic, but they share one service so provider selection, cancellation, errors, and product configuration have a single owner. The parallel Search/Fetch method pairs are intentional.
• Selection is never order-dependent. A capability either pins a provider id or auto-selects when exactly one usable provider is registered; search()/fetch() resolve the provider at execution time.
• The service owns the result bound. maxResults is enforced by the seam after the provider returns, so an over-returning provider can never leak more sources than the caller asked for.

Source map

File	Role
src/index.ts	Plugin entry: the WebRuntime service, both provider registries, and execution-time selection
src/types.ts	Vocabulary: request/result types, the closed WebFetchBody union, and the WebError taxonomy
src/invariant.ts	Invariant companion (no runtime invariant; contracts are enforced at the service)

Data model

The request and result types define the normalized vocabulary callers build on — one Search pair and one Fetch pair — and the exhaustive fields and JSDoc live in src/types.ts and the web subsystem reference. Two deliberate choices shape them: WebFetchBody is a closed union (html | text) owned here, so adding a kind breaks compilation until every consumer handles it; WebError extends HarnessError with an open-string code, so consumers must tolerate provider-specific values. Source fields stay optional because not every provider returns all of them.

Selection flow

At call time the service resolves the provider — configured id first, then the unique usable provider — and throws the matching WebError when no clear winner exists. A search result then passes through capSources, which truncates sources[] to maxResults and flags truncated. Registration is effect-based: providers register with the calling fiber and unregister when it disposes, and a duplicate id within a capability kind is rejected at registration.

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Further Exploration

Read these pages when the package-level contract is not enough. They move from the shared vocabulary to the shipped backends, the model-facing tools, and the design rationale.

• Web subsystem — the exhaustive search/fetch requests and results, provider availability, and error codes.
• Web package map — the six-package family and each role.
• dsh-tool-web — the model-facing web_search and web_fetch tools over this service.
• dsh-web-fetch-http — the shipped anonymous HTTP(S) fetch backend.
• Generated configuration catalog — every accepted config field and its source declaration.
• Web capability seam decision — why search and fetch share one provider-selection service.

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Model Experience

Indirectly, through dsh-tool-web, which renders the seam's normalized search results and fetch bodies to the model while this service contributes no prompt or schema.

KV Cache effect

No direct invalidation; the named consumer owns any request-prefix changes.

Known Limitations and Deferred Work

These limits define when the service is incomplete on its own. They are current package constraints.

• No observation surface — there is no provider-change event and no capability-status query; availability is observable only by running a search or fetch and routing the thrown code, and the no-provider failure is the generic WEB_PROVIDER_UNAVAILABLE with no per-provider reason enumeration (Agent Note).
• Search requests carry only query and maxResults — provider-neutral controls (recency, domain filters, regional hints, search depth) are deferred until the backends can honor them (seam Agent Note).
• WebFetchBody has no pdf arm — text-extractable PDF support is named deferred work; the closed union makes adding it a compile-enforced change across the web packages.
• Provider-backed page extraction is out of scope of fetch() — a Firecrawl/Tavily-style web_extract capability is deferred rather than widening the fetch operation.

Dev Note

Working context for maintainers — click to expand

This Dev Note is working context for maintainers: open questions and undecided directions. It is explicitly non-authoritative — shipped behavior, limits, and rationale live in the sections above and the linked Agent Notes.

Future: observing provider state

No provider-change event or capability-status query exists; consumers observe availability only by executing a call and routing the thrown code. Restoring a small observation surface is possible if a consumer needs per-provider reasons, but the archived simplification note records why the earlier one was dropped.